Which fish species is it?

Which fish species is it?

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Today we found this kind of fish on the shore of Baltic Sea near Gdansk (PL). It is a very thin "fish" with some kind of a needle in place of nose. It was about 5 cm long and very lively. What is the name of the species?

PS. Kids caught it into a bucket just to take a pic - we released the creature just after the photo session :)

This looks like a pipefish, possibly a straightnose pipefish.

See also. But the size suggests a juvenile?

Biology and Physiology of Freshwater Neotropical Fish

Biology and Physiology of Freshwater Neotropical Fish is the all-inclusive guide to fish species prevalent in the neotropical realm. It provides the most updated systematics, classification, anatomical, behavioral, genetic, and functioning systems information on freshwater neotropical fish species. This book begins by analyzing the differences in phylogeny, anatomy, and behaviour of neotropical fish. Systems such as cardiovascular, respiratory, renal, digestive, reproductive, muscular, and endocrine are described in detail. This book also looks at the effects of stress on fish immune systems, and how color and pigmentation play into physiology and species differentiation.

Biology and Physiology of Freshwater Neotropical Fish is a must-have for fish biologists and zoologists. Students in zoology, ichthyology, and fish farming will also find this book useful for its coverage of some of the world’s rarest and least-known fish species.

Biology and Physiology of Freshwater Neotropical Fish is the all-inclusive guide to fish species prevalent in the neotropical realm. It provides the most updated systematics, classification, anatomical, behavioral, genetic, and functioning systems information on freshwater neotropical fish species. This book begins by analyzing the differences in phylogeny, anatomy, and behaviour of neotropical fish. Systems such as cardiovascular, respiratory, renal, digestive, reproductive, muscular, and endocrine are described in detail. This book also looks at the effects of stress on fish immune systems, and how color and pigmentation play into physiology and species differentiation.

Biology and Physiology of Freshwater Neotropical Fish is a must-have for fish biologists and zoologists. Students in zoology, ichthyology, and fish farming will also find this book useful for its coverage of some of the world’s rarest and least-known fish species.


In biology, a probe is a single strand of DNA or RNA that is complementary to a nucleotide sequence of interest.

RNA probes can be designed for any gene or any sequence within a gene for visualization of mRNA, [3] [4] [5] lncRNA [6] [7] [8] and miRNA in tissues and cells. FISH is used by examining the cellular reproduction cycle, specifically interphase of the nuclei for any chromosomal abnormalities. [9] FISH allows the analysis of a large series of archival cases much easier to identify the pinpointed chromosome by creating a probe with an artificial chromosomal foundation that will attract similar chromosomes. [9] The hybridization signals for each probe when a nucleic abnormality is detected. [9] Each probe for the detection of mRNA and lncRNA is composed of

20-50 oligonucleotide pairs, each pair covering a space of 40–50 bp. The specifics depend on the specific FISH technique used. For miRNA detection, the probes use proprietary chemistry for specific detection of miRNA and cover the entire miRNA sequence.

Probes are often derived from fragments of DNA that were isolated, purified, and amplified for use in the Human Genome Project. The size of the human genome is so large, compared to the length that could be sequenced directly, that it was necessary to divide the genome into fragments. (In the eventual analysis, these fragments were put into order by digesting a copy of each fragment into still smaller fragments using sequence-specific endonucleases, measuring the size of each small fragment using size-exclusion chromatography, and using that information to determine where the large fragments overlapped one another.) To preserve the fragments with their individual DNA sequences, the fragments were added into a system of continually replicating bacteria populations. Clonal populations of bacteria, each population maintaining a single artificial chromosome, are stored in various laboratories around the world. The artificial chromosomes (BAC) can be grown, extracted, and labeled, in any lab containing a library. Genomic libraries are often named after the institution in which they were developed. An example being the RPCI-11 library, which is named after Roswell Park Comprehensive Cancer Center (formerly known as Roswell Park Cancer Institute) in Buffalo, New York. These fragments are on the order of 100 thousand base-pairs, and are the basis for most FISH probes.

Preparation and hybridization process – RNA Edit

Cells, circulating tumor cells (CTCs), or formalin-fixed paraffin-embedded (FFPE) or frozen tissue sections are fixed, then permeabilized to allow target accessibility. FISH has also been successfully done on unfixed cells. [10] A target-specific probe, composed of 20 oligonucleotide pairs, hybridizes to the target RNA(s). Separate but compatible signal amplification systems enable the multiplex assay (up to two targets per assay). Signal amplification is achieved via series of sequential hybridization steps. At the end of the assay the tissue samples are visualized under a fluorescence microscope.

Preparation and hybridization process – DNA Edit

First, a probe is constructed. The probe must be large enough to hybridize specifically with its target but not so large as to impede the hybridization process. The probe is tagged directly with fluorophores, with targets for antibodies or with biotin. Tagging can be done in various ways, such as nick translation, or Polymerase chain reaction using tagged nucleotides.

