In recent years, numerous cases of morphological gonadal alterations in fish have been recorded throughout the world and across a wide range of species. In the whitefish Coregonus fatioi from the pre-alpine Lake Thun (Switzerland), the frequency of gonadal alterations is particularly high and the variety of alteration types large. Little is known about the proximal causes and the direct consequences of these morphological features on population persistence. In particular, the potential for the observed alterations to be the phenotypic expression of reduced genetic quality has not yet been addressed. In this study, we used offspring survival during embryogenesis as a proximate indicator of male genetic quality and tested whether the presence of gonadal alterations in males is an indicator of reduced quality. Embryos resulted from in vitro fertilizations of gametes from 126 males and females. We found no significant correlation between embryo survival and gonadal alteration in adults. Our findings suggest that in C. fatioi of Lake Thun, alterations in gonad morphology are not a phenotypic expression of variation in genetic quality.
KEY WORDS: Gonadal alterations · Genetic quality · Embryo survival · Whitefish · Lake Thun
Resale or republication not permitted without written consent of the publisherDis Aquat Org 81: 119-125, 2008 et al. 2005) are known for occasionally hosting intersex individuals, i.e. individuals characterized by the simultaneous presence of both male and female gonadal features (Nolan et al. 2001). However, the prevalence of some types of gonadal alterations is much higher in Lake Thun than in other Swiss waters. Lake Thun therefore appears as a unique case with respect to both the large variety of deviations and their high frequency (Bernet et al. 2004). Over a 3 yr period of sampling, Bernet et al. (2004) recorded that 35% of whitefish (281 out of 808 fish) were affected, among them males and females of all age classes, from 1 to 6 yr, and individuals of different species (see Douglas et al. 1999 for a discussion of the taxonomy of Alpine whitefish). The deviations observed in these individuals included fusions to the trunk musculature, asymmetries, compartmentations, constrictions atrophy/aplasia and intersex (see Bernet et al. 2004 for a precise description of these alterations).The reasons for the observed patterns are not clear yet, but several factors may individually or jointly affect gonadal morphology and development in fish. Hybridization, i.e. the mating of individuals from different species or subspecies, appears to be one of them (Chevassus 1983). Among the known environmental factors, temperature, parasites, and chemical substances are often cited as primary determinants (reviewed in Blazer 2002). Finally, hatchery management might add to the aforementioned exogenous factors. In particular, fertilization practices, such as single male or sequential fertilizations (Wedekind 2002, Wedekind & Müller 2004), may decrease the overall genetic quality of individual fish, whic...