Instruct: Given a question, retrieve relevant documents that answer the question.
Query: How many species of fish have been identified?
Fish are very diverse animals and can be categorised in many ways. This article is an overview of some of ways in which fish are categorised. Although most fish species have probably been discovered and described, about 250 new ones are still discovered every year. According to FishBase, 33,100 species of fish had been described by April 2015.[5] That is more than the combined total of all other vertebrate species: mammals, amphibians, reptiles and birds.
The following non-native species have been introduced into park waters, many of which were barren of fish. In many cases, these non-native species, when introduced into waters with native species have severely impacted the original range of native species.
Falcaustra tannaensis is the 87th discovered species of the nematode genus "Falcaustra". It has been identified in geckos from Tanna Island, Vanuatu. Species of "Falcaustra" have been known parasites that occur in the digestive tracts of fish, amphibians, and mammals. Until 2010, none had ever been identified in the South Pacific Islands.
The fishing industry on Dal is the second largest industry in the region and is central to many of the people's livelihoods who reside on the lake's periphery. Dal's commercial fisheries are particularly reliant on carp fish species, which were introduced into the lake in 1957. As a result, carp constitutes 70% of all the fish caught in the lake while the schizothonax constitutes 20% and other species account for 10%. Fishermen use a locally manufactured cast net which comprises six parts with a diameter of 6 metres. It is operated from a wooden fishing boat made out of deodar, typically 20ftx4ft in size. The gradual decline in quality of the lake water through pollution has resulted in lower fish stocks and the extinction of endemic varieties of fish. The causes for such deterioration have been identified and remedial actions have been initiated.The various fishing nets being used in Dal are cast net (Zaal/Duph), Long line (Walruz), Gill net (Pachi, Shaitan zaal), Rod and line (Bislai), Scoop net (Attha zaal) (Bhat et al., 2008)
Reptiles and amphibians are only an occasionally contributor to the diet in many regions. Most of the 30 or so species recorded have been taken as supplemental prey in Spain, i.e. several lizards (including geckos), frogs and toads, snakes and, to a lesser degree, turtles.[20][25][41][42] One species widely and commonly reported in Europe outside of the Iberian region is the 23g (0.81oz) common frog (Rana temporaria). It was the leading prey, making up 45% of the prey found at nests in Rogaland, Norway.[106] Also, the common frog was the second most abundant prey species in studies from southern Sweden, Valais and Engadin in Switzerland, Verbano-Cusi-Ossola, Italy and an enormous study from Slovakia, in the latter 10,476 frogs recorded making up 28.2% of the prey.[28][56][94][107][108] There are no records of vicious fights between snakes and Eurasian eagle-owls as there are with the great horned owl, with the horned owl sometimes losing its life after attacking a snake. Perhaps with their larger size and greater power, the eagle-owl can more easily overpower any snakes they encounter, although most snakes in Europe and temperate Asia are not particularly large.[109][110] Like the golden eagle, the eagle-owl may attack spur-thighed tortoises (Testudo graeca). In Lebanon, a “large adult” tortoise, which would be at least as heavy as the eagle-owl itself, was among their food items, although how they handle and eat this large, hard-shelled prey is not clear.[74][96] Eurasian eagle-owls also opportunistically prey on fish, although never in large numbers, as fish are likely to be taken incidentally while hunting for other prey such as water birds. This species is known to take a greater diversity of fish (more than 30 species verified) and is more widely reported to hunt them than the great horned owl. Most of the fish recorded are medium-sized, with at least 10 each of various kinds of carp or cod, but several species averaging more than 2,000g (4.4lb) in mature mass have been taken, including common barbell (Barbus barbus), common carp (Cyprinus carpio), northern pike (Esox lucius) and a few species of trout, even bigger marine predators like the anglerfish (Lophius piscatorius) and European conger (Conger conger). However, in many cases small, young specimens may be caught of these large fish species rather than full-grown adults.[14][111] Several species of insect and invertebrate have been identified in eagle-owl pellets. In some cases, these may be undigested insects in the stomachs of birds eaten by the eagle-owl but Eurasian eagle-owls have been verified as actively hunting insects and aquatic invertebrates such as snails and crabs before.[2] Especially diverse in the diet are ground-based beetles, at least 20 species have been identified mainly those in the Carabus (ground beetle) genus.[27]
The scales of these fishes are thinner, flexible scales called bony-ridged scales. Blackchins have scales called cycloid scales, which are round and, compared to the scales of other fishes, smooth. These scales are a clue that this species is primitive in comparison to other teleosts, many of whom have ctenoid scales. For species of fish with either version of leptoid scales, the age of the fish can be determined by examining the pattern of ridges on a scale, similar to how tree trunk rings display the age of a tree.
