Environment Agency scientists at its Fish Farm in Calverton, Nottingham, have recently completed a ‘first’ in the world of fish rearing. They have bred a young Twaite Shad, a fish native to the British Isles which has never been spawned and bred in captivity before.
The young fish will be monitored, providing an insight on the breed and this information will be used to produce a ‘key’ which will allow future identification of Twaite Shad larvae. This advance means future, fisheries scientists could rear large numbers of the fish if required.
Like the Salmon, Twaite Shad spend most of their lives at sea and only return to fresh water to spawn. In May and June, when the adults are four or five years old, they congregate in shoals and swim up into the rivers, looking for fast gravel runs on which they spawn. Agency fisheries staff from Welsh and Midlands regions worked together to collect brood Twaite Shad from the rivers Usk, Teme and Wye, transporting them to Calverton. Special facilities had to be designed and built at the farm because the Shad is extremely delicate.
Fish Farm Team Leader, Mr Alan Henshaw, says: ‘Very little is known about the reproduction of the Shad so we didn’t have much information to work with. However, the data we have recorded during the process will be used in the future. As part of the breeding programme, we used techniques developed by colleagues in the US to spawn the American Shad, a larger cousin to our native species.’
This was done by injecting a small pellet into the fish which slowly releases a hormone and initiates the reproductive process. In the wild, fertilised eggs lodge between spaces in the gravel of the river bed, but at Calverton, eggs were collected in fine mesh socks placed over the holding tank outlets.
The tiny, clear eggs take four to five days to hatch. After about a week, the larvae will hatch and are fed small brine shrimp. Calverton staff are currently rearing the young ‘fry’, which are growing quickly, in circular tanks.
The Agency’s fish farm at Calverton carries out important fisheries research for the whole of England and Wales. It investigates issues, such as the effect of pollution on fish stocks, and also works to preserve and improve fish stocks throughout the country.
