Atlantic salmon fed a nutrient package of surplus methionine, vitamin B12, folic acid and vitamin B6 improved growth and reduced the relative liver size, but when in excess growth reduced

Abstract

Feeding plant‐based diet through smoltification of Atlantic salmon requires verification of the optimal level of 1C nutrients. Here, we fed Atlantic salmon plant‐based diets containing three different surplus amounts of the 1C nutrients; methionine, cobalamin (vitamin B12), pyridoxine (vitamin B6) and folic acid during 6 weeks in fresh water, through smoltification, followed by 3 months on‐growing period in salt water. The three diets were fed to fish dispersed in triplicate tanks throughout the experiment. Mean start body weight was 32 g. Dietary methionine levels in the diets were 6.7, 9.2 and 11.7 g/kg. Dietary B6 was 6.75, 8.45 and 11 mg/kg. Cobalamin was 0.16, 0.18 and 0.20 mg/kg. While dietary folic acid was 2.9, 4.8 and 6.3 mg/kg, diets are referred to as low, medium and high 1C diet. All other amino acids were similar between diets. The results showed no differences in growth or feed utilization in the fresh water period, but following the on‐growing salt water period, differences between diets occurred. The fish fed the medium 1C diet showed better growth, as compared to fish fed the low or high 1C diet (p = .009). The medium 1C fed fish showed a relative lower liver weight compared with fish fed low or high 1C diet (p = .025). Condition factor was better in fish fed the medium and high 1C diet as compared to those fed the low 1C diet (p = .0006). As expected, free methionine in liver, plasma and muscle increased by dietary methionine inclusion. Surplus vitamins only had minor effect on tissue concentrations. Based on these findings, we conclude that the micronutrient and methionine level presented in the medium 1C diet improved the growth, liver size and condition factor; however, more research is needed to evaluate the optimal requirement level for each of the 1C nutrients.

Metabolic and molecular signatures of improved growth in Atlantic salmon (Salmo salar) fed surplus levels of methionine, folic acid, vitamin B6 and B12 throughout smoltification

“…The feeds were fed in triplicate tanks six weeks prior to smoltification until 3 months after salt water transfer (Figure 1). Pre-smolt salmon (SalmoBreed strain) were randomly assigned to experimental tanks for a two weeks long acclimatization period prior to the start of the experiment as earlier described (7) . Tanks from all treatment groups were placed in random order.…”

“…To avoid poor tank environment, abnormal behaviour and poor welfare, 90 fish per tank were initially kept during the freshwater period (mean body weight of 32.1 g (bulk weight), tank diameter 0.6 m, tank volume 70 L, water flow 300-450 L/hr; rearing temperature 11.9 ± 0.4°C), and then moved to larger tanks for the salt water period (mean body weight of 95.0 ± 3.9 g, tank diameter 0.6 m, tank volume 450 L, water flow 450-900 L/hr; rearing temperature 12.0 ± 0.1°C) (7) . Fish were fed continuously until day 94 of the experiment, and thereafter fed three meals daily for two hours per meal (08:00, 12:00 and 20:00) (7) . The fish received 12 hours light and 12 hours darkness during the first 6 weeks, and continuous light for the rest of the experiment (7) .…”

“…Fish were fed continuously until day 94 of the experiment, and thereafter fed three meals daily for two hours per meal (08:00, 12:00 and 20:00) (7) . The fish received 12 hours light and 12 hours darkness during the first 6 weeks, and continuous light for the rest of the experiment (7) . Fish were vaccinated at day 38 and starved for five days during vaccination.…”

“…https://doi.org/10.1017/S0007114521002336 distress were regularly monitored to avoid suffering. 40 mg/L tricaine (Pharmaq, Norway) was used to anesthetize fish before all handling, and samples were collected from salmon 24 hours after feeding to address effects on metabolism rather than reflecting the feed itself (7) . Tricaine solved in salt water requires no additional buffering, but tricaine solved in fresh water was buffered with 40 mg/L Na 2 CO 3 .…”

“…When salmon was fed the highest surplus level, no additional benefit for growth was reported in the respective trial. Feeding a moderate surplus of 1C nutrients (Med-1C) during the fresh water period, through smoltification until the on-growing salt water period, increased body weight and decreased liver weight of salmon, which was reflected in a higher condition factor and specific growth rate compared to the Low-1C group (7) . The present study compares muscle from Low-1C and Med-1C fed salmon, hereinafter named as Ctrl and 1C+, respectively.…”