Induced breeding failure in a small rohu hatchery
Sunita Behera runs a 12-cistern carp hatchery at Balipatna. On 18 April she breeds rohu using 10 females of 2.0–2.5 kg and 12 males. She injects WOVA-FH at 0.3 ml/kg as the first dose and 0.6 ml/kg as the second dose 8 hours later; males receive 0.15 ml/kg with the second dose. Pond water is 26 C at 6 am, and she strips eggs 4 hours after the second injection. Only three females release eggs freely; the other seven give a few eggs mixed with blood. About 60% of the stripped eggs are unfertilised. Of the fertilised eggs only 22% hatch, and by day two the unhatched ones are covered with white cottony tufts. Total spawn is 1.8 lakh against her usual 25 lakh. The same hormone batch worked normally in March, and the cisterns were cleaned and dried a week before use.
1. Identify the likely causes of failure and match each cause to the specific observation that supports it.
Read the worked answer
The evidence points to a handling and timing failure rather than a hormone problem - the same batch worked in March, and March water is warmer.
- Stripping too early. At 26 C the interval between the second dose and ovulation in rohu is usually about 6–8 hours, not 4. Only 3 of 10 females giving eggs freely, and the rest giving a few eggs mixed with blood, is the classic signature of pressure applied before ovulation - blood comes from forcing the vent.
- Low temperature. At 26 C (versus the 27–29 C optimum) ovulation is slower and more staggered, so a fixed 4-hour rule fails. There is no evidence she checked individual females before stripping.
- Poor fertilisation (40% success). Twelve males for 10 females is adequate in number, but the males got only the second dose; if milt was not checked under a microscope for motility, or the eggs sat too long before milt was added, fertilisation falls. A dry, crowded, single-tray mixing with insufficient milt will also do it.
- Fungus on dead eggs. White cottony tufts are Saprolegnia colonising unfertilised and dead eggs. Because dead eggs were left in the incubator, the fungus spread to live eggs and also consumed oxygen, dragging the 22% hatch down further.
2. Set out a corrected breeding protocol for her next attempt, with the checkpoints and timings you would put on the hatchery wall.
Read the worked answer
Brood stock: select females with a soft, swollen abdomen and a pink, slightly protruding vent; select males that release milt on gentle pressure. Hold males and females separately until injection day and use a 2:1 male-to-female ratio in the breeding cistern.
Dose and timing: 0.3 ml/kg first dose, then 0.6 ml/kg after 8 hours; males 0.15 ml/kg at the second dose. Record the clock time of every injection.
Temperature: aim for 27–28 C by covering the cisterns or shading them. Lower the expected latency if water is warm, lengthen it if cool.
Checkpoint at 5 hours after the second dose: lift each female gently and check for free flow of eggs under light pressure. If the eggs do not flow, return her to clean, flowing water and re-check every 45–60 minutes. Never force a female that is not ovulating.
Stripping: collect eggs in a dry enamel tray, add milt from 2–3 males, mix with a feather for 30–45 seconds, add a little clean water, then wash. Keep the whole operation under five minutes.
Incubation: measure egg volume (about 1 lakh eggs per hatchery jar), keep a steady flow of 0.6–1.0 L/s, and remove dead eggs with a siphon twice a day to stop Saprolegnia spreading. Count fertilisation at 6–8 hours by sampling 100 eggs in a beaker - that single check would have told her the problem while there was still time to act.
3. Which records and quality checks should she maintain so that a failure like this is caught early next season?
Read the worked answer
A hatchery lives or dies on its register. The minimum set is:
- Brood stock register: source, weight, sex, date of selection, condition at selection.
- Injection register: hormone batch and expiry, dose per fish, exact clock time of first and second dose, water temperature at each step.
- Ovulation log: time of each check, which females flowed and which did not, latency actually achieved.
- Egg and milt log: volume of eggs stripped, number of males used, milt motility noted (even a simple 'active/inactive' note under a lens), time from stripping to mixing.
- Incubation log: eggs per jar, water flow, temperature, dead-egg removal times.
- Output log: fertilisation percentage at 6–8 hours, hatch percentage, spawn counted per cistern, and spawn sold or nursed.
The one quality check with the highest return is the 6–8 hour fertilisation sample: a poor result there allows her to adjust water flow, remove dead eggs aggressively, and warn customers, instead of discovering 1.8 lakh spawn at the end. Comparing this season's latency and hatch figures with March's would also have shown her that temperature, not hormone, was the variable that changed.