Adiposity and growth of post-smolt Atlantic salmon Salmo salar L.

Abstract

The long‐term adipose homeostasis seen in mammals gives rise to a ‘lipostatic’ model in which signals produced in proportion to fat stores serve to regulate energy intake. An extension of this predicts an impact of these signals on growth; downregulation of feeding in animals with increased adiposity should result in reduced growth. This was tested by monitoring fat deposition and growth in Atlantic salmon Salmo salar L. provided with feeds that differed in fat content. Salmon parr (mass c. 20 g) were fed either high‐ (H: 34%) or low‐fat (L: 22%) feeds, based on either fish (F) or vegetable (V) oils for 6 months to create groups of fish that differed in adiposity (10–12% and 5–7% body fat) at parr–smolt transformation (mass c. 130 g). Fish fed the high‐fat feeds deposited more body fat, and this was confirmed by measurement of fat concentrations in the fillet, viscera and remaining carcass. The fish were then grown‐on in sea water (c. 35 g L−1, 8 °C, 24L:0D) for 14 weeks while being fed either high‐ or low‐fat feed formulated with fish oil to give the following treatments: HF→ H, HF→ L, LF→ L, LF→ H, HV→ H, HV→ L, LV→ L, LV→ H. Although fish exposed to the various feed treatments did not differ markedly in growth rate (SGR range 1–1.14% day−1) over the 14 weeks of rearing in sea water, the results were in general agreement with predictions from the ‘lipostatic’ model, i.e. fish with the greatest fat reserves after the parr–smolt transformation grew more slowly than fish that were ‘leaner’ at this time. This suggests that adiposity, or ‘fatness’, may exert a negative feedback on feeding in salmon, thereby having an influence upon growth.

Feeding ecology of early marine phase Atlantic salmon Salmo salar post-smolts

“…Larger hatchery‐reared post‐smolts in this population also have greater energy reserves in the form of adipose tissue than smaller individuals from natural and semi‐natural rearing. This adiposity has a negative influence on growth rate in the post‐smolt phase (Jobling et al , 2002) and smaller, leaner fish may grow faster upon marine entry thereby improving survival despite an initial size disadvantage. This size effect suggests that smaller post‐smolts were more efficient foragers than larger individuals.…”

Fish oil replacement in finfish nutrition

“…However, the fat storage location in the body differs among species (Hardy et al. 1987; Jobling et al. 2002; Sargent et al.…”

“…Jobling et al. (2002) reported that the proportion of some of the typical fatty acids commonly found in VO (i.e.…”

“…Consequently, the authors suggested that it was possible to use the fatty acid profile to discriminate between fish that had different dietary histories during rearing in fresh water. Jobling et al. (2002) concluded that during the finishing period, the decrease in the proportion of some fatty acids typical of VO either resulted from lipid turnover and fatty acid metabolism or more likely from ‘dilution’ occurring from lipid deposition as the fish increased in size.…”

Immunohistochemical and immunological detection of ghrelin and leptin in rainbow trout Oncorhynchus mykiss and murray cod Maccullochella peelii peelii as affected by different dietary fatty acids

“…The finding that leptin circulates in plasma in proportion with body adipocytes led to the theory that this protein acts as an “adipostat,” a humoral signal carrying information regarding energy reserves (Brennan and Mantzoros,2006). In the Atlantic salmon ( Salmo salar ), it has been reported that, following parr‐smolt transformation, fatter fish show grow retardation compared to leaner specimens (McCormick,2009), suggesting that adiposity, and perhaps a leptin‐like factor, exerts a negative feedback on feeding and further supports the speculation that leptin may induces an overall increase in fat metabolism in fish (Jobling et al,2002; Londraville and Duvall,2002).…”