Dietary histidine requirement to reduce the risk and severity of cataracts is higher than the requirement for growth in Atlantic salmon smolts, independently of the dietary lipid source

Abstract

The present study was carried out to investigate whether the dietary histidine requirement to reduce cataract development is higher than that for growth in Atlantic salmon smolts (Salmo salar L.) after seawater transfer and whether dietary vegetable oils contribute to cataractogenesis. Duplicate groups of salmon smolts were fed ten experimental diets with either fish oil (FO) or a vegetable oil (VO) mix replacing 70 % FO and histidine at five target levels (10, 12, 14, 16 and 18 g His/kg diet) for 13 weeks after seawater transfer. The VO diet-fed fish exhibited somewhat inferior growth and feed intakes compared with the FO diet-fed fish, irrespective of the dietary histidine concentration. Both cataract prevalence and severity were negatively correlated with the dietary histidine concentration, while lens N-acetyl-histidine (NAH) concentrations were positively correlated with it. The fatty acid profiles of muscle, heart and lens reflected that of the dietary oils to a descending degree and did not affect the observed cataract development. Muscle, heart and brain histidine concentrations reflected dietary histidine concentrations, while the corresponding tissue imidazole (anserine, carnosine and NAH) concentrations appeared to saturate differently with time. The expression level of liver histidase was not affected by the dietary histidine concentration, while the liver antioxidant response was affected in the VO diet-fed fish on a transcriptional level. The lowest severity of cataracts could be achieved by feeding 13·4 g His/kg feed, independently of the dietary lipid source. However, the present study also suggests that the dietary histidine requirement to minimise the risk of cataract development is 14·4 g His/kg feed.

Lens metabolomic profiling as a tool to understand cataractogenesis in Atlantic salmon and rainbow trout reared at optimum and high temperature

“…In the present study, both species were fed the same diet, designed to cover the dietary amino acid requirements for growth for both species, with a dietary histidine concentration of 10 g His kg -1 feed. This concentration is however lower than the re-established requirement of 13.4 g His kg -1 feed to minimize the risk of cataract development for Atlantic salmon smolt after seawater transfer [20], and this may explain both the severity of cataracts and the almost depleted lens NAH concentration in Atlantic salmon in the present study. In comparison, the rainbow trout was able to maintain a higher lens NAH concentration, with lens NAH constituting approx.…”

“…Sub-optimal levels of dietary histidine has been identified as a major risk factor for cataract development in farmed Atlantic salmon, and cataracts can be mitigated by increasing the dietary histidine concentration [7,19,20]. The cataract mitigating effect of dietary histidine has been attributed to the synthesis and concentration of NAH in the lens [20, 36]. The concentration of NAH in Atlantic salmon lenses has been shown to reflect the dietary histidine concentration, and a low level of NAH is therefore considered a marker for the risk for cataract development.…”

“…However, in recent years, a high prevalence of cataracts have especially been reported in farmed Atlantic salmon, in relation to low dietary levels of the essential amino acid histidine [7, 18, 19]. In periods when the fish is sensitive, such as after seawater transfer and in periods with high or fluctuating water temperatures, the requirement for histidine to reduce the risk of cataract development appears to be higher than the estimated requirement for growth in Atlantic salmon [7, 19, 20]. Histidine is taken up by the lens and synthesized to N-acetylhistidine (NAH), and the severity of cataracts is negatively correlated with the concentration of NAH in the lens [7, 19, 20].…”

“…In periods when the fish is sensitive, such as after seawater transfer and in periods with high or fluctuating water temperatures, the requirement for histidine to reduce the risk of cataract development appears to be higher than the estimated requirement for growth in Atlantic salmon [7, 19, 20]. Histidine is taken up by the lens and synthesized to N-acetylhistidine (NAH), and the severity of cataracts is negatively correlated with the concentration of NAH in the lens [7, 19, 20]. Lens NAH has been shown to have important roles as an osmolyte [21, 22], buffer component [19] and possibly intracellular antioxidant [23], and is therefore essential in maintaining the lens water balance and cell integrity.…”

Water temperature and dietary histidine affect cataract formation in Atlantic salmon (Salmo salar L.) diploid and triploid yearling smolt

“…; Remø et al . ). The consequence of osmotic imbalance in the lens is the formation of cloudiness that subsequently reduces vision (Rhodes et al .…”