Digestive tract morphology and enzyme activities of juvenile diploid and triploid Atlantic salmon (Salmo salar) fed fishmeal-based diets with or without fish protein hydrolysates

Abstract

Triploid, sterile Atlantic salmon (Salmo salar) could make a contribution to the development of the farming industry, but uncertainties about the performance and welfare of triploids have limited their adoption by farmers. In this study, we compared the ontogeny of digestive tract morphology and enzyme activities (pepsin, trypsin, chymotrypsin, alkaline phosphatase and aminopeptidase) of diploid and triploid Atlantic salmon. Fish were fed diets based on fishmeal (STD) or a mix of fishmeal and hydrolysed fish proteins (HFM) whilst being reared at low temperature from start-feeding to completion of the parr-smolt transformation. Fish weights for each ploidy and feed combination were used to calculate thermal growth coefficients (TGCs) that spanned this developmental period, and the data were used to examine possible relationships between enzyme activities and growth. At the end of the experiment, faeces were collected and analyzed to determine the apparent digestibility coefficients (ADCs) of the dietary amino acids (AAs). Digestive tract histo-morphology did not differ substantially between ploidies and generally reflected organ maturation and functionality. There were no consistent differences in proteolytic enzyme activities resulting from the inclusion of HFM in the diet, nor was there improved digestibility and AA bioavailability of the HFM feed in either diploid or triploid fish. The triploid salmon had lower ADCs than diploids for most essential and non-essential AAs in both diets (STD and HFM), but without there being any indication of lower intestinal protease activity in triploid fish. When trypsin-to-chymotrypsin activity and trypsin and alkaline phosphatase (ALP) ratios (T:C and T:ALP, respectively) were considered in combination with growth data (TGC) low T:C and T:ALP values coincided with times of reduced fish growth, and vice versa, suggesting that T:C and T:ALP may be used to predict recent growth history and possible growth potential.

Estimation of Phosphorus and Nitrogen Waste in Rainbow Trout (Oncorhynchus mykiss, Walbaum, 1792) Diets Including Different Inorganic Phosphorus Sources

“…On the other hand, plant protein registered lower capacity than fish meal and gluten [46]. Thus, the ingredients used in diets can modify feed BC, as has been reported in sea bass (Dicentrarchus labrax) [47], Atlantic salmon (Salmo salar) [48] and sea bream (Sparus aurata) [49,50]. In the current experiment, the buffering capacity of SCP-2% was significantly lower (866 meq HCl/kg) than the rest of the inorganic phosphates (1966 meq HCl/kg), which might imply an advantage of including this additive in fish diets, as has been reported [51].…”

Zootechnical Parameters and Enzyme Activity in the Species Brycon moorei (Steindachner 1878)

“…In the present study, no trends between variations in serum enzyme activity and protein inclusion levels were found in this regard; the contribution of each enzyme to protein hydrolysis in the fish intestine is still unclear and subject to debate [59,77]. However, with respect to the T:C ratio, a strong tendency to decrease was observed relative to the feeding protocol, specifically when switching from FL to A; it has been determined for other species that, when this ratio drops, it coincides with low growth rates [78,79].…”

Addressing Phosphorus Waste in Open Flow Freshwater Fish Farms: Challenges and Solutions

“…The changes in phosphorus requirements resulting from temperature, fish size, and life stage highlight the importance of considering the growth trajectory and physiological status of fish when formulating diets and managing phosphorus levels in their aquaculture systems. For example, body size affects the physiological processes and energy metabolism, and triploid fish may exhibit higher phosphorus requirements [104]; larvae and juvenile fish exhibit significant phosphorus requirements due to their rapid growth and increased tissue turnover [39]; larger fish have greater skeletal mass and overall body size, which necessitates the dietary absorption of phosphorus [6], whereas at older stages, gonadal development can also result in increased phosphorus requirements [105]. The above parameters can also interact with temperature, with low temperatures resulting in poor nutrient absorption and lower retention of dietary phosphorus, and high temperatures causing increased metabolic rates and nutrient requirements, potentially leading to increased feed intake and pollution [106].…”