Growth hormone‐induced effects on mortality, energy status and growth: a field study on Brown Trout (Salmo trutta)

Abstract

1. Growth hormone (GH) treatment increases the growth rate and competitive ability of salmonids under laboratory conditions. Since fast growth should increase fitness, why is endogenous secretion of GH not higher in wild fish? To address this question, three hypotheses were suggested. H1: high GH levels reduce antipredator responses and may therefore increase mortality from predation. H2: high GH levels reduce long‐term (e.g. over winter) survival by reducing allocation to critical energy reserves. H3: GH is not beneficial for growth under natural conditions. 2. To test these hypotheses, the performance of GH‐treated juvenile Brown Trout (Salmo trutta) and control (placebo) trout was compared in an enclosed stream section subjected to natural predation. Four experiments were conducted during winter, spring, summer and autumn, respectively. 3. Mortality rates were not significantly different between GH‐treated and control trout in any of the four experiments so H1 was not supported. Energy reserves were generally lower in GH‐treated fish, which is consistent with H2, whereas growth rates in mass were higher in GH‐treated fish than in controls so H3 was not supported. This suggests that GH promotes growth at the expense of investment in maintenance. 4. Judging from growth and mortality rates, the fitness of GH‐treated and control trout appeared similar. Thus, escaped GH‐manipulated fish may compete successfully with wild fish. 5. Hatchery‐raised trout with higher initial condition index suffered higher mortality rates than more slender fish. This novel finding may be explained by reduced escape ability related to body morphology, reduced behavioural responses towards predators by high‐condition trout, or predator preferences for high‐condition fish.

Population effects of growth hormone transgenic coho salmon depend on food availability and genotype by environment interactions

“…Under favorable conditions, such as high food availability or low population densities, GH transgenic genotypes would be anticipated to grow rapidly with minimal effect on survival. Indeed, experiments examining the effect of GH treatment on salmonids in nature have revealed little effect on survival under normal conditions (34). High growth conditions would favor earlier sexual maturity of transgenic genotypes (12,25), which could facilitate GH transgene introgression into populations.…”

Fitness‐related effects of growth investment in brown trout under field and hatchery conditions

“…These fish had access only to the naturally occurring food. For information on important prey taxa in the stream, see Johnsson et al (1999). The remaining 25 GH-treated and 25 control trout were transferred to an 800-l hatchery tank (1 2 0·4 m) supplied with river water at ambient temperature ( Fig.…”

Characterization of environmental risk of genetically engineered (GE) organisms and their potential to control exotic invasive species

“…The implanted fish could be released into natural environments and their survival rate and other fitness components could be measured (Johnsson et al, 1999;. Unfortunately, it will not be possible to mimic all GE organisms, but the approach could be used to validate the method.…”