Bioactive peptides boost fish farming
French, Dutch and Belgian researchers have developed a simple yet effective way of controlling the reproduction of farmed fish using an orally delivered bioactive peptide. Background To maximise the number of fish that are hatched, fish farmers strip pregnant fish of their eggs and place them in hatcheries. However, many commercially valuable fish, such as trout, spawn over a relatively long period of time, typically up to two months. This means that the farmer must visually inspect each breeding fish at least once a week. Spawning can be induced by injecting the fish with a peptide gonadotrophin-releasing hormone (GnRH), but this is labour intensive, and stressful for the fish. Now, researchers have found a way to introduce this peptide via fish food. Description, impact and results The work was carried out in two phases. Under the EU's Fisheries and Aquaculture Research (FAR) programme, the researchers first developed the basic oral delivery method. The method comprises microcapsules approximately 500 microns in size that contain both the peptide hormone and an absorption enhancer. The enhancer was designed to improve the peptide's uptake in the intestine of the fish by increasing the permeability of the intestine wall. The next phase was to produce a commercial product - this was carried out under the EU's Innovation programme. To achieve this the researchers had to incorporate the microcapsules into food pellets with a diameter of roughly 0.5 cm, while overcoming the problem that these capsules were highly sensitive to heat and moisture. They achieved this by employing the appropriate binders, but then hit a second hurdle. Fish food passes through the stomach very slowly, so the level of peptide released into the blood stream was insufficient to induce spawning. To overcome this problem, the researchers had to completely reformulate the product. The pellets have now been used successfully with catfish, but the main interest lies in trout farming. Laboratory trials with trout have worked well, and a large-scale testing programme on a commercial trout farm is planned. In the longer term, the peptides are expected to be adopted in the salmon industry, which is of particular economic importance in Ireland, the United Kingdom and Norway. With many of Europe's fish stocks now heavily depleted, the new hormone-containing pellets could contribute significantly to providing EU consumers with a plentiful supply of fresh fish at an attractive price. Working partnerships The project was led by the Laboratory of Aquatic Ecology at the Catholic University of Leuven in Belgium. The Netherlands-based animal health company, Intervet International supplied the peptide and the absorption enhancer. Two French partners were also closely involved: the laboratory trials on trout were carried out at the fish physiology laboratory, INRA, in Rennes, and the large-scale trials are currently being undertaken at a fish farm which is part of the fish and poultry farmers' co-operative, SYSAAF.