Then, an interphase or metaphase chromosome preparation is produced. The chromosomes are firmly attached to a substrate, usually glass. Repetitive DNA sequences must be blocked by adding short fragments of DNA to the sample. The probe is then applied to the chromosome DNA and incubated for approximately 12 hours while hybridizing. Several wash steps remove all unhybridized or partially hybridized probes. The results are then visualized and quantified using a microscope that is capable of exciting the dye and recording images.

If the fluorescent signal is weak, amplification of the signal may be necessary in order to exceed the detection threshold of the microscope. Fluorescent signal strength depends on many factors such as probe labeling efficiency, the type of probe, and the type of dye. Fluorescently tagged antibodies or streptavidin are bound to the dye molecule. These secondary components are selected so that they have a strong signal.

FISH is a very general technique. The differences between the various FISH techniques are usually due to variations in the sequence and labeling of the probes and how they are used in combination. Probes are divided into two generic categories: cellular and acellular. In fluorescent "in situ" hybridization refers to the cellular placement of the probe

Probe size is important because longer probes hybridize less specifically than shorter probes, so that short strands of DNA or RNA (often 10–25 nucleotides) which are complementary to a given target sequence are often used to locate a target. The overlap defines the resolution of detectable features. For example, if the goal of an experiment is to detect the breakpoint of a translocation, then the overlap of the probes — the degree to which one DNA sequence is contained in the adjacent probes — defines the minimum window in which the breakpoint may be detected.

The mixture of probe sequences determines the type of feature the probe can detect. Probes that hybridize along an entire chromosome are used to count the number of a certain chromosome, show translocations, or identify extra-chromosomal fragments of chromatin. This is often called "whole-chromosome painting." If every possible probe is used, every chromosome, (the whole genome) would be marked fluorescently, which would not be particularly useful for determining features of individual sequences. However, it is possible to create a mixture of smaller probes that are specific to a particular region (locus) of DNA these mixtures are used to detect deletion mutations. When combined with a specific color, a locus-specific probe mixture is used to detect very specific translocations. Special locus-specific probe mixtures are often used to count chromosomes, by binding to the centromeric regions of chromosomes, which are distinctive enough to identify each chromosome (with the exception of Chromosome 13, 14, 21, 22.)

A variety of other techniques uses mixtures of differently colored probes. A range of colors in mixtures of fluorescent dyes can be detected, so each human chromosome can be identified by a characteristic color using whole-chromosome probe mixtures and a variety of ratios of colors. Although there are more chromosomes than easily distinguishable fluorescent dye colors, ratios of probe mixtures can be used to create secondary colors. Similar to comparative genomic hybridization, the probe mixture for the secondary colors is created by mixing the correct ratio of two sets of differently colored probes for the same chromosome. This technique is sometimes called M-FISH.

The same physics that make a variety of colors possible for M-FISH can be used for the detection of translocations. That is, colors that are adjacent appear to overlap a secondary color is observed. Some assays are designed so that the secondary color will be present or absent in cases of interest. An example is the detection of BCR/ABL translocations, where the secondary color indicates disease. This variation is often called double-fusion FISH or D-FISH. In the opposite situation—where the absence of the secondary color is pathological—is illustrated by an assay used to investigate translocations where only one of the breakpoints is known or constant. Locus-specific probes are made for one side of the breakpoint and the other intact chromosome. In normal cells, the secondary color is observed, but only the primary colors are observed when the translocation occurs. This technique is sometimes called "break-apart FISH".

Single-molecule RNA FISH Edit

Single-molecule RNA FISH, also known as Stellaris® RNA FISH, [11] is a method of detecting and quantifying mRNA and other long RNA molecules in a thin layer of tissue sample. Targets can be reliably imaged through the application of multiple short singly labeled oligonucleotide probes. [12] The binding of up to 48 fluorescent labeled oligos to a single molecule of mRNA provides sufficient fluorescence to accurately detect and localize each target mRNA in a wide-field fluorescent microscopy image. Probes not binding to the intended sequence do not achieve sufficient localized fluorescence to be distinguished from background. [13]

Single-molecule RNA FISH assays can be performed in simplex or multiplex, and can be used as a follow-up experiment to quantitative PCR, or imaged simultaneously with a fluorescent antibody assay. The technology has potential applications in cancer diagnosis, [14] neuroscience, gene expression analysis, [15] and companion diagnostics.