A total of 14 species of marine mammals have been identified in the surrounding waters: elephant seal, fur seal and sea lions all breed on the islands with the largest elephant seal breeding site has over 500 animals. A total of 227 bird species have been seen on the islands, over 60 of which are known to breed on the islands. There are two endemic species and 14 endemic subspecies of bird. Five penguin species including the Magellanic penguin breed on the islands as do over 60% of the global black-browed albatross population.
There are no native reptiles or amphibians on the islands. Over 200 species of insects have been recorded, along with 43 spider species and 12 worm species. Only 13 terrestrial invertebrates are recognised as endemic, although information on many species is lacking and it is suspected up to two thirds of species found are actually endemic. Due to the island environment, many insect species have developed reduced or absent wings. There are around 129 freshwater invertebrates, the majority being rotifer; however, the identification of some species remains in dispute. Six species of fish are found in freshwater areas, including zebra trout and falklands minnows.
A total of 202 different birds have been recorded on the island. Eighteen species of land birds breed on the island and there are many more migratory species that occur on the island and its adjacent islets, many tame enough that it is possible for humans to get quite close. The island has been identified by BirdLife International as an Endemic Bird Area, and the Permanent Park Preserve as an Important Bird Area, because it supports the entire population of Lord Howe woodhens, most of the breeding population of providence petrels, over 1% of the world population of another five seabird species, and the whole populations of three endemic subspecies.
The shapes and proportional sizes of the otoliths vary with fish species. In general, fish from highly structured habitats such as reefs or rocky bottoms (e.g. snappers, groupers, many drums and croakers) will have larger otoliths than fish that spend most of their time swimming at high speed in straight lines in the open ocean (e.g. tuna, mackerel, dolphinfish). Flying fish have unusually large otoliths, possibly due to their need for balance when launching themselves out of the water to "fly" in the air. Often, the fish species can be identified from distinct morphological characteristics of an isolated otolith.
Habitat diversity on Refuge lands provides for the needs of resident wildlife species as well as numerous seasonal residents and migrants of the Pacific Flyway. Over 400 bird species have been recorded at the Refuge and at least 93 species have nested on the Refuge. In addition, 41 species of mammals, 18 species of reptiles, 4 species of amphibians and 15 species of fish have been identified in the area.
Marine species flourish at times when the bar is open such blue manna crabs, juvenile prawns, cockles and mussels have all been identified in the inlet. 
Many fish species inhabit the estuary such as the common minnow, hardyheads, gobies and larger species such as Black Bream and Sea Mullet.
Two large man-made lakes were excavated for the development and a ridge was created from the earth that was removed. The lakes are simply named East Lake and West Lake. While no fish have been stocked in either lake, because they drain out to the Red River through underground pipes, fish have made their way into the lakes. Brown bullhead, carp and northern pike are some of the species of fish that have been identified in the lakes. The lakes are also a popular hangout for Canada geese, pelicans, mallard ducks, coots, and other assorted fowl, many of which come to Whyte Ridge from the nearby FortWhyte Alive Wildlife Centre.
Due in part to its prevalence in the exotic pet trade, Florida has a large number of non-native species. The Florida Fish and Wildlife Commission tracks 31 species of mammals, 196 species of birds, 48 species of reptiles, 4 species of amphibians, and 55 species of fish that have been observed in the state. Many of the identified species are either non-breeding or stable populations, but several species, including the Cane Toad ("Bufo marinus"), Gambian Pouched Rat ("Cricetomys gambianus"), Nile monitor ("Varanus niloticus"), and Burmese Python ("Python molurus bivittatus"), have created significant impact on the delicate ecosystems of the state, especially in the tropical southern third of the state.
In Ireland, catch and release has been used as a conservation tool for Atlantic salmon and sea trout fisheries since 2003. A number of fisheries now have mandatory catch and release regulations. Catch and release for coarse fish has been used by sport anglers for as long as these species have been fished for on this island. However catch and release for Atlantic salmon has required a huge turn about in how many anglers viewed the salmon angling resource. To encourage anglers to practice catch and release in all fisheries a number of government led incentives have been implemented.
