Abstract

The purpose of this study was to examine the effects of Rare Earth Elements (REE) on growth performance and meat quality parameters of fresh water fish. The general setting for this nutritional experiment is based on data from China, where remarkable effects have been achieved using REE as growth promotors for almost all agriculturally utilizable species as well as for fish-farming. The goal was to examine whether we could reproduce the results of the Chinese experiments under western livestock husbandry conditions. Since in pig production, our data give highest effects with REE-citrate, this compound was also chosen for the fish studies. Therefore a feeding experiment was conducted with carps (Cyprinus carpio L.) and rainbow trouts (Oncorhynchus mykiss), known as the most common species in the production of fresh-water fish. For the first experiment a REE-citrate mixture was homogenously mixed into a trout diet at a concentration of 0ppm, 100ppm, 200ppm and 400ppm. The rainbow trouts had an average initial weight of 145g and were divided into four groups of 200 fish each. For 12 weeks the parameters weight gain, feed-intake and feed-conversion ratio were determined. At the end of the experiment the weight of fish fillet, pH-Value, meat colour und fish meat texture were analysed. No positive effects of the REE on growth performance and feed-conversion ratio could be observed. The meat quality of the REE-groups did not differ from that of the control group. In the carp experiment 3050 animals with an average initial weight of 30g were distributed to eight natural ponds. The control group (4 ponds) obtained a customary pellet diet for carp; the experimental group (4 ponds) obtained the diet supplemented with REE–citrate to maintain a concentration of 400ppm. Over a period of 14 weeks the development of weight gain, the feed-intake and the feed-conversion ratio were documented as performance parameters. After the experiment the changes in the content of fat and protein in fish were examined. Although several ponds displayed positive tendencies, the total result was that the supplement of REE does not influence body weight gain rate or feed-conversion ratio in a positive way. These results indicate that REE, supplemented to fish, does not improve any performance parameters of fish, contrary to other farm animals.