Preparation and evaluation of diets containing fish silage, cooked fish preserved with formic acid and low-temperature-dried fish meal as protein sources for mirror carp ( Cyprinus carpio)

Abstract

Fish silage, cooked fish preserved with formic acid and low-temperature-dried fish meal were prepared from whole whiting ( Merlangius merlangus) and incorporated into diets suitable for feeding to mirror carp fingerlings ( Cyprinus carpio). The diets contained 33% crude protein on a dry matter basis of which one third was derived from the experimental fish preparations. The diet containing fish silage exhibited poor water stability and rapid leaching of the soluble nitrogen fraction. Intake of the fish silage diet was slow compared with diets containing cooked fish and fish meal whilst mortality reached 40% in one replicate. A significant difference in specific growth rates was noted between carp fed the fish silage diet and those fed the cooked fish or low-temperature-dried fish meal ( P = 0.05) i.e. 1.25, 1.70 and 1.64 respectively. Mean feed conversion ratios (g dry feed/g liveweight gain) were 1.86, 1.31 and 1.36 respectively. Poor diet palatability and loss of nitrogen by leaching appeared to be limiting factors to the growth of carp fed the fish silage diet. The preservation of waste fish for inclusion into fish feeds by the acid treatment of cooked fish appears to merit serious consideration as an alternative to preservation by drying.