Digestive efficiency, free amino acid pools and quality of growth performance in Atlantic salmon (Salmo salar L.) affected by light regimes and vaccine types

Abstract

This study comprised the results of three different seawater trials using unique combination of techniques to study protease digestive efficiency and growth performance quality to illustrate the effects of light regimes and vaccine types in Atlantic salmon (Salmo salar L.). Fish with higher growth had higher trypsin (T) and chymotrypsin (C) specific activities with higher T/C ratio or slope T/C ratio [calculated from the regression between trypsin (y) and chymotrypsin (x) specific activities] in the pyloric caeca. The T/C ratios indicated fish growth rates over a period of 1-2 months, while the slope T/C ratios indicated fish growth rates at sampling. Adaptation period for adjustment to the new environment of continuous light was 70 days, indicated by the differences in trypsin specific activities and the crossing of slope T/C ratio regressions following with the changes in growth rate directions between the control and the treated group. Vaccine types affected fish vertebral growth, and additional continuous light enhanced the impact of vaccines on fish growth during springtime, indicated by differences in slope T/C ratios. Continuous light stimulated fish growth during winter to spring, when the natural day length was short, without significantly changing white muscle and oocyte qualities in the fish of about 500 g, except for significantly increased white muscle RNA concentration. Continuous light also reduced fish growth rate later during summer, when the natural day length was long, by precedently decreasing the T/C ratio in late spring. Interestingly, plasma levels of free lysine related to tryptic digestion were correlated with trypsin specific activity levels. Continuous light caused higher levels of most free amino acids (FAA) involved in nitrogen metabolism, higher incorporation of essential FAA for protein synthesis, and higher protein turnover rate (free hydroxyproline levels) in both plasma and white muscle. However, continuous light did not affect higher protein content, intracellular buffering capacity and RNA levels in the white muscle of the fish of about 1 kg, probably due to limitation of FAA available for protein synthesis. It is therefore suggested that enhancing fish growth by continuous light stimulation should be accompanied by increasing availability or content of dietary protein (and probably minerals), which in turn would improve the quality of fish growth performance through increasing fillet protein concentration, strengthening vertebral growth, and delaying oocyte development.

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

“…A reduction in T/C ratio in the HP-diet fish, relative to NP-diet fish, caused by a greater increase in the activity of chymotrypsin over trypsin confirmed a reduction in growth rate (Table 2). This has been reported in several works [11,12,14,18,32]. The confirmation is also strengthened by the observed associations between trypsin specific activity and high growth and between chymotrypsin specific activity and low growth (Table 4).…”

“…Thus, the T/C ratio has an effect on growth efficiency independent of the specific activity level of the proteases. This has also been observed in Atlantic salmon [32] and gene manipulated fish [10,41]. A reduction in T/C ratio in the HP-diet fish, relative to NP-diet fish, caused by a greater increase in the activity of chymotrypsin over trypsin confirmed a reduction in growth rate (Table 2).…”

“…The in vitro protein digestibility of diets has been affected by genetic differences in trypsin phenotypes [33,38], and different trypsin phenotypes affected variations in the protease activity expression levels [14] and FE [42]. At sampling in November 2003, the fish were at a similar steady growth phase showing by similar slope T/C ratio ( Figure 3) (details in [32]) and no correlation between trypsin specific activity and the T/C ratio (data not shown) (details in [12,14]). At steady growth phase, utilization of protein for deposition and growth would be reduced to a maintenance level that should be steady irrespective of diet.…”

“…Growth status of the fish is very important for interpreting biological parameters. At present, the slope T/C ratio and the relationship between trypsin specific activity and the T/C ratio in the pyloric caeca seem to be the only indicators available for predicting relative growth level and growth status of the fish at sampling, respectively, without knowing fish history see [12,14,32]. Our results suggest the association between the diet dependent in vitro protein digestibility value and protein growth in fish, whereas the T/C ratio is associated with fish growth regardless of protein or lipid growth.…”

“…The enzyme specific activities were expressed as μmol p-nitroaniline produced h −1 mg protein −1 . The protease activity ratio of trypsin to chymotrypsin (T/C ratio) was directly calculated from each individual, and the slope T/C ratio was obtained from the regression between trypsin (y-axis) and chymotrypsin (x-axis) specific activities at each sampling period [32].…”