Effects of graded levels of medium chain triglycerides and cysteine on growth, digestive processes and nutrient utilization in sea water reared Atlantic salmon (Salmo salar, L.) underad libitumfeeding regime

Abstract

Fifteen experimental diets with five levels of medium chain triglycerides (MCT) (0, 39, 78, 117 and 156 g kg−1) and three levels of cysteine supplementations (0.0, 2.5 and 5.0 g kg−1) were fed ad libitum to Atlantic salmon (mean weight at start 846 g) in sea water for 71 days. Nutrient digestibilities and protein retention improved significantly with increasing dietary MCT level following simple linear regression models. Positive effects were also observed on proteolytic enzyme activities in chyme of the pyloric region with peak value around 117 g kg−1 MCT. However, strong inverse relationships were observed between MCT level and feed intake, growth, body lipid and energy retention, and these effects accelerated with increasing MCT level. Also chyme dry matter decreased with increasing MCT level which also seemed to stimulate pancreatic and bile secretion. MCT did not significantly affect condition factor, dress out percentage, relative liver size or pH in gastrointestinal contents. The only significant effects of dietary cysteine supplementation were increased enzyme activities in chyme of the pyloric region with peak values for the intermediate cysteine level. The results elucidate the importance of diet composition for digestive functions, production efficiency and composition quality.

Evidence of a metabolic fatty acid-sensing system in the hypothalamus and Brockmann bodies of rainbow trout: implications in food intake regulation

“…Besides their role as an energy source, lipids have been shown to act as important signaling molecules in mammals (28). In fish, high levels of circulating lipids have been traditionally associated with reduced food intake (15,17,32,49,51,56), while more recently, a deleterious effect on glucose homeostasis has been described in rainbow trout fed a high-fat diet (12). However, these effects had never been evaluated before using individual FA.…”

“…FA metabolism only accounts for part of FA sensing in mammalian hypothalamus since alternative mechanisms have been suggested to be present, such as binding to the FA transporter CD36 (32), which would act as a receptor rather than a transporter (29). The participation of CD36 on this mechanism was evaluated in rainbow trout by assessing changes in its mRNA abundance, which was enhanced in hypothalamus by the oleic acid administration without being affected by octanoic acid treatment.…”

Criteria for Safe Use of Plant Ingredients in Diets for Aquacultured Fish

“…Adding 17% tricaprylin (C 8 ) of the diet to rainbow trout depresses growth and nutrient digestibility compared to fish oil controls . In Atlantic salmon, including more than 10% MCT into the diet (mixture of C 8 and C 10 ) appears to reduce growth, feed intake and energy retention (Nordrum et al 2003). The response of the fish to MCT depends on the type of MCT administered.…”

“…They will also reduce muscle lipid content in a dose-dependent manner Nordrum et al 2003 . Further increases (>10%) in the level of MCT will have negative impacts on the fish.…”

Carbohydrates in fish nutrition: digestion and absorption in postlarval stages

“…These brush border enzymes can also be detected in the lumen content (Fagbenro et al. 2000; Nordrum et al. 2003), most likely because of shedding of mucosal tissue.…”