The marine environment of the Kogatapu includes reef, lagoon, channel and ocean; and are home to many species of fish, corals, algae and invertebrates. Surveys prior to 1999 identified 76 species of indicator fish, 141 species of food fish and 149 mobile invertebrates such as crabs and sea cucumbers. A 2007 survey established that fish populations had increased as a result of the Funafuti Conservation Area. Large-sized individual fishes of the highly prized target food species, such as grouper and snapper were observed; the presence of so many large fish of desirable target food species indicates that there is very low fishing pressure in the Funafuti Conservation Area, although enforcement by conservation rangers of the no-fishing rules is necessary to preserve the fish stock.
Little is known about the life cycle or biology of "Microsynodontis." Identifying an individual fish's species within the genus of Microsynodontis can be difficult, but some diagnostic methods have been identifying, including the identification of the color and color patterns, the shape and size of the fins, the shape and size of the snout, the characteristics of the spines of the fish, and the characteristics of the tubercles, which are small, rounded protrusions on the skin of the fish. The number of teeth in an individual has not been demonstrated to be useful in identifying the species in this genus, unlike in other genera of the Mochokidae.
Turneffe is home to many marine species that are threatened and/or commercially important. The land and seascape consists of a network of highly productive flats, creeks, and lagoons dotted by more than 150 mangrove islands and higher cayes with savanna and littoral forest. Large expanses of intact mangrove and seagrass habitat and shallows provide important nursery functionality for a wide array of fish species, crocodiles, lobster, conch and other invertebrates. It is home to more than 500 species of fish, 65 species of stony corals, sea turtles, manatees, dolphins, seabirds, and other wildlife. In addition, at least three known important fish spawning aggregation sites have been identified.
Vegetation is mostly lowland forest and "campina".
There is dry land tropical forest with dense or open coverage, as well as periodically flooded alluvial forest.
The forest has many species of palm trees and vines.
130 species of mammals have been recorded including 16 primate species, jaguar, puma, giant otter, tapir, deer and manatee. 
Reptiles include caimans and alligator. There 84 species of amphibians and 115 of fish.
527 species of birds have been identified including macaws, parrots, herons and the harpy eagle.
Protected species include the "Paititia neglecta" butterfly.
The Philippine Sea has a marine territorial scope of over , and an EEZ of 2.2 million km. Attributed to an extensive vicariance and island integrations, the Philippines contains the highest number of marine species per unit area relative to the countries within the Indo-Malay-Philippines Archipelago, and has been identified as the epicenter of marine biodiversity. With its inclusion in the Coral Triangle, the Philippine Sea encompasses over 3,212 fish species, 486 coral species, 800 seaweed species, and 820 benthic algae species, wherein the Verde Island Passage is dubbed as “the center of the center of marine fish biodiversity”. Within its territory, thirty-three endemic species of fish have been identified, including the blue-spotted angelfish (Chaetodontoplus caeruleopunctatus) and the sea catfish (Arius manillensis). The Philippine marine territory has also become a breeding and feeding ground for endangered marine species, such as the whale shark (Rhincodon typus), the dugong (Dugong dugon), and the megamouth shark (Megachasma pelagios).
The "Z. varolai" specimen from the Pietra Leccese Formation dates back to the Tortonian Age of the Late Miocene Epoch, around 11.6 to 7.2 million years ago (mya), and most likely inhabited the Paratethys Sea. This formation has also unearthed the remains of several other large vertebrate species. Ancient sirenians of the genus "Metaxytherium" were apparently common throughout the ancient Mediterranean sea. Many fish remains of teleost fish, rays, and at least twenty species of sharks have been discovered, such as the tiger shark ("Galeocerdo cuvier") and the extinct "Carcharocles megalodon". Three species of turtles have been identified: "Trachyaspis lardyi", "Procolpochelys melii", which are both ancient marine turtles, and "Psephophorus polygonus", an ancient leatherback sea turtle. Aside from "Z. varolai", two other cetacean species have been described from this formation: the oldest known gray whale "Archaeschrichtius ruggieroi", and a species of beaked whale "Messapicetus longirostris".
