Fish Biology, Anatomy and Identification of Cultivable Species
This domain examines external and internal fish anatomy needed for identification: body shape, fins, mouth, barbels, scales, gills, swim bladder and digestive tract. The exam often asks you to separate Indian major carps from exotic carps and to link structure with feeding habit.
Core rules
- Body regions: head, trunk and tail; median fins are dorsal, anal and caudal; paired fins are pectoral and pelvic.
- Mouth position indicates feeding zone: upturned or superior for surface feeding, terminal for mid-water, inferior for bottom feeding.
- Gills exchange gases; gill rakers strain plankton. Swim bladder controls buoyancy. Scale type and lateral line help identify species.
- Catla: deep body, large head, upturned mouth, no barbels, surface feeder.
- Rohu: elongated body, terminal mouth, mid-water feeder. Mrigal: slender, inferior mouth, bottom feeder.
- Exotic carps: silver carp has a large head and upturned mouth; grass carp is cylindrical and feeds on macrophytes; common carp has barbels and bottom-feeding habit.
Worked example
A fish has a very deep body, a large head, an upturned mouth and no barbels. Identify it. Reasoning: deep body and large head point to catla; the upturned mouth places it as a surface feeder; absence of barbels separates it from common carp. The answer is catla, not rohu, because rohu is more elongated with a terminal mouth.
Traps
Do not identify carps by colour alone; body depth, mouth and barbels are more reliable. Do not confuse grass carp with silver carp: grass carp is cylindrical and eats plants, silver carp is deep-bodied and filters plankton. Do not call the swim bladder a digestive organ.