TROUT are troublesome for fish farmers because harvesting their eggs is laborious and expensive. So a team of European researchers has developed a hormone-laced food that makes the fish spawn predictably.
Trout commonly spawn over a two-month period, during which they must be inspected regularly to decide whether their eggs are ripe and can be manually harvested. But because farms can stock thousands of fish, the inspection process is laborious.
Now, however, researchers believe they can get around the problem by feeding trout microspheres laced with gonadotrophin-releasing hormone (GnRH), which encourages the fish to produce eggs. The hormone is combined with a chemical that increases the permeability of the intestine wall, allowing enough of the hormone to be absorbed to be effective. 鈥淲e use cellulose to make the microspheres and incorporate the hormone and absorption enhancer into the matrix,鈥� says Olivier Lescroart of the Catholic University of Leuven in Belgium.
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Lescroart and his colleagues at Intervet International in Boxmeer, the Netherlands, added the microspheres, which are half a millimetre across, to fish food pellets. They proved very effective when tested on trout in the laboratory: the eggs were typically ready to be harvested within eight days, says Lescroart. The same technique could also be used in salmon farming, according to the researchers.
Fish fed the hormone will not end up on supermarket shelves. The feed is given only to brood stock, those fish used exclusively for egg production.
But some scientists remain unconvinced. 鈥淭here is some advantage in synchronising when fish spawn, but it鈥檚 doubtful whether the commercial need is strong enough,鈥� says Niall Bromage of the Institute of Aquaculture at the University of Stirling. There could be other problems, too. 鈥淏y inducing spawning you run the risk of getting poor quality eggs鈥攖he fish may ovulate, but the eggs could be infertile,鈥� Bromage says.
Another hurdle the European team has to overcome is acceptability鈥攅specially with salmon farmers. According to Tony Hawkins of the Scottish Executive鈥檚 Fisheries Research Laboratory, salmon farmers oppose the use of hormones as they smack of intensive farming techniques and could damage the industry鈥檚 public image. 鈥淭he industry would run screaming in the other direction,鈥� he says.