Effect of fish feed processing conditions on digestive protease activities, free amino acid pools, feed conversion efficiency and growth in Atlantic salmon (Salmo salar L.)

Abstract

The responses of the digestive proteases trypsin and chymotrypsin and protein metabolism to differences in feed protein quality were investigated in Atlantic salmon (Salmo salar L.). Two sets of experimental feeds were produced. Each set of high and low quality feeds was provided to either 150 g or 2 kg salmon. Protein in the high quality feeds had significantly higher percentages of free (reactive) sulphydryl (SH) groups than the corresponding feeds based on low quality meals. After 90 days feeding, groups given high and low quality feeds did not differ in their specific growth rates (SGR) in either experiment. However, feed conversion efficiency (FCE) was significantly different between the high and low quality feed groups in 2 kg salmon, where the difference between the high and low feed protein qualities was larger, 10% versus 4% SH/[SH + (S-S)] in 150 g salmon. Higher FCE was preceded by significantly higher trypsin and chymotrypsin specific activities on day 60. SGR, in general, changed after the first month and was stable during the last 2 months in both experiments. Concurrently, both trypsin (T) and chymotrypsin (C) decreased with an increased activity ratio of trypsin to chymotrypsin (T/C ratio), and resulting in significantly lower T/C ratio on day 90 in salmon feeding on high quality feeds in both sizes of fish. Differences in FCE were associated with significant differences in levels of total free amino acids (TFAA) in the plasma and the white muscle, as well as in the ratio of essential to non-essential free amino acids (EAA/NEAA ratio), free hydroxyproline, and RNA in the white muscle. Interestingly, after 3 days starvation (day 93), 5-7 h postprandial EAA/NEAA ratio in the plasma was significantly lower in the high quality diet groups in both experiments. Trypsin specific activity inversely correlated with muscle TFAA levels in 2 kg salmon, concurrent with higher muscle levels of RNA, lower free hydroxyproline and higher FCE in fish fed higher quality diets. KEY WORDS

Different Dietary Levels of Protein to Lipid Ratio Affected Digestive Efficiency, Skeletal Growth, and Muscle Protein in Rainbow Trout Families

“…Deformities in juvenile tench (Tinca tinca L.) with significantly elevated whole body lipid have been reported [36]. Increased growth in Atlantic salmon (Salmo salar L.) stimulated by continuous light, which is not caused by increased protein deposition [10] but by increased lipid deposition [13], results in reduced mechanical strength and growth of the vertebrae in Atlantic salmon postsmolts [37]. Thus, stimulating fish growth without concerning with appropriate dietary P/L ratio and P/L ratio deposition in muscle or body may affect the strength of skeletal growth and cause deformities.…”

“…The inverse relationship observed between FE and white muscle protein concentration (not with body protein concentration) was probably due to a limited capacity to deposit muscle protein. Differences in FE have been associated with variations in the levels of total free amino acids in the plasma and white muscle as well as in the ratio of essential to nonessential free amino acids, and with variations in free hydroxyproline and RNA concentrations in the white muscle [18]. In addition, relationships have been observed between T/C ratio in the pyloric caeca and concentration ratios of essential to nonessential free amino acids in plasma and white muscle as well as between T/C ratio with free hydroxyproline and RNA concentrations in the white muscle [10].…”

“…[20,[28][29][30]. The protein concentration of the standards was determined using TRIzol reagent (Life Technologies, NY, USA) to obtain complete solubilisation of protein, as described in RungruangsakTorrissen [11] modified from Sunde et al [10,18].…”

“…After centrifugation at 15 000 × g for 60 minutes at 4 • C, the supernatants were kept frozen at −80 • C until analyses. Trypsin and chymotrypsin activities were determined, using benzoyl-Larginine-p-nitroanilide as trypsin substrate and N-succinylAla-Ala-Pro-Phe-p-nitroanilide as chymotrypsin substrate, according to Rungruangsak-Torrissen [11] based on Sunde et al [10,18] and Rungruangsak-Torrissen et al [16]. The concentration of protein in the crude enzyme extract was determined by the Lowry method [31] using the BioRad DC (Detergent Compatible) Protein Assay (Bio-Rad Laboratories, Calif, USA).…”

“…The growth efficiency of several fish species has been studied through variation of dietary protein levels, and the results have shown not only the relationships between dietary protein concentration and physiological parameters of consumption, growth, and protein content in body or muscle, but also shown certain increased levels of dietary protein limited consumption and growth of the fish recently, that is, [1][2][3][4][5][6][7][8][9]. Increased growth is usually not associated with an increase in protein deposition rate, that is, [10][11][12], but rather an increase in lipid deposition rate, that is, [8,13]. Traditionally in aquaculture, dietary protein and lipid are varied throughout the life cycle to optimise the economic return.…”