Rohu induced breeding fails after the second pituitary dose
A hatchery near Raigad has 18 female rohu (1.2–1.8 kg) and 22 males. Staff select females with a soft, distended abdomen; several release a few eggs when handled. At 18:00 they inject females with 2 mg/kg carp pituitary extract; at 00:00 they give a second dose of 6 mg/kg. Males receive no injection. The spawning tank is at 23–24°C because of a cold spell. By 10:00 the next day no fish has spawned; two females are lethargic and later die. Visitors have been walking around the tank and staff have netted the fish twice to check for eggs. The hatchery owner wants to strip all females immediately and add urea to the tank to 'increase plankton and oxygen'.
1. Was the failure mainly due to temperature, broodstock handling, or injection protocol? Justify your ranking.
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All three contributed, but the most important management faults are handling stress and an incomplete injection protocol.
- Temperature: 23–24°C is below the usual 26–28°C range for carp breeding. Cooler water slows maturation and lengthens the time from the second dose to spawning. Ten hours after the second dose may still be within a delayed window, so temperature is a contributing factor rather than proof of failure.
- Handling: The females were netted twice, visitors disturbed the tank, and several released eggs on handling. This suggests over-ripe broodstock and stress. Repeated netting can block spawning and cause injury or death.
- Injection protocol: Males received no injection at all. Males normally need a small dose at the appropriate time to produce milt. Without ready males, even ovulated females may not spawn successfully.
The ranking is therefore: handling/over-ripeness and missing male injection first, low temperature second. The two deaths point to stress and injury, not to a simple dose failure.
2. Should the owner strip the females now? What checks would you make before deciding?
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Do not strip all females immediately. Forced stripping of non-ovulated fish causes injury, egg retention and death. First check:
- Gently press the abdomen. If eggs flow freely and are transparent, uniform and not watery, the fish is ovulated and stripping may be possible within a short window.
- If eggs are clumped, opaque, bloody or released only with hard pressure, the fish is not ready or is over-ripe; return it to quiet water and do not strip.
- Check males for flowing milt. Without good milt, stripping females is pointless.
- Check water temperature and dissolved oxygen; correct temperature to 26–28°C and keep the tank quiet and shaded.
If a few females are truly free-flowing, strip them gently into a dry bowl, fertilise immediately with fresh milt, and incubate. Do not add urea to the spawning tank; it is a fertilizer, not an oxygen source, and can worsen water quality.
3. Outline a corrected protocol for the next breeding batch.
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A corrected protocol should cover broodstock, temperature, sex ratio, injection and quiet handling:
- Select fully ripe females with a soft abdomen and a visible genital papilla, but reject fish that leak eggs on gentle handling.
- Hold brooders in clean, well-oxygenated water at 26–28°C for at least a few hours before injection; avoid cold shock.
- Use a sex ratio of about 1:1 to 2:1 male:female and inject males with the appropriate small dose at the time of the female's second dose.
- Give the standard two-dose pituitary schedule based on body weight, but do not exceed the recommended dose. Record times and weights.
- Keep the spawning tank quiet, shaded and undisturbed. Do not net fish repeatedly.
- Expect spawning after the normal latency at the actual water temperature; check only from outside the tank. Strip only free-flowing eggs.
- Have a backup: if spawning fails, do not reuse the same over-ripe fish; improve broodstock conditioning and water temperature for the next batch.