Broodstock of Gulf killifish Fundulus grandis (initial mean [6SD] weight ¼ 8.2 6 1.6 g) were held in static outdoor tanks at a 2:1 (female : male) sex ratio and at densities of 15, 30, or 45 fish/m 3 . Eggs were collected twice per week from spawning mats suspended 8 cm below the water surface. Collected eggs were measured volumetrically and assessed for total number, egg size, and embryo viability. Significantly more eggs were collected from tanks with manufactured (Spawntex) spawning mats than from tanks with cured Spanish moss spawning mats. Significant differences in the mean number of eggs collected were present among density treatments in April, June, and July. Stocking density was also associated with mortality; the greatest mortality was observed in tanks at the highest density (45 fish/m 3 ). There was a clear pattern in egg production in relation to lunar phase, with egg production peaks occurring between full and new moon phases for all three stocking densities. Mean gonadosomatic index values differed significantly among sampling months for both females and males. Analysis of ovaries via histological sections indicated trends in oocyte stages that correlated to continued egg production for this fractionally spawning species. Peak egg production occurred between April and mid-May, when mean (6SD) weekly water temperatures ranged from 23.8 6 1.78C to 28.2 6 1.28C. During April, the mean daily number of eggs collected translated to a reproductive output of approximately 0.90, 0.72, and 0.76 eggs/g of female for stocking densities of 15, 30, and 45 fish/m 3 , respectively. Based on egg output and mortality over the 5-month spawning period, the intermediate density (30 fish/m 3 ) appeared to provide the optimum number of eggs per individual over time for Gulf killifish broodstock held in static outdoor tanks at a 2:1 female : male sex ratio.

A number of aquaculture species, including channel catfish Ictalurus punctatus, are fed high proportions of soybean meal in their diet. We have investigated the potential for the most common phytoestrogen in soybean meal to alter phenotypic sex during sexual differentiation in channel catfish. Channel catfish were fed four dietary concentrations of the phytoestrogen genistein (0, