Macroscopic gonadal deviations and intersex in developing whitefish Coregonus lavaretus

Abstract

In Lake Thun, Switzerland, a significant number of whitefish Coregonus lavaretus were found to exhibit abnormal gonadal morphology. To determine the time at which the morphological deviations from a normal gonadal arrangement develop, we conducted experiments designed to: (1) examine whether the morphologic gonadal variations develop during or after gonadal differentiation, and (2) characterise the entire ontogenetic gonadal development in whitefish from hatching until maturity. For these experiments, whitefish were reared under controlled conditions with distinct water sources and temperature regimes (Lake Thun water: 4 to 22°C; spring water: 8 to 9°C). Gonadal development in the spring water group was clearly delayed with respect to age, but similar to the Lake Thun water group with respect to degree-days in Celsius (°D). Undifferentiated gonads were first seen at 65 d post-hatch and 491°D. Ovarian differentiation (starting from 1734 to 1820°D) preceded testicular differentiation (starting from 1989 to 3673°D). The first fish with mature germ cells were recognised at 8163 to 8356°D. Morphological gonadal deviations became evident during gonadal differentiation. Constrictions and asymmetries developed for the first time in the first (0+) or second (1+) year-of-life, at a body length of 13 to 18 cm. Aplasia and compartmentation were recorded in the third (2+) year-of-life at a body length of 16 to 18 cm. Intersex fish occurred at a frequency of 8 to 9% during gonadal sex differentiation. Because no evidence for the presence of exogenic endocrine active substances was revealed, we suppose that there is a naturally increased mosaic intersex condition in whitefish during the ontogenetic gonadal differentiation process.

Persistent Unequal Sex Ratio in a Population of Grayling (Salmonidae) and Possible Role of Temperature Increase

“…Contamination levels that have been found do not explain the malformations. Moreover, Bernet et al () raised whitefish from a population with gonadal deformation in spring water and on artificial food and found gonadal abnormalities similar to those observed in the wild. These findings suggest that toxicants are not responsible for the unequal OSR we observed.…”

Additive genetic variation for tolerance to estrogen pollution in natural populations of Alpine whitefish (Coregonus sp., Salmonidae)

“…Some whitefish populations in pre-Alpine lakes showed extraordinary high prevalences of gonadal deformations during recent years (Bernet et al. 2009 ). Potential pollution by endocrine disruptors has been a focus of various studies (e.g., Liedtke et al.…”

Endocrine Disruption in Wildlife: Background, Effects, and Implications

“…Instead, it is becoming evident that the feminization of wild fish has a multicausal etiology involving contributions from at least both steroidal estrogens and xenoestrogens and from other (as yet unknown) contaminants with anti-androgenic properties [186]. For example, frequent and unexplained gonadal abnormalities including intersex features have recently been observed in whitefish (Coregonus lavaretus) in a relatively pristine lake in Switzerland with no evidence revealed for the presence of exogenic EDCs [191]. For example, frequent and unexplained gonadal abnormalities including intersex features have recently been observed in whitefish (Coregonus lavaretus) in a relatively pristine lake in Switzerland with no evidence revealed for the presence of exogenic EDCs [191].…”