Effects of exposure to culture in fishes: the existence of common morphological responses among species, and their impact on the interaction between escapee and wild Atlantic cod (Gadus morhua)

Wringe, Brendan F. (2016) Effects of exposure to culture in fishes: the existence of common morphological responses among species, and their impact on the interaction between escapee and wild Atlantic cod (Gadus morhua). Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

A major concern regarding the impact of aquaculture is the alteration or reduction of the fitness of wild stocks through interbreeding with escapees. Cultured fishes develop morphologies and behaviours different than those of their wild counterparts, and the spawning success and fitness of cultured fish is frequently lower. However, successful interbreeding between wild and cultured fish is well documented and can lead to negative consequences for the wild population. In this thesis I examined how culture affects the phenotypes of fishes, and how these differences in phenotype in turn relate to reproductive success and offspring early growth and survival. I found that cultured Atlantic cod (Gadus morhua) had relatively smaller fins, heads, eyes, and jaws, but greater condition factor and body depth than wild cod from the same ancestral population. This suite of morphological differences is often referred to as the “cultured phenotype”, and while commonly asserted to exist I was the first to formally test for it using a meta-analysis and a vote-counting analysis. These analyses confirmed that aspects of a general “cultured phenotype” exist. To evaluate the influence of morphology and behaviour on male spawning success, I studied the reproductive interactions of individual cultured and wild male cod in the presence of a cultured female. Despite phenotypic differences, the spawning success of cultured males did not differ from that of wild males. Finally, because the introgression of genetically differentiated escapees into wild populations can lead to fitness declines, I tested the effect of hybridization between two genetically distinct populations of cod. I found no evidence that the pure strain and F1 hybrids differed in their relative fitness, or of differential response to temperature. Finding equal reproductive success of cultured and wild male cod, at least in my experimental conditions, and no differences in early life history fitness between F1 hybrids and non-hybrids suggests that the potential for introgression may be higher than has been predicted by previous studies.

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