Influence of female age, body size and environmental conditions on annual egg production of the bullhead
A population of bullhead Cottus gobio inhabiting a mountainous river network, was examined for the influence of maternal condition (total length, LT, and age class in years) and environmental factors (water temperature and fish density) on fecundity, egg size and net annual reproductive effort (ER, defined as the ratio of total egg production mass to body mass) within several stocks. Regardless of location within the drainage network, bullhead reproduction was synchronous, with only a single batch and fecundity ranging from 69 to 896 eggs per female. As with LT fecundity increased with age, although the difference between age classes 5 and 6 years was smaller than between other age classes. Egg diameter also increased with age from age classes 2 to 4 years, but then tended to decrease for age classes 5–6 years. Multiple stepwise regression was used to examine the effect of female LT, water temperature and fish densities on bullhead egg production for each of the four age classes (2, 3, 4 and 5–6 years) separately. When statistically significant, water temperature always had a positive effect and fish densities a negative effect, on fecundity and egg size. The LT always had a positive effect on fecundity for all the age classes. In contrast, LT had a positive effect on egg size and ER only for female reaching maturity (2 years), whereas intermediate aged females (3–4 years) were insensitive and the oldest fish showed a negative response.
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Document Type: Regular Paper
Affiliations: CNRS UMR 5023, Ecologie des Hydrosystèmes Fluviaux, Université Lyon 1, 43 Bd du 11 Novembre 1918, 69622 Villeurbanne Cedex, France and
Publication date: 2005-10-01