Fiber FISH Edit

In an alternative technique to interphase or metaphase preparations, fiber FISH, interphase chromosomes are attached to a slide in such a way that they are stretched out in a straight line, rather than being tightly coiled, as in conventional FISH, or adopting a chromosome territory conformation, as in interphase FISH. This is accomplished by applying mechanical shear along the length of the slide, either to cells that have been fixed to the slide and then lysed, or to a solution of purified DNA. A technique known as chromosome combing is increasingly used for this purpose. The extended conformation of the chromosomes allows dramatically higher resolution – even down to a few kilobases. The preparation of fiber FISH samples, although conceptually simple, is a rather skilled art, and only specialized laboratories use the technique routinely. [16]


Q-FISH combines FISH with PNAs and computer software to quantify fluorescence intensity. This technique is used routinely in telomere length research.

Flow-FISH Edit

Flow-FISH uses flow cytometry to perform FISH automatically using per-cell fluorescence measurements.


Microfluidics-assisted FISH (MA-FISH) uses a microfluidic flow to increase DNA hybridization efficiency, decreasing expensive FISH probe consumption and reduce the hybridization time. MA-FISH is applied for detecting the HER2 gene in breast cancer tissues. [17]


Microautoradiography FISH is a technique to combine radio-labeled substrates with conventional FISH to detect phylogenetic groups and metabolic activities simultaneously. [18]

Hybrid Fusion-FISH Edit

Hybrid Fusion FISH (HF-FISH) uses primary additive excitation/emission combination of fluorophores to generate additional spectra through a labeling process known as dynamic optical transmission (DOT). Three primary fluorophores are able to generate a total of 7 readily detectable emission spectra as a result of combinatorial labeling using DOT. Hybrid Fusion FISH enables highly multiplexed FISH applications that are targeted within clinical oncology panels. The technology offers faster scoring with efficient probesets that can be readily detected with traditional fluorescent microscopes.

Often parents of children with a developmental disability want to know more about their child's conditions before choosing to have another child. These concerns can be addressed by analysis of the parents' and child's DNA. In cases where the child's developmental disability is not understood, the cause of it can potentially be determined using FISH and cytogenetic techniques. Examples of diseases that are diagnosed using FISH include Prader-Willi syndrome, Angelman syndrome, 22q13 deletion syndrome, chronic myelogenous leukemia, acute lymphoblastic leukemia, Cri-du-chat, Velocardiofacial syndrome, and Down syndrome. FISH on sperm cells is indicated for men with an abnormal somatic or meiotic karyotype as well as those with oligozoospermia, since approximately 50% of oligozoospermic men have an increased rate of sperm chromosome abnormalities. [19] The analysis of chromosomes 21, X, and Y is enough to identify oligozoospermic individuals at risk. [19]

In medicine, FISH can be used to form a diagnosis, to evaluate prognosis, or to evaluate remission of a disease, such as cancer. Treatment can then be specifically tailored. A traditional exam involving metaphase chromosome analysis is often unable to identify features that distinguish one disease from another, due to subtle chromosomal features FISH can elucidate these differences. FISH can also be used to detect diseased cells more easily than standard Cytogenetic methods, which require dividing cells and requires labor and time-intensive manual preparation and analysis of the slides by a technologist. FISH, on the other hand, does not require living cells and can be quantified automatically, a computer counts the fluorescent dots present. However, a trained technologist is required to distinguish subtle differences in banding patterns on bent and twisted metaphase chromosomes. FISH can be incorporated into Lab-on-a-chip microfluidic device. This technology is still in a developmental stage but, like other lab on a chip methods, it may lead to more portable diagnostic techniques. [20] [21]

Species identification Edit

FISH has been extensively studied as a diagnostic technique for the identification of pathogens in the field of medical microbiology. [22] Although it has been proven to be a useful and applicable technique, it is still not widely applied in diagnostic laboratories. The short time to diagnosis (less than 2 hours) has been a major advantage compared with biochemical differentiation, but this advantage is challenged by MALDI-TOF-MS which allows the identification of a wider range of pathogens compared with biochemical differentiation techniques. Using FISH for diagnostic purposes has found its purpose when immediate species identification is needed, specifically for the investigation of blood cultures for which FISH is a cheap and easy technique for preliminary rapid diagnosis. [22]

FISH can also be used to compare the genomes of two biological species, to deduce evolutionary relationships. A similar hybridization technique is called a zoo blot. Bacterial FISH probes are often primers for the 16s rRNA region.

FISH is widely used in the field of microbial ecology, to identify microorganisms. Biofilms, for example, are composed of complex (often) multi-species bacterial organizations. Preparing DNA probes for one species and performing FISH with this probe allows one to visualize the distribution of this specific species within the biofilm. Preparing probes (in two different colors) for two species allows researchers to visualize/study co-localization of these two species in the biofilm and can be useful in determining the fine architecture of the biofilm.

