The Effect of Non-Steroid Growth Promotants on the Growth of Common Carp

Abstract

Feed additives are widely used in livestock production to improve animal performance. These additives include antibacterial agents (ABA), steroid hormones, minerals and vitamins. Low concentrations of antibiotics are commonly added to livestock feedstuffs in order to stimulate body growth. In fish antibiotics have not been used and even when they were applied experimentally in the past they did not seem to improve growth rate. However in the present study, for the first time, some ABAs such as virginiamycin, terramycin and payzone have been shown to increase the weight and feed conversion efficiency of the fish significantly and to a lesser extent so have other antibiotics such as tylosin and avoparcin. These feed additives were tested mainly on mirror carp Cyprinus carpio. The mode of action of these antibiotics on growth were sought. This investigation included their effect on the bacterial population of the intestinal tract, on the histology of the gut and on their possible protein sparing effect. In order to study possible protein sparing ABA were added to diets containing two levels of protein ( low: 25%and high: 38%). Other substances such as zeranol, a weak hormone-like compound, and emtryl a protozöcide were also examined for their effects on growth and were compared with the effects of ABA. The role of all these feed additives on the biochemical composition of the muscle of the fish and on their liver, kidney and intestine were also investigated. The results showed that ABA that promoted growth significantly tended to increase the fat content of fish. Unlike ABA zeranol increased the protein and water content of the muscles of the treated fish. Two antibiotics virginiamycin and terramycin, were injected into carp subcutaneously to ascertain their effect by different routes of administration. The effect was negative which may give support to the hypothesis that antibiotics act on the bacterial flora of the intestine to promote growth. Finally the safety of the use of these feed additives and their residues in the edible tissues were discussed. The general conclusion of the study is that ABA can promote growth offish but that there is no clear evidence that they promote this growth through effect as bacteriocidal agents.