Interaction of rearing temperature and maternal influence on egg development rates and larval size at hatch in yellowtail flounder (Pleuronectes ferrugineus)

We assessed the extent to which temperature interacts with maternal contributions to egg size to affect development time and size of yellowtail flounder (Pleuronectes ferrugineus) larvae at hatch. Maternal effects contributed significantly to differences in egg sizes produced by four females. Eggs from each female were incubated at five temperatures. Development time was most significantly affected by temperature, and female effects were minimal. However, the variance in development time within a population was significantly affected by an interaction between female and temperature effects. Average length at hatch varied significantly among temperatures and females, as did the variance in hatching length within a population. Variance in hatching length explained by maternal effects peaked at intermediate temperatures (~38% explained variance at 7°C), while variance explained by covariation with development time increased linearly with temperature, explaining ~40% variance at 13°C. Overall, the nonadditive interaction between maternal contributions and the environment suggests that female effects must be considered over the entire range of environmental conditions experienced by their progeny. In addition, our results support the idea that it is inappropriate to quantify female effects among eggs and extrapolate these differences to larvae.

Gonadotropin-releasing hormone analogue (GnRH-A) induces multiple ovulations of high-quality eggs in a cold-water, batch-spawning teleost, the yellowtail flounder (Pleuronectes ferrugineus)

Sustained delivery systems for a gonadotropin-releasing hormone analogue (GnRH-A) were used for the first time in a cold-ocean teleost for inducing multiple ovulations. Intramuscular implants of 75-224 µg/kg GnRH-A ((D-Ala6,Pro9-NHEt)LHRH) were administered to female yellowtail flounder (Pleuronectes ferrugineus) either as a cholesterol pellet or as biodegradable microspheres. Females implanted with GnRH-A ovulated 3-4 weeks earlier than controls, producing multiple batches of high-quality eggs (average rates of fertilization 66-68% and hatching 55-60%); control fish eggs had significantly lower fertilization (39%) and hatching rates (25%). GnRH-A treatment doubled the egg production, synchronized the females, and shortened the interovulatory periods. The proportion of round, clear, and floating eggs lacking a perivitelline space before fertilization was an indicator of the fertilization (r2 = 0.60) and hatching (r2 = 0.56) success. Moreover, egg collections of less than 10 mL varied greatly in quality, whereas larger batches, generally promoted by GnRH-A, consisted of relatively high-quality eggs. GnRH-A treated fish had increased plasma levels of estradiol-17 beta 4 days after implantation. A model for prediction of the time between hormone treatment and first spawning (T; days) was developed using the initial follicle diameter (D; µm) as the only predictor (T = 365(D - 380)-0.82; r2 = 0.91).