Comparative genomic hybridization Edit

Comparative genomic hybridization can be described as a method that uses FISH in a parallel manner with the comparison of the hybridization strength to recall any major disruptions in the duplication process of the DNA sequences in the genome of the nucleus. [23]

Virtual karyotype Edit

Virtual karyotyping is another cost-effective, clinically available alternative to FISH panels using thousands to millions of probes on a single array to detect copy number changes, genome-wide, at unprecedented resolution. Currently, this type of analysis will only detect gains and losses of chromosomal material and will not detect balanced rearrangements, such as translocations and inversions which are hallmark aberrations seen in many types of leukemia and lymphoma.

Spectral karyotype Edit

Spectral karyotyping is an image of colored chromosomes. Spectral karyotyping involves FISH using multiple forms of many types of probes with the result to see each chromosome labeled through its metaphase stage. This type of karyotyping is used specifically when seeking out chromosome arrangements.

Poecilia latipinna

Sailfin Molly. Image © Noel Burkhead

These small, oblong fish are generally gray with rows of spots that almost blend to look like stripes. Males have an enlarged dorsal fin, but otherwise they have small fins in general, including a truncated caudal (tail) fin. Their upturned faces help them draw from the upper layer of oxygen-rich water, allowing them to thrive in poor quality water. They can be found in ponds, marshes, and even roadside ditches, and they are popular with aquarists, who have bred a wide variety of colors with this tolerant fish.

Order – Cyprinodontiformes Family – Poeciliidae Genus – Poecilia Species – latipinna

Common Names

Sailfin molly, Breitflossenkärpfling (German), bubuntis (Tagalog), Molinezja szerokopletwa (Polish), molliénésie á voilure (French), and tabai (Hawaiian).

Importance to Humans

Freshwater marshes provide habitat for sailfin mollies. Image © Florida Museum of Natural History

The sailfin molly, in its many color varieties is of considerable interest and value to aquarists and many artificially selected varieties are produced and sold in pet shops. Naturally occurring populations of sailfin mollies may help to control mosquito populations by feeding on the larvae and pupae of these pests.


This species is not listed as threatened or vulnerable by the World Conservation Union (IUCN). The IUCN is a global union of states, governmental agencies, and non-governmental organizations in a partnership that assesses the conservation status of species.

Geographical Distribution

World distribution map for the sailfin molly

The sailfin molly is found in fresh, brackish, and coastal salt water in coastal lowland habitats from North Carolina to Texas and the Yucatan Peninsula of Mexico. Prefering marshes, lowland streams, swamps, and estuaries, the sailfin molly is very common in peninsular Florida. Non-indigenous populations are established in the western U.S. and in Hawaii. Sailfin mollies introduced to California have caused a decline in populations of the federally endangered desert pupfish (Cyprinodon macularius).


Sailfin mollies are most commonly observed in the shallow surface waters along the edges of marshes, lowland streams, ponds, swamps, estuaries and even ephemeral water bodies such as roadside ditches. Small to large aggregations of the species are most commonly found under floating vegetation or near structures in the water, minimizing their chances of being observed by potential predators.

The sailfin molly is a tolerant species. By exploiting the thin film of oxygen rich surface water with their upturned mouths, sailfin mollies are able to survive oxygen depleted habitats. A euryhaline species, the sailfin molly may be found in a variety of saline environments and will breed in brackish waters.


Male (right) and female (left) sailfin molly. Images © George Burgess

Distinctive Features
The body of the sailfin molly is essentially oblong. The head is small and dorsally flattened, with a small, upturned mouth. The caudal peduncle is broad and the caudal fin is large, rounded, and sometimes tipped with black. The pelvic fins originate at a point anterior to the dorsal fin. The dorsal fin is greatly enlarged in mature males and somewhat enlarged in females. It is this conspicuous and attractive feature that lends the species its prevailing common name.

Sailfin molly. Image courtesy U.S. Geological Survey

The body is generally light gray, although breeding males may be greenish-blue. Several rows of spots occur along the sides, back, and dorsal fin. Often times these spots blend together or are very close to one another, creating an appearance of stripes. Aquarists have developed many color variations in this species, and indeed much variation occurs naturally in the wild, with melanistic and speckled forms known.

Sailfin mollies possess many rows of very small teeth, the outer row of which are the largest.

Size, Age, and Growth
The natural lifespan of sailfin mollies, like other small poeciliids, is short, particularly in the case of the males, which may live less than one year after achieving sexual maturity. Depending upon environmental conditions sailfin mollies may become reproductively in less than a year. Sailfin mollies are small fish. At one year of age males typically range in size from 15-51 mm SL while mature females are likely to be approximately 19-53 mm SL. The sizes of adult males is directly correlated with population density. The greater the population, the smaller the average size of males. The maximum recorded size for this species is 150 mm TL.

Sailfin mollies feed on aquatic insects including mosquito larvae. Image courtesy Center for Disease Control

Food Habits
Sailfin mollies feed primarily upon algae and other plant materials, although they will consume a number of aquatic invertebrates including the larvae of mosquitos.

