High growth rates in Atlantic salmon (Salmo salar L.) fed 7.5% fish meal in the diet. Micro-, ultra- and nano-filtration of stickwater and effects of different fractions and compounds on pellet quality and fish performance.

Abstract

The intention of this study is to investigate the effect of fish meal soluble protein quality on growth and protein utilisation of Atlantic salmon fed very low fish meal diets. For this purpose stickwater (SW) was separated during herring meal production, fractionated following successive micro- ultra- and nano-filtration steps and reintroduced in the press cake (PC) in order to produce 4 reconstituted fish meals containing different molecular size soluble protein mixes. The SW fractions used for the production of the experimental fish meals were: 1) the micro-filtration (MF) retentate, 2) the ultra-filtration (UF) retentate, 3) the nano-filtration (NF) retentate and 4) the nano-filtration permeate. Four very low fish meal experimental diets were prepared containing 25gkg−1 super prime fish meal and 50gkg−1 diet of one of the 4 experimental fish meals produced. A positive control diet was prepared containing 300gkg−1 diet super prime fish meal. Three more diets were prepared containing 25gkg−1 diet super prime fish meal and 50gkg−1 diet PC. Two of them were supplemented with either crystalline taurine, or crystalline hydroxyproline, up to the levels present in the high fish meal control diet. The experimental diets with the SW fractions contained similar levels of water soluble protein (WSP), which were higher than in the PC diets and lower than in the control. All diets were iso-nitrogenous, iso-lipidic and iso-energetic and were fed to 8 triplicate groups of salmon (80 fish per group of initial body weight 133g), for 69days. High growth rates and low fish in-fish out ratios (FIFO) were achieved in salmon fed all the very low fish meal diets. Feed intake, fish body growth, whole body protein content, protein gain and morphometry were significantly affected by the inclusion of the different SW fractions in the low fish meal diets. The medium size peptides (UF retentate) induced significant increase in feed consumption in salmon and supported higher fish growth compared to the highest (MF retentate) or the lowest molecular weight peptides (NF permeate) where both feed intake and fish growth were reduced. The fish fed the diet containing the NF permeate had significantly lower growth compared to the diets containing the other SW fractions. We did not find any benefits for salmon performance by the supplementation of taurine or hydroxyproline alone to the low WSP PC diets. The present work gives evidence on the multi-dimensional effects of the different marine water soluble components on fish performance. In order to identify novel, high added-value, water soluble marine compounds, advanced large scale separation technologies must be further developed and applied in studies investigating specific functional effects that these compounds may have on fish and other organisms.