Hatching fish eggs out of water A novel incubation technique developed in CE could pave the way to new thinking in hatcheries

The new fish hatchery is a compact cabinet but can incubate a million carp eggs.

Experiments by a young geneticist, on white mice oocytes in an embryological laboratory, have led to the development of a new form of fish egg incubator, from biochemical laboratory company. As a routine procedure, he kept fertilized mouse ova in silicone oil, where they developed perfectly. Later, he also stored fish eggs in silicone, and these also developed well.

This observation, combined with the knowledge that pike-perch eggs can be incubated out of water in a damp spray, motivated a series of experiments. A small group of researchers- the geneticist, an electrical engineer and a fish biologist- began investigating a practical means of fish egg incubation and hatching out of water.

Their criteria were that: the new method should involve low water and energy consumption; survival should be at least equivalent to that provided by traditional incubators; sterilization should not involve malachite green, antibiotics or other banned chemicals; labor should be minimal; hatching should be at an optimal time, and the incubator should work both for freshwater and seawater fish eggs - preferably for most cultured species.

The first experiments used common carp eggs, and established that incubation did not require water, iust moisturized air.

The fertilized eggs were placed on net with a mesh of about 2/3 of the eggs' diameter. Metal or plastic nets made of filamentous material proved unsuitable; hard nets were best.

To increase capacity, the optimum number of eggs to be placed on the net-tray was established. In the case of carp, good results were achieved with up to 2-3 layers of eggs.

Sometimes, usually in batches with low fertilization rates, infections led to mass mortality. This was mostly when moisture was over 100 per cent in air, and the water condensed in droplets on the eggs.

With relative humidity lower than 99 per cent the eggs were damaged through drying out, which meant precise temperature- humidity regulation was needed. After a year of experimentation, this was successfully refined.

The problem of sudden infections causing high egg losses remained. A further year was spent testing several chemicals and treatments to reduce the losses.

A tannic acid solution was the answer, and once the treatment was perfected, even batches of eggs with less than l0 per cent fertilization rate were free of external fungal or bacterial infections without using malachite green or antibiotics.

The next step was to test the method for pelagic fish eggs, such as white amur or bighead carp. Even these fine and sensitive eggs can be hatched in „air”. The machine was also tested for tench, koi, amur, bighead, wels, African catfish and sterlet.

Later versions of the incubator have an automatic feature for separating the egg shells and larvae after hatching.

The latest, and best, variant is made from material resistant to sea water corrosion. It is programmable for different species, and has even been tested for hatching the eggs of Atlantic cod. Survival was no lower than that of the control group. Technically the new fish hatchery measures 1115 x 1900 x 890mm (HxWxD), and uses 400 l of water per 60 hours for the incubation of 1,000,000 carp eggs.

Before marketing, the machine needs to be tested for other sea-water fish as well as salmonids, but since CE has no sea, this is not easy, and the company are now seeking a foundation or partner to complete the job.

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