Female sailfin mollies tend to be larger than males, a disparity typical of the Poeciliidae. Males exhibit large and colorful dorsal fins in addition to a colorful caudal fin and these conspicuous secondary sexual features play a role in female mate choice. Fertilization is internal and is accomplished by means of highly modified fin elements within the anal fin of males that form a structure known as the gonopodium. Sailfin mollies produce broods of 10-140 live young, depending upon maturity and size, and females may store sperm long after the demise of their relatively short-lived mates. The gestation period for this species is approximately 3-4 weeks, depending upon temperature, and a single female may give birth on multiple ocassions throughout the year. Although sex ratios of the broods are balanced, adult populations tend to be largely female as males appear to suffer higher rates of mortality due to a greater susceptibility to predators and disease as a consequence of their showy breeding dress and a life spent largely in a frenzy of breeding. There is no parental care exhibited by this species.

Largemouth bass are among numerous predators that feed on sailfin mollies. Image © U.S.Department of Agriculture.

Sailfin mollies are small, numerous members of the lower end of the food chain. As such they are prey for numerous animals including aquatic insects, other fishes, reptiles and amphibians, birds and mammals. Specific examples of such creatures include, giant water bugs (Belostomatidae), largemouth bass (Micropterus salmoides), American alligator (Alligator mississippiensis), bullfrog (Rana catesbeiana), snowy egret (Egretta thula), and racoon (Procyon lotor).Parasites
The haploplorid trematode, Saccocoelioides sogandaresi is a known parasite of the sailfin molly.


The sailfin molly was originally described in 1821 as Mollienesia latipinna by the naturalist Charles Alexandre Lesueur, oft noted as one of a number of persons instrumental in the founding of a well known experimental settlement at New Harmony, Indiana during the 1820’s. Lesueur based his description of the sailfin molly upon specimens from freshwater ponds in the vicinity of New Orleans, Louisiana. However, Lesueur described other collections of the sailfin molly as Mollienesia multilineata in 1821, the same year in which he described M. latipinna. This conflict created confusion and eventually necessitated a ruling by the International Commission on Zoological Nomenclature (ICZN). In 1959, the ICZN placed precedence on the name Mollienesia latipinna Lesueur 1821.

A number of other synonyms exist, most of which are based on specimens from other areas of the sailfin molly’s rather large native range. These include Limia poeciloides Girard 1858, Poecilia lineolata Girard 1858, and Limia matamorensisGirard 1859. In a landmark work on poeciliid fishes, Donn Rosen and Reeve Bailey (1959) noted the priority of PoeciliaBloch and Schneider 1801 with regards to Mollienesia Lesueur 1821, thereby relegating Mollienesia to the synonymy of Poecilia. Consequently, the proper binomial for the sailfin molly is Poecilia latipinna (Lesueur, 1821).

Implications for fisheries management

Etelis boweni (top photo) looks nearly identical to another species, Etelis carbunculus (bottom photo). (Photo credit: Wakefield et al. 2014)

John (Jack) Randall, a world-renowned fish taxonomist from Hawaiʻi who passed away in April 2020, was part of the research team that made the discovery. This new journal article would have added to more than 900 papers published by Randall over his lifetime. The team was led by Kim Andrews from the University of Idaho, and also included Iria Fernandez-Silva from the University of Vigo in Spain, both former UH postdoctoral researchers who studied under Bowen and fish taxonomist Hans Ho from the National Museum of Marine Biology and Aquarium in Taiwan. The original suggestion for the species name came from a former UH Mānoa PhD student of Bowen, Michelle Gaither, who is now at the University of Central Florida.

&ldquoThe discovery of the new species has important implications for fisheries management, especially in areas where both species occur together, since it’s important for different species to be managed separately,&rdquo said Andrews.

Gnathostomes: Jawed Fishes

Gnathostomes, jawed vertebrates, can be divided into two types of fish: Chondrichthyes (cartilaginous fish) or Osteichthyes (bony fish).

Learning Objectives

Differentiate among the types of jawed fishes

Key Takeaways

Key Points

  • Early jawed fish (gnathostomes) were able to exploit new nutrient sources because of their jaws and paired fins.
  • Chondrichthyes includes all jawed fish with cartilagenous skeletons, such as sharks, rays, skates, and chimaeras.
  • Osteichthyes includes all jawed fish with ossified (bony) skeletons this includes the majority of modern fish.
  • Osteichthyes can be further separated into Actinopterygii (the ray-finned fishes) and Sarcopterygii (lobe-finned fishes).
  • The majority of modern fish species are actinopterygii, from trout to clownfish.
  • Early Sarcopterygii (lobe-finned fishes) evolved into modern tetrapods, including reptiles, amphibians, birds, and mammals.

