Induced Breeding of Carp with Pituitary Gland

Why the injection is needed at all

In the wild, carp spawn when the environment tells them to: water levels rise, rain falls, temperature climbs and current picks up. In a hatchery pond none of that happens reliably, and a female that is physiologically ready will simply hold her eggs and reabsorb them.

Pituitary gland material carries the gonadotropins that would normally be released at that moment. Injecting it replaces the environmental trigger with a chemical one, so the whole run — injection, ovulation, stripping, incubation — can be scheduled rather than waited for.

Step 1: Choose fish that can actually respond

The most common reason a spawn fails is not the dose, the gland or the timing. It is a female that was never going to ovulate because she was not ripe. Check before you inject, not after.

For males the test is simpler: press lightly just behind the pelvic fins. Free-flowing milt means ready. A male that produces only a thin smear will waste a female.

Step 2: Prepare the fish and the water

• Hold broodstock separately. Females and males in different tanks, so you control the meeting rather than discovering it happened overnight.
• 24 hours in clean flowing water. This settles handling stress and clears the gut.
• Temperature is the schedule. Below 18 °C the response is unpredictable; 22–27 °C is the working window. A five-degree change between injection and ovulation moves your harvest by hours.
• Keep handling to a minimum. A fish chased around a tank for ten minutes before injection may not respond at all. Net, weigh, inject, release.

Step 3: Inject

Dose depends on species and body weight — the dosage chart covers the working ranges. The mechanics matter just as much:

• Weigh every fish individually, or at least weigh each tank batch. Guessing by length is where underdosing starts.
• Inject into the muscle at the base of the dorsal fin, or into the pectoral fin base. Both are safe and easy on a wet, moving fish.
• Insert the needle at a shallow angle, about 5–10 mm deep for a 2–3 kg fish. Too deep risks the body cavity; too shallow leaks.
• Record the time. The second injection is scheduled from this moment, not from when you finish the tank.

The first injection is 10–15% of the total dose; the second, 6–12 hours later depending on temperature, is the remaining 85–90%. Males receive their single dose alongside the second female injection.

Step 4: Wait, and then check instead of guessing

Ovulation follows the resolving injection by roughly 9–12 hours at 24–26 °C, and 12–16 hours at 20–22 °C. Start checking from hour 8.

To check, lift the fish gently, hold it head-up over a dry bowl, and press the abdomen from front to back with a flat hand. If eggs flow in a stream, strip now. If a few eggs appear, check again in 30–45 minutes. If nothing comes and the abdomen is still firm at hour 16, the run has failed — return the fish to the pond rather than injecting again the same night.

Step 5: Strip and fertilise

1. Dry the fish and the bowlWipe the abdomen and use a dry bowl. Water activates sperm prematurely and kills it before it reaches an egg.
2. Strip the eggsGentle pressure from front to back, working towards the vent. Collect into the dry bowl. Never squeeze hard — ruptured tissue ruins the batch.
3. Add miltStrip two males over the eggs, or add collected milt. One male per two females is the usual ratio.
4. Mix, then add waterStir gently with a feather or your hand for 30–60 seconds, then add clean water to activate the sperm. Mix for another minute.
5. Rinse and move to incubatorsRinse off excess milt and blood with clean water, then transfer the eggs to hatching jars or trays. Eggs swell and become adhesive within minutes.

Step 6: Incubate

Keep water moving over the eggs and remove dead white eggs as soon as you see them — one dead egg can fungus and take a cluster with it. Hatch rates of 60–80% of fertilised eggs are normal; anything below 40% points to a fertilisation problem rather than an incubation one.

When nothing happens: the checklist

Work down this list in order. It is sorted by how often each cause is the real one.