Genetically modified growth affects allometry of eye and brain in salmonids

Abstract

Effects of growth acceleration on eye development have been examined in genetically modified salmonids. Growth hormone (GH) transgenic coho salmon ( Oncorhynchus kisutch (Walbaum, 1792)) show dramatically elevated overall body growth and an absolute increase in eye size, but relative eye growth is shifted from negatively allometric to more isometric. Thus, transgenic fish possess significantly smaller eyes relative to nontransgenic fish of the same size. Ration-restricted limitation of growth in transgenic salmon to that of wild type restores relative eye growth rate, suggesting that effects on eyes are an indirect consequence of modification of growth rate rather than a direct effect of GH overexpression. Heart, spleen, and liver did not show changes in proportion among groups, whereas total brain size showed the same response as eye. Relative eye and brain size were also reduced in a fast-growing domesticated strain of rainbow trout ( Oncorhynchus mykiss (Walbaum, 1792)), suggesting modifications of allometry are a more general effect of growth acceleration. GH mRNA levels from the transgene were elevated in eyes, whereas IGF-I mRNA was not, suggesting this organ may be regulated in a different fashion than other organs. Neural tissues with critical structural requirements for optimal function may be subject to less modification of growth rate than are other organ systems.

Rapid morphological divergence of cultured cod of the northwest Atlantic from their source population

“…Apart from simply being proportional to the head size, Devlin et al (2012) have suggested that the eye development of rapidly growing fish becomes decoupled from their somatic growth, resulting in a negative allometry.…”

Effects of Growth Hormone (GH) Transgene and Nutrition on Growth and Bone Development in Common Carp

“…In a previous study of our laboratory, we had found that transgenic carp had 6.36 times higher serum GH level than the nontransgenic fish (Duan et al, ), which may have resulted in the reduced growth rate of the pharyngeal bone in the transgenic carp. It could be due to a de‐coupling between somatic growth (strongly stimulated by GH) and pharyngeal bone growth (less strongly stimulated by GH) similar to that found for coho salmon eye and brain growth (Devlin et al, ; Kotrschal et al, ).…”

Accuracy of nonmolecular identification of growth‐hormone‐transgenic coho salmon after simulated escape

“…The criteria used and the scoring outcome strongly suggest that the raters used traits easily recognized from transgenic fish reared only in the hatchery. Typically, fast-growing hatchery-reared transgenic fish have smaller eyes and heads, large, bulging abdomens, and a higher condition factor from the larger amount of food consumed compared to wildtype fish (Ostenfeld et al 1998, Devlin et al 2012. Such changes in phenotype are highly dependent on indirect effects of enhanced growth rate, since the characteristics are much reduced in transgenic animals forced to grow at a wild-type rate by ration restriction (Devlin et al 2012).…”

“…Typically, fast-growing hatchery-reared transgenic fish have smaller eyes and heads, large, bulging abdomens, and a higher condition factor from the larger amount of food consumed compared to wildtype fish (Ostenfeld et al 1998, Devlin et al 2012. Such changes in phenotype are highly dependent on indirect effects of enhanced growth rate, since the characteristics are much reduced in transgenic animals forced to grow at a wild-type rate by ration restriction (Devlin et al 2012). These traits had already developed in the Th group after three months in the hatchery and were still easily observable even after 10 months in the stream environment.…”

“…When transgenic and wild-type fish are fed the same amount of food under hatchery conditions (i.e., pairfed), transgenic fish are longer and leaner for the same mass (reduced condition factor), whereas if these fish are then fed to satiation, they will rapidly outgrow wild type and exhibit increased condition (Raven et al 2006). However, when fed to satiation, the head of the transgenic fish does not grow isometrically with the body, suggesting that growth hormone affects the growth of the structures of the head differently from those of the rest of the body (Devlin et al 2012). Thus, it was not unexpected to find that the stream-reared transgenic fish had relatively smaller heads even though they were not necessarily larger than the wild type.…”