Key Terms

  • ossified: composed of bone, which is a calcium phosphate matrix created by special cells called osteoblasts
  • operculum: a covering flap or lidlike structure in plants and animals, such as a gill cover
  • Chondrichthyes: a taxonomic class within the subphylum Vertebrata: the cartilaginous fish
  • Osteichthyes: a taxonomic class within the subphylum vertebrata: the bony fish

Gnathostomes: Jawed Fishes

Gnathostomes or “jaw-mouths” are vertebrates that possess jaws. One of the most significant developments in early vertebrate evolution was the development of the jaw, which is a hinged structure attached to the cranium that allows an animal to grasp and tear its food. The evolution of jaws allowed early gnathostomes to exploit food resources that were unavailable to the jawless animals. In early evolutionary history, there were gnathostomes (jawed fishes) and agnathans (jawless fishes). Gnathostomes later evolved into all tetrapods (animals with four limbs) including amphibians, birds, and mammals.

Early gnathostomes were jawed fishes that possessed two sets of paired fins, which increased their ability to maneuver accurately. These paired fins were pectoral fins, located on the anterior body, and pelvic fins, on the posterior. The evolution of the jaw combined with paired fins permitted gnathostomes to expand from the sedentary suspension feeding of jawless fishes and become mobile predators. The gnathostomes’ ability to exploit new nutrient sources led to their evolutionary success during the Devonian period. Two early groups of gnathostomes were the acanthodians and placoderms, which arose in the late Silurian period and are now extinct. Most modern gnathostomes belong to the clades Chondrichthyes and Osteichthyes.

Placoderms: Dunkleosteous was an enormous placoderm from the Devonian period, 380–360 million years ago. It measured up to 10 meters in length and weighed up to 3.6 tons. As gnathostomes, they were more mobile and could exploit more food resources than the agnathostomes.

Chondrichthyes: Cartilaginous Fishes

The clade Chondrichthyes consists of sharks, rays, and skates, together with sawfishes and a few dozen species of fishes called chimaeras, or “ghost,” sharks. Chondrichthyes are jawed fishes that possess paired fins and a skeleton made of cartilage. This clade arose approximately 370 million years ago in the early or middle Devonian.

Hammerhead shark: Hammerhead sharks tend to school during the day and hunt prey at night. As members of Chondrichthyes, their skeletons are composed of cartilage.

Most cartilaginous fishes live in marine habitats, although a few species live in fresh water for part or all of their lives. Most sharks are carnivores that feed on live prey, either swallowing it whole or using their jaws and teeth to tear it into smaller pieces. Shark teeth probably evolved from the jagged scales that cover their skin called placoid scales. Some species of sharks and rays are suspension feeders that feed on plankton.

Sharks have well-developed sense organs that aid them in locating prey, including a keen sense of smell and electroreception. Organs called ampullae of Lorenzini enable sharks to detect the electromagnetic fields that are produced by all living things, including their prey. Only aquatic or amphibious animals possess electroreception. Sharks, together with most fishes and aquatic and larval amphibians, also have a sense organ called the lateral line, which is used to detect movement and vibration in the surrounding water. It is often considered homologous to “hearing” in terrestrial vertebrates. The lateral line is visible as a darker stripe that runs along the length of a fish’s body.

Rays and skates comprise more than 500 species and are closely related to sharks. They can be distinguished from sharks by their flattened bodies, pectoral fins that are enlarged and fused to the head, and gill slits on their ventral surface. Like sharks, rays and skates have a cartilaginous skeleton. Most species are marine and live on the sea floor, with nearly a worldwide distribution.

Osteichthyes: Bony Fishes

Members of the clade Osteichthyes, also called bony fish, are characterized by a bony skeleton. The vast majority of present-day fish belong to this group, which consists of approximately 30,000 species, making it the largest class of vertebrates in existence today.

Nearly all bony fish have an ossified skeleton with specialized bone cells (osteocytes) that produce and maintain a calcium phosphate matrix. A few groups of Osteichthyes, such as sturgeons and paddlefish, have primarily cartilaginous skeletons, but retain some bony elements. The skin of bony fish is often covered by overlapping scales. Skin glands secrete mucus that reduces drag when swimming and aids the fish in osmoregulation. Like sharks, bony fish have a lateral line system that detects vibrations in water. All bony fish use gills for gas exchange. Water is drawn over gills that are located in chambers covered and ventilated by a protective, muscular flap called the operculum. Many bony fish also have a swim bladder, a gas-filled organ that helps to control the buoyancy of the fish.

Bony fish are further divided into two extant clades: Actinopterygii (ray-finned fish) and Sarcopterygii (lobe-finned fish). Actinopterygii, the ray-finned fish include many familiar fish, such as tuna, bass, trout, and salmon, among others. Ray-finned fish are named for their fins that are webs of skin supported by bony spines called rays. In contrast, the fins of Sarcopterygii are fleshy and lobed, supported by bone. Although most members of this clade are extinct, living members include the less-familiar lungfishes and coelacanths. Early Sarcopterygii evolved into modern tetrapods, including reptiles, amphibians, birds, and mammals.

