R Hauler

Fish meal replacement by plant meals in extruded feeds for Atlantic salmon, Salmo salar L.

The replacement of fish meal protein with soybean meal (SB) or protein concentrates made from narrow-leafed lupin (LP) or field peas (PP) was investigated in extruded feeds for Atlantic salmon. Salmon (47 g) were fed for 63 days on extruded feeds containing each of the plant meals to replace 25% and 33% of the fish meal protein and performance compared against a nutritionally balanced control and a commercial salmon feed formulation (extruded under the same conditions). There were no significant differences in weight gain between the control and feeds containing the plant proteins. The commercial feed produced significantly higher weight gain than the control feed and LP at both replacement levels. Feed consumption was significantly higher for LP at 33%, but there were no other significant differences between the other feeds. Feed efficiency ratio (FER) and productive protein value (PPV) were highest for PP and SB and not affected by inclusion level, whereas they were significantly lower for LP at 33% inclusion. The weight gain and feed efficiency ratio data showed that soybean meal and pea protein concentrate had the best potential for replacing at least 33% of the fish meal protein in extruded salmon feeds and that lupin protein concentrate was less well utilised at the higher inclusion level. These results support the use of processed plant meals as important replacement protein sources for fish meal in extruded feeds for Atlantic salmon.

Reevaluation of the Quantitative Dietary Lysine Requirements of Fish

Studies on the quantitative lysine requirements of fish are numerous and have employed a range of methods. In this review, dose-response dietary lysine requirements are shown to have considerable intraspecies variation that cannot be explained by the particular laboratory variables between experiments (dietary formulation, fish growth rate, statistical model, and response criteria). Alternatively, it is demonstrated that marginal lysine intake in dose-response experiments is utilized for liveweight gain (LG) with an equivalent efficiency (54.1 mg LG.mg−1 lysine intake). Equivalent lysine utilization for LG means the lysine requirements of fish are not dissimilar when expressed relative to LG — and estimated to be 18.5 g lysine.kg−1 LG. Expressed relative to LG, lysine requirements of rainbow trout range between 15.7 and 21.1 g lysine.kg−1 LG, which represents an order of difference of only 34%. Due to a constant lysine requirement for LG, dietary lysine concentration is determined by feed efficiency ratio (kg LG.kg−1 feed intake). Consequently, increased feed efficiency with increased dietary energy results in a constant requirement expressed as lysine to energy ratio. It is recommended that future amino acid requirements of fish be expressed relative to gain (LG or protein) to improve current variation between studies.