Increased ability to compete for food by growth hormone-transgenic coho salmonOncorhynchus kisutch(Walbaum)

Abstract

In salmonids, growth hormone (GH) stimulates growth, appetite and the ability to compete for food. This study tested the hypothesis that increased GH levels in GH‐transgenic coho salmon Oncorhynchus kisutch (Walbaum) increase competitive ability through higher feeding motivation. The transgenic strain of salmon used contained a gene construct consisting of the sockeye metallothionein‐B promoter fused to the type 1 growth gene coding region. The transgenic animals (mean size = 250 g) were F1 individuals. In six consecutive feeding trials, the intake of contested food pellets by size‐matched pairs consisting of one control (1 year older non‐transgenic coho salmon) and one GH‐transgenic coho salmon was compared. Pellets were provided sequentially until neither fish took three consecutive pellets; the identity of the fish taking each pellet was noted. Calculated on the three first pellets offered at each feeding trial, the transgenic coho salmon consumed 2.5 times more contested pellets than the controls, supporting the hypothesis that GH transgenesis increases the ability to compete for food. Overall, the transgenic fish consumed 2.9 times more pellets that the non‐transgenic controls, indicating a high feeding motivation of the transgenic fish throughout the feeding trials. It appears that GH transgenesis and GH treatments can induce similar changes in the feeding behaviour of salmonids. Depending on how transgenic and wild individuals differ in other fitness‐related characters, escaped GH transgenic fish may compete successfully with native fish in the wild.

Integration mechanisms of transgenes and population fitness of GH transgenic fish

“…Previous studies have reported significant differences in morphology between the GHtransgenic salmonids and the controls [32][33][34][35]. Ostenfeld et al [36] and Lee et al [31] suggested that changes in body shape were responsible for reduced critical swimming speeds (Ucrit) of GH-transgenic salmonids.…”

Increased food intake in growth hormone-transgenic common carp (Cyprinus carpio L.) may be mediated by upregulating Agouti-related protein (AgRP)

“…Our results suggested that the altered GH secretion pattern may change the mRNA expression levels of hypothalamic orexigenic factor AgRP I in TG common carp. The constant overexpression of GH transgene can result in increased food intake and feeding behavior (Abrahams and Sutterlin, 1999;Devlin et al, 1999;Duan et al, 2009Duan et al, , 2011Sundstrom et al, 2003), and GH can also regulate food intake by acting on the feeding control centre of the central nervous system (CNS) (Bohlooly et al, 2005). Therefore, we speculate that the constant high levels of hypothalamic and serum GH may have a direct or indirect impact on the feeding regulation centre in the hypothalamus, thereby enhancing appetite and feeding motivation.…”

“…Similarly, elevated GH in transgenic salmon induced heightened feeding motivation, increased food intake and feeding behavior (Abrahams and Sutterlin, 1999;Devlin et al, 1999;Sundstrom et al, 2003). In our previous study, we also found that TG common carp consumed more food during competition with normal common carp of the same size, and that this was associated with higher social status and enhanced feeding motivation (Duan et al, 2011).…”

“…In addition, GH treatment resulted in increased food intake and feeding behavior in normal fish (Johnsson and Bjornsson, 1994). Similarly, GH-transgenic (TG) fish, with constantly high levels of GH, exhibit accelerated feeding motivation, higher social status, and increased feeding competitive ability (Abrahams and Sutterlin, 1999;Devlin et al, 1999;Duan et al, 2009Duan et al, , 2011Sundstrom et al, 2003).…”

Gene–environment interactions influence ecological consequences of transgenic animals

“…These transgenic fish overexpress GH and require enhanced feed consumption to achieve the increased growth rates (29). Observations under laboratory conditions have shown GH transgenic fish to be more competitive (30), less discriminate in choosing prey (31), less affected by predator presence when making foraging decisions (32), more likely to attack novel prey (31), and better at using lower-quality food (29) compared with genetically wild relatives. In the natural environment, such physiological and behavioral alterations have the potential to directly influence not only conspecifics through increased competition for food but also prey populations and previously unaffected species through increased predation.…”