How to Prepare Carp Pituitary Extract for Injection

What you need on the bench

• A scale reading to 0.01 g. A 1 mg error on a 2 kg fish is a 15% dose error. Kitchen scales are not good enough.
• A glass homogeniser, or a dry mortar and pestle. The gland must be ground to a smooth paste or fine powder — coarse grit injects badly and releases little.
• Chilled saline, 0.65–0.9% sodium chloride. Fish plasma is closer to 0.65%; 0.9% is what most hatcheries have on the shelf and works fine.
• 1 ml insulin syringes with fixed needles. You will be injecting fractions of a millilitre, and a 5 ml syringe cannot measure that.
• An ice pack or a cool box. The suspension degrades faster warm.

The five steps

1. Weigh what the batch needsAdd up female body weight, multiply by your dose per kg, and weigh that much dried gland. For 200 kg of females at 3 mg/kg that is 600 mg — a little over half a vial.
2. Grind to a fine powderGrind in short bursts, scraping the sides down. Stop when you cannot feel grit between your fingers. This is the step people rush, and it is the one that costs the most potency.
3. Suspend in chilled salineAdd saline at the ratio in the table below and mix thoroughly. The suspension will be cloudy grey-white; that is correct.
4. Separate the solidsCentrifuge at 3000–5000 rpm for 10–15 minutes. No centrifuge? Let it stand 10 minutes and draw the cloudy layer from just under the surface with a syringe, leaving the sediment behind.
5. Inject the same dayDraw into 1 ml syringes, keep them shaded and cool, and use them within a few hours. Discard whatever is left at the end of the run.

Choosing a working concentration

This is where most first-time batches go wrong. Mix too strong and the injection volume becomes too small to measure accurately; mix too weak and you are injecting millilitres of fluid into a fish that weighs two kilograms.

A 0.75 ml injection is comfortable to measure and gentle on a 2.5 kg fish. A 0.075 ml injection needs a 1 ml syringe and a steady hand, and a small error there is a large error in dose.

How long a mixed suspension stays usable

Signs the batch has gone wrong

• The suspension smells sour or ammoniacal. Bacterial growth. Discard it — injecting it will do more harm than skipping the spawn.
• It will not stay cloudy and settles into clear liquid plus hard sediment within a minute. Usually under-grinding, or the powder took up moisture in storage.
• Nothing happens at the expected hour. Before blaming the gland, check water temperature and whether the priming dose was actually given. Temperature error explains most "dead batch" stories.

Extract, or grind and inject whole?

Some hatcheries skip the separation step and inject the whole ground suspension, sediment included. It works, and it saves a centrifuge, but the solids block fine needles and the dose becomes uneven between syringes. If you are injecting more than a few dozen fish, take the extra ten minutes to separate the supernatant.

Commercial liquid extracts exist too. They are convenient, but they are also diluted, shorter-lived and priced per millilitre rather than per gram of gland. For a hatchery running its own spawning nights, dried gland plus saline is the cheaper route — and the one where you know exactly how much gland went in.