Effects of progressive decrease of feeding frequency and re-feeding on production parameters, stomach capacity and muscle nutritional value in rainbow trout (Oncorhynchus mykiss)

Feeds and feeding constitute the major part of costs in intensive aquaculture. Any action to reduce feeding costs without negatively affecting fish production parameters and flesh quality would improve profitability of farming. Therefore, we studied the effects of feeding frequency on production parameters, stomach capacity and nutritional value of muscle in juvenile rainbow trout (Oncorhynchus mykiss) in an experiment with two stages. First, during the nine-week starvation period we fed rainbow trout (initial weight c. 40 g) with four different feeding protocols in an attempt to adapt the fish to a progressive decrease in the number of feeding days. During the second stage, a four-week re-feeding period, all fish were fed in excess on weekdays. Fish growth, feed intake, stomach size, and biomolecule content of muscle were monitored as response variables. During the starvation period, feed intake and growth decreased along with the number of feeding days. Compensatory growth during the refeeding was either only modest or absent. The fish in the starved groups were unable to significantly increase their stomach capacities. Starvation and re-feeding had only a slight effect on muscle fatty acid and amino acid composition. The used feeding protocols did not affect important production parameters (e.g. feed conversion or size variation). Our results suggest that despite differences in fish growth starvation and re-feeding hardly affect the nutritional value of fish. It is possible that several decades in captivity have made rainbow trout incapable to adjust their stomach size in respect to feeding frequency.