Fish Seed Production, Hatchery and Nursery Management
Why hatchery seed dominates
Riverine seed collection is unreliable, mixed and carries wild pathogens, so induced breeding supplies almost all carp seed in Odisha. Brood stock of 1-2 kg is reared in separate ponds, fed oil cake and rice bran with periodic injection of vitamins, and selected so that the female is visibly gravid and the male oozes milt on gentle pressure. A 1:2 male to female ratio is usual.
The sequence of operations
- Hypophysation: pituitary gland extract or a synthetic inducing agent is injected. Common protocols use a split dose in the female, about 2-3 mg/kg as the first dose and a resolving dose of 5-8 mg/kg, and a single 2-3 mg/kg dose in the male; synthetic agents are dosed by volume per kg as per the manufacturer, so quote the range and the protocol you were taught.
- After the latent period (about 6-8 hours at 26-28 degrees C) eggs are stripped into a dry tray and milt is added, mixed with a feather, and water is added to activate sperm, giving dry-method fertilisation.
- Incubation in a Chinese circular hatchery or glass jar hatchery; hatching takes roughly 18-24 hours at 26-28 degrees C. Spawn are 3-6 mm, fry 20-25 mm and fingerlings 80-100 mm.
- Nursery: 0.05-0.1 ha pond, spawn stocked at about 3-5 million per hectare, reared 10-15 days on yolk and then plankton; then fry are transferred to rearing ponds at lower density to become fingerlings.
Worked example
A 2 kg female is injected at 3 mg/kg of pituitary extract: 2 x 3 = 6 mg of extract. She yields 1,20,000 eggs. With 85% fertilisation and 75% hatching, spawn recovered = 1,20,000 x 0.85 x 0.75 = 76,500. Always multiply the two rates; never stop at the egg count.
Traps that cost marks
- Confusing spawn, fry and fingerling sizes and the ponds used for each.
- Forgetting that both fertilisation and hatching rates reduce the recoverable number.