Aquatic Ecology Course Zoo 374

Fins and their modifications Types:- Paired (pectoral, pelvic) Unpaired (dorsal, anal, caudal) 1)Dorsal fin: used to facilitate its advance in water. * Anguilla sp., poisonous fish, spiny-rayed fish, soft-rayed fish, remora, rays, bottom fish.

2) Pelvic fin: making balance, generally behind the pectoral fin but there are some modifications (change position). * Anguilla sp., gobia, rays. 3) Pectoral fin: making balance and sometimes for advancing. Rarely change the position. * Trigla sp., Exocoetus sp.

4) Anal fin: present between anus and caudal fin. Used for up and down movement and defense. No change in position. * Pipe fish, freshwater species, eel. 5) Caudal fin: consists of 2 lobes (epicaudal and hypocaudal), help in movement “peduncle”, no spines. * eel, hippocampus.

How does the fish move? 1)Fins…..slow movement. 2)Muscles or myotomes……contraction and protraction 3)Expelling the water through respiration.

Variations in fish habitat: - The pelagic fish are those that spend most of their life in the upper layers of the water and feed mainly on plankton or other pelagic fish. - Demersal fish are those that spend most of their adult life close to the bottom, or on the bottom substrata, and feed mainly on benthic organisms. - The anadromous fish spend part of their life in salt water and migrate periodically for spawning purposes into fresh water. - The anadromous salmon can be caught on the open seas in the same areas as pelagic species.

Demersal fish They are slow moving, dorso-ventrally flattened and bottom feeding fish. The mouth is fully or slightly vented towards ventral side. The dorsal side of body is relatively dark; they are either carnivores or detritus feeders. The young spends early life at the pelagic level. Marine fish production largely depends on presence of demersal fishes. However, though they are bottom dwelling fish, only a few species live at great depths of the sea floor, and these fishes have almost no commercial importance (Demersal fish of commercial interest are mainly confined to the upper 200 m, the rest are used as a fish meal).

Those fish found living on or near the bottom of the sea. They contain little oil (1-4% fat) and called Non-oily fish e.g. cod, dogfish, haddock, halibut, plaice, saithe, skate, sole, Sea Catfish, Jewfish, Silvery Croaker, Seabream, Perch, Eel, Grouper, Silver Bream, Indian Barracuda, Black Bass, Rabbit Fish, Crab Eater, and whiting. Several species of sharks also live near the bottom and can be grouped as demersal fishes The deep-water demersal fishes are generally divided into two categories, benthic and benthopelagic. The benthic fishes are those that have a close association with the seabed and include species such as skates and flatfishes. Benthopelagic fishes are those that swim freely and habitually near the ocean floor and, in the areas where deep-water fisheries are commercially viable, they comprise most of the exploited biomass.

Milk fish Cat fish Solea sp.

Devil rays