Induced Spawning Techniques

Spawning techniques used for river coarse fish are based on the classic carp hypophysation method originally developed in Hungary. The technique is to inject the brood fish with a pituitary extract or synthetic hormone preparation when the fish is "ripe" and ready for spawning. This mimics the natural hormone surge, which happens in the fish at this time. The hormone is administered as a single dose or split up into two separate doses called the "primer" and "resolver", with the injections usually being 12-24 hours apart.

The males and females are held in separate cages in warm water broodfish holding tanks and depending on the species, ovulation takes place between 12 and 24 hours after the resolving dose has been given.

The adults are "dry" stripped when ready and the eggs treated with a solution containing 4g of sodium chloride and 3g urea in 1 litre of distilled water. This helps to extend the motility of the spermatozoa and improves the fertilisation rate of the eggs. After 10-30 minutes the eggs are gently poured as a single layer onto 1.5-2.5mm fine mesh stainless steel trays placed inside G.R.P. troughs. Each trough is supplied with 2.5 to 5 litres/min of water via longitudinally mounted spray bars. The eggs (with the exception of barbel, which are non-sticky), adhere to the trays and are incubated for between 7 and 30 days depending upon on species and incubation temperature.

When the larvae swim up for the first time there is a small amount of yolk reserve left. Before all of this "internal" food has been used up, the larvae must be fed or stocked out. The period of mixed endogenous (internal), and exogenous (external) feeding only lasts for 2 or 3 days and the larvae must be supplied with an abundance of food otherwise the majority will die or suffer irreversible damage. Natural food such as rotifers and protozoans or we use artificial diets such as larvae feed, microencapsulated egg yolk preparations or artemia shrimp.