The Use of Fishery Wastes in the Feeds for Farmed Fish

Abstract

he potential of the three methods of using fishery wastes in commercial feeds for farmed fish was investigated; the first of these is their use in semi-moist feeds. It was found that neither the inclusion of fishery products nor the moisture content of the diet had a significant effect upon the growth rate or dry matter conversion of rainbow trout (Salmo gairdneri). In a shelf-stability trial, propylene glycol was effective as an antimycotic but had a serious, growth-depressing effect, A financial appraisal showed that no significant reductions in the cost of trout feed were possible through the use of semi-moist diets. It is concluded that there is no commercial potential of semi-moist feeds for rainbow trout at present. The use of fishery wastes as a feeding attractant was the second method investigated. Ensiled fishery wastes were sprayed onto dry diets; no consistent improvement in intake or growth rate of rainbow trout fed such diets was apparent, and fish did not preferentially select feed from demand feeders stocked with such diets. It is concluded that there is no commercial potential at present, for the use of fishery wastes as a feeding attractant for farmed fish. The use of fishery wastes in moist diets for Atlantic salmon was also investigated, The effect of ensilage upon the nutrients in mackerel silage was studied; no adverse effects were apparent. In a large-scale field trial, the specific growth rate of salmon was 75 per cent higher when fed a diet containing frozen and ensiled mackerel than when fed a dry diet. It was estimated that the financial returns to a salmon farmer would be improved by the use of such a diet despite its higher cost. It is concluded that moist diets for salmon do have commercial potential. A model that predicts the growth rate and harvest size of salmonids is presented and used in the development of criteria to evaluate competing feeds for salmon and trout.