Actinopterygii and Sarcopterygii: The (a) sockeye salmon (Actinopterygii) and (b) coelacanth (Sarcopterygii) are both bony fishes of the Osteichthyes clade. The coelacanth, sometimes called a lobe-finned fish, was thought to have gone extinct in the Late Cretaceous period, 100 million years ago, until one was discovered in 1938 near the Comoros Islands between Africa and Madagascar.

Classifying Fish Species Within Ecosystems

The NIRS analysis distinguished individual species, groups of species from individual ecosystems, and groups from combined ecosystems. It had an overall accuracy of 92 percent, 98 percent, and 100 percent, respectively.

Species Identification and Environmental Influences

The accuracy of species predictions varied depending on where they came from. Most misclassifications happened between:

  • Same species from different geographic areas (for example, red snapper in the Gulf of Mexico versus North Atlantic)
  • Different species from the same area (walleye pollock, Pacific cod, and yellowfin sole in the Bering Sea)

“These results suggest that habitat, diet, and environmental conditions such as temperature may influence the spectral signature of otoliths,” said Benson. “That suggests that NIRS may prove useful in answering ecological questions. For example, it could help us understand how ocean warming affects food webs.”

3D view of otolith NIR spectral analyses by species. GOM – U.S. Gulf of Mexico, NAO – North Atlantic Ocean, E GOM – East U.S. Gulf of Mexico, W GOM – West U.S. Gulf of Mexico. Image: NOAA Fisheries.

Ecosystems and Oceanography

NIRS discriminated otoliths of all species analyzed from the eastern Bering Sea and North Pacific Ocean large marine ecosystems with 100 percent accuracy. North Atlantic Ocean (97 percent) and Gulf of Mexico (93 percent) ecosystems were slightly more difficult to discriminate.

These results may reflect the oceanography and ecology of each region.

North Pacific Ocean currents split along the U.S. West coast and support different large marine ecosystems in the North Pacific and eastern Bering Sea. Differences between fish otoliths from the two regions may be explained in part by annual sea ice. It has a strong impact on marine chemistry and biology in the eastern Bering Sea, but not on the North Pacific Ocean.

Gulf of Mexico water is transported north along the Atlantic coast of the United States by the Gulf Stream. Around Cape Hatteras, the Gulf Stream swings away from the coast. There it creates a boundary between the Gulf of Mexico and North Atlantic Ocean ecosystems. Fish and fauna are known to move across in both directions.

3D view of otolith NIR spectral analyses by regions. EBS – Eastern Bering Sea, GOM – U.S. Gulf of Mexico, NAO – North Atlantic Ocean, NPO – North Pacific Ocean. Image: NOAA Fisheries.

Classification of Fish

There are about 28,000 existing species of fish, and they are placed in five different classes. The classes are commonly referred to as hagfish, lampreys, cartilaginous fish, ray-finned fish, and lobe-finned fish (see the table in the previous lesson).


Hagfish are very primitive fish. They retain their notochord throughout life rather than developing a backbone, and they lack scales and fins. They are classified as vertebrates mainly because they have a cranium. Hagfish are noted for secreting large amounts of thick, slimy mucus. The mucus makes them slippery, so they can slip out of the jaws of predators.


Like hagfish, lampreys also lack scales, but they have fins and a partial backbone. The most striking feature of lampreys is a large round sucker, lined with teeth, that surrounds the mouth (see Figure below). Lampreys use their sucker to feed on the blood of other fish species.

Sucker Mouth of a Lamprey. The mouth of a lamprey is surrounded by a tooth-lined sucker.

Cartilaginous Fish

Cartilaginous fish include sharks, rays, and ratfish (see Figure below). In addition to an endoskeleton composed of cartilage, these fish have a complete backbone. They also have a relatively large brain. They can solve problems and interact with other members of their species. They are generally predators with keen senses. Cartilaginous fish lack a swim bladder. Instead, they stay afloat by using a pair of muscular fins to push down against the water and create lift.

Cartilaginous Fish. All of these fish belong to the class of cartilaginous fish with jaws. (a) Oceanic whitetip shark (b) Ray (c) Ratfish

One of the most important traits of cartilaginous fish is their jaws. Jaws allow them to bite food and break it into smaller pieces. This is a big adaptive advantage because it greatly expands the range of food sources they can consume. Jaws also make cartilaginous fish excellent predators. It you&rsquove ever seen the film Jaws, then you know that jaws make sharks very fierce predators (see also Figure below).

Jaws of a Shark. Sharks have powerful jaws with multiple rows of sharp, saw-like teeth. Most other fish are no match for these powerful predators.

