The survey was conducted from May 2006 to December 2007 to collect different fish species available in the Khulna division. Survey sites included Bheramara, Jhenaidaha, Kaligang, Kotchandpur, Jessore, Magura, Narail, Debhata, Satkhira, Khulna and Paikgacha. Collected fish samples were taken to the laboratory of the Freshwater Sub-Station of the Bangladesh Fisheries Research Institute, Jessore. Information on origin, habitat use trophic and reproductive guilds of the collected fishes were obtained from different books (Jordan and Evermann, 1917; Hamilton, 1822; Day and Buchanan, 1877; Day, 1878; Bhuiyan, 1964; Gibson, 1978; Billard and Breton, 1979; Jayaram, 1981; Ameen, 1987; Jhingran, 1991; Khan, 1994; Jobling, 1995), from reports (Azadi, 1985; Anon., 1994; Felts et al., 1997; Hora, 1945) and from journals (Khan, 1924 and 1934; Ahmed, 1944 and 1955; Khanna, 1958; Alikunhi and Sukumaran, 1964; Doha, 1973; Balon et al., 1977; Jayaram, 1977; Johannes, 1978; Kramer, 1978; Dewan and Doha, 1979; Huda and Rahman, 1983; Austen et al., 1994; Lyons et al., 1996; Akhter and Rahman, 2008; Rahman and Akhter, 2008) while ecological classification was done according to Balon (1975 and 1981). For ecological classification the following definitions were used :
Trophic guilds: Planktivores: Mainly depend on phytoplankton and zooplankton. Diet of the adult fish of this trophic guild consists of more than 75% zooplankton and/or phytoplankton (Lyons et al., 1995). Herbivores: Primarily feed on higher aquatic plants/vegetation. Diet of the adult fish consists of more than 75% plant material (Lyons et al., 1995). Omnivores: Take all possible food materials both of plant and animal origin. Choice of food depends on availability (Lyons et al., 1995). Detritivores: Take detritus as food (Goldstein and Simon, 1999). Insectivores/Invertivores: Take all kind of insects/invertebrates as the main food (Lyons et al., 1995). Larvivores: Specialist feeders that feed on larvae of insects, fish and other organisms (Goldstein and Simon, 1999). Benthivores: Mainly feed on benthic organisms (Goldstein and Simon, 1999). Molluscivores: Specialist feeders depending on mollusks and isopods (Goldstein and Simon, 1999). Carnivores: Primarily feed on animal matters. Diet of the adult fish consists of more than 75% animal materials (Lyons et al., 1995). Parasitic: Parasitism being a form of carnivorism in which the parasite is smaller in body size than the host.
Reproductive guilds: Pelagophils/Broadcaster: Non-adhesive and non-photophobic eggs that are released and scattered in open waters, in areas where the direction of the water current is favourable for their distribution and survival. Lithopelagophils: Eggs deposited on rocks and gravel. Embryos and larvae are not photophobic (Balon et al., 1977). Lithophils: Fish spawns exclusively on gravel, rocks, stones, rubble or pebbles where their embryos and larvae develop. Embryos are highly photophobic (Balon, 1975). Phytophils: Fish scatters or deposits eggs with an adhesive membrane that sticks to submerged, live or dead aquatic plants, or to recently flooded terrestrial plants; sometimes they deposit eggs on logs and branches but never on the bottom. Embryos and larvae are not photophobic (Balon, 1975). Phytolithophils: Fish deposits eggs in relatively clear water habitats on submerged plants, if available, or on other submerged items such as logs, gravel and rocks. Embryos and larvae are photophobic. Psammophils: Fish scatter eggs directly on the clean sand/mud or near fine roots of plants that hang over sandy bottom. Eggs are small and adhesive, and the embryos are photophobic (Balon, 1975). Nest builders: Build nests with plant materials or bubbles in rocks, gravels and sand or hard bottom. Eggs are adhesive and embryos are photophobic. Guarders: Choose rocks, gravel and submerged plants for attachment of their eggs. Usually the male guard and fan the eggs but in many species both sexes are reported to guard the eggs. Mouth brooders: Incubate their eggs in the buccal cavity. Usually the male takes eggs in its mouth. Live bearers: Eggs are fertilized internally before they are expelled from the body cavity.