The waters of the Cahaba are home to more than 131 species of freshwater fishes (18 of which have been found in no other river system), 40 species of mussels, and 35 species of snails. The river has more fish species than can be found in all bodies of water in California. Sixty-nine of these animal species are endangered. The endemic freshwater snail "Elimia cahawbensis" is named after the river. One species long thought to be extinct, "Leptoxis compacta", the Oblong rocksnail, was rediscovered in the Cahaba in 2011. Due to damming for hydropower, pollution, transportation, and erosion, it has suffered losses of species. Almost a quarter of the original documented mussel species in the Cahaba have disappeared with similar trends in the fish and snail numbers of species. Many species have still been discovered and rediscovered in and on the surrounding region of the river. The Cahaba is also home to 13 snail species not found anywhere else in the world. In the early 21st century, a Georgia botanist Jim Allison discovered eight unknown flower species, and later eight more were identified along the river's course that previously had not been sited in the state of Alabama. This region is most noted for containing numerous species of mollusks and snails. These species feed other aquatic dwelling animals, improve water quality by eating algae, and even indicate environmental issues due to their receptiveness of pollution. Fourteen of the freshwater fish species are non-native species in the Cahaba River.
Predators of marine bryozoans include nudibranchs (sea slugs), fish, sea urchins, pycnogonids, crustaceans, mites and starfish. Freshwater bryozoans are preyed on by snails, insects, and fish. In Thailand, many populations of one freshwater species have been wiped out by an introduced species of snail. A fast-growing invasive bryozoan off the northeast and northwest coasts of the US has reduced kelp forests so much that it has affected local fish and invertebrate populations. Bryozoans have spread diseases to fish farms and fishermen. Chemicals extracted from a marine bryozoan species have been investigated for treatment of cancer and Alzheimer's disease, but analyses have not been encouraging.
The saltwater fish of Romania are the Black Sea species of fish that live in the territorial waters of Romania. A 2005 biodiversity inventory of the Romanian waters identified around 140 species and subspecies of marine fish. Many of the species have seen their stocks plummet in the last 50 years due to commercial exploitation. The six species that are the most commercially viable today are all small-sized fish: the red mullet, the sand smelt, the round goby, the European anchovy, the merling and the sprat. According to recent reports, dozens of species of fish that were believed to be extinct in the Black Sea have reappeared in the area in the last few years, most likely travelling from the Mediterranean, due to the improved water quality and regeneration of the Black Sea ecosystem.
Israel contains many invasive species brought by man, including scores of molluscs (the most common is the common garden snail "Helix aspersa") which usually live around gardens and greenhouses but also in natural habitats of native molluscs. As of 2008, over 220 species of invasive insects have been identified, some of them considered pests. The situation is little better with vertebrates, as a 2004 report reported that there are two mammalian invasive species (the coypu and Indian palm squirrel), one fish species (mosquito fish), two reptilian species (the red-eared pond slider and the roughtail gecko) as well as 18 bird species. There are no amphibian invasive species, most likely due to the fact there are no suitable habitats for such.
Fish species and the development of fisheries in Lugu Lake have been researched during 2001, 2002 and 2004. The studies reported that there are now 12 fish species in Lugu Lake, which belong to 10 genera, four families and three orders. Changes to the proliferation of fish in the lake has been due to the deposition of silt in the lake following heavy deforestation of lake's catchment. In addition to the four endemic species, eight exotic species were identified and these dominate the fish population in the lake to the detriment of the endemic species. Fishing is normally carried out using gillnets. The nets are spread over the lake’s entire length and width at different depths with mesh size varying to suit needs; they are usually spread from late afternoon to the morning hours of the following day. The eight exotic species, introduced to the lake in 1958 as part of commercial fishing activity, dominate the fishing resources of the lake, and three of the native species have been declared endangered. As a result of commercial fishing activity, the fish resources initially netted amounted to 500 tonnes. However, overfishing in the last few decades by trawlers has resulted in a drastic decline of the yield and in 1980 it was reported to be only 30 tonnes. The main reasons attributed for this decline are the heavy deforestation that occurred once in 1970 and then again between 1980 and 1990, which caused heavy siltation of the lake; the siltation advanced into the lake causing destruction of many spawning grounds of the three "Schizothorax" fishes, followed by the decrease of their stocks. Another reason given for the decrease in endemic fish stocks is the introduction of the exotic species, which has led to a decline in the indigenous "Schizothoracid" species.