ARS | Publication request: MEASURING VARIATION IN FEED EFFICIENCY OF RAINBOW TROUT ON INDIVIDUAL FISH

Submitted to: Aquaculture America Conference
Publication Type: Abstract
Publication Acceptance Date: October 1, 2002
Publication Date: February 18, 2003
Citation: Silverstein, J. 2003. Measuring variation in feed efficiency of rainbow trout on individual fish. Aquaculture America Conference.p. 267.

Technical Abstract: The largest variable cost in fish production is feed. For this reason, improving feed efficiency is of major importance to aquaculturists as it has been for all animal production industries. A method that has been used successfully in terrestrial animal production industries (chickens, pigs and cattle) to identify animals with greater efficiency is measurement of residual feed intake (RFI). The underlying idea is to predict how much the average fish would need to consume to grow a given amount (predicted intake). Then the actual amount of feed consumed in growing fish is measured (observed intake). The difference between the predicted intake and observed intake is the RFI. In the current experiments rainbow trout were held individually in single 100L aquaria and fed to satiation twice daily. A bioenergetics model (Fish Bioenergetics 3.0) was used to model feed consumption based on recorded growth. The values for feed consumption based on fish size, and environmental temperature predicted by Fish Bioenergetics 3.0 were compared to the actual consumption values to yield RFI (RFI= predicted intake - observed intake*100/predicted intake). Two rounds of this protocol were conducted, the first round to investigate the acclimation and variation in RFI for rainbow trout held in individual aquaria, and the second round compared fish from different strains of rainbow trout. The first round was a 3 week trial with fish initially weighing (mean ±SEM) 51.9±0.7g and ending at 72.8±2.5g. Consumption as a percent of body weight increased from the first week of acclimation through the third week from 0.97±0.13% to 2.34±0.12%. The first week the mean RFI was overall negative and highly variable -66.8±59.4% as fish began to feed and grow slowly. The RFI rose to -21.0±6.6% by the third week when fish adjusted to their surroundings and RFI variability was reduced. Generally, the fish ate more than the model predicted they would eat. In the second trial fish initially weighed 17.05±0.78g and grew to 35.08±3.44g over 4 weeks. Consumption differed significantly between the two strains (1.22±0.14 vs. 0.77±0.20%) over the first week of the trial, but the difference declined each week. The RFI was positive in this trial, most fish ate less than predicted by the model. In the acclimation period RFI was 56.50±2.24% and dropped to ~ 35 to 38% over the following 3 weeks. There were differences between the strains for consumption and growth, however the differences were not due to any difference in RFI, a corollary for efficiency. Consumption and growth were highly correlated (R2>0.95), but there was no significant relationship between consumption and RFI.