Ray-Finned Fish

Ray-finned fish include the majority of living fish species, including goldfish, tuna, salmon, perch, and cod. They have a bony endoskeleton and a swim bladder. Their thin fins consist of webs of skin over flexible bony rays, or spines. The fins lack muscle, so their movements are controlled by muscles in the body wall. You can compare their ray fins with the fleshy fins of lobe-finned fish in Figure below.

Fins of Bony Fish. The fins of ray-finned and lobe-finned fish are quite different. How is the form of the fins related to their different functions in the two classes of fish? Ray Fin (left), Lobe Fin (right)

Lobe-Finned Fish

Lobe-finned fish are currently far fewer in number than ray-finned fish. Their fins, like the one shown in Figure above, contain a stump-like appendage of bone and muscle. There are two groups of lobe-finned fish still alive today: coelacanths and lungfish.

Fish Reproduction and Development

Nearly all fish reproduce sexually, and most species have separate sexes. Those without separate sexes avoid self-fertilization by producing sperm and eggs at different times. Each fish typically produces a large number of gametes. In most fish species, fertilization takes place externally. These fish are oviparous. Eggs are laid and embryos develop outside the mother&rsquos body. In a minority of fish, including sharks, eggs develop inside the mother&rsquos body but without nourishment from the mother. These fish are ovoviviparous.


In many species of fish, a large group of adults come together to release their gametes into the water at the same time. This is called spawning. It increases the chances that fertilization will take place. It also means that many embryos will form at once, which helps ensure that at least some of them will be able to escape predators.

With spawning, there is no way for fish parents to know which embryos are their own. Therefore, fish generally don&rsquot provide any care to their eggs or offspring. There are some exceptions, however, including the fish described in Figure below, which is performing mouth brooding.

Mouth Brooding. Some species of fish carry their fertilized eggs in their mouth until they hatch. This is called mouth brooding. If you look closely, you can see the eggs inside the mouth of the cardinalfish pictured here.

Fish Larvae

Fish eggs hatch into larvae that are different from the adult form of the species (see Figure below). A larva swims attached to a large yolk sac, which provides the larva with food. The larva eventually goes through metamorphosis and changes into the adult form. However, it still needs to mature before it can reproduce.

Salmon Larva. This newly hatched salmon larva doesn&rsquot look very fish-like. The structure hanging from the larva is the yolk sac.

Interesting Insights from the Oscar Fish!

While the oscar is a commonly kept aquarium fish, many owners are not aware of the amazing biological concepts their fish displays. In fact, the oscar is a perfect example of the following concepts!

Suction Feeding

Oscar fish – like many other predatory fish – use the viscosity of water to their advantage. Unlike air, which moves freely around objects, water is much denser. Plus, water molecules pull on each other through the process of cohesion. So, when the oscar opens its mouth quickly, a massive wall of water is sucked in.

Smaller fish unlucky enough to be caught in the wave are pulled into the oscar’s mouth, with no hope of escaping. Besides fish, many other aquatic organisms use suction feeding to their advantage. Notable suction feeders include some species of shark, newts, catfish, and many others. Suction feeders are typically “ambush predators” – waiting carefully for their prey to come close enough to be caught in the suction vortex!

Invasive Aquarium Fish

The oscar fish is not the only fish that has expanded its range since it has been commonly kept as an aquarium species. Unfortunately, the aquarium industry has introduced many invasive species into natural environments around the world. While the environmental impact of oscar fish releases has not been well studied, other aquarium species that have been released are wreaking havoc on natural environments.

For example, the Zebrafish is a commonly kept saltwater aquarium species. The fish is beautiful, colorful, and very interesting to watch in captivity. For this reason, the fish was imported to the United States from its native range in the Indian Ocean. However, a few Zebrafish were accidentally released into the Gulf of Mexico. Only a few decades later, the Zebrafish has become a massively destructive species along many reefs in the Gulf.

Since the Zebrafish is a voracious predator and has a number of protective spines, it can eat almost everything and has no natural predators in the Gulf of Mexico. As such, Zebrafish populations have exploded and are rapidly depleting many fish species important to the health of the coral reef. In fact, this invasive species is so destructive that is has been partially blamed for the loss of corals from South America to Florida.

Brood Care

Though the oscar is a voracious predator, these fish can also make very protective parents. Oscar fish naturally defend their territory, chasing off all other fish that come too close and eating anything small enough to fit in their large mouths!

However, when it comes to their babies, oscars are very careful. In fact, the oscar fish will protect its babies and is very careful not to suck them up. This is known as “brood care” and is a type of parental care seen in several fish species. While most fish simply release their eggs into the environment, the oscar will protect its offspring until they are large enough to leave and established their own territory.


  1. Guk

    This rather good phrase is necessary just by the way

  2. Jukazahn

    In this all the charm!

  3. Zushakar

    And what is the result?

  4. Corey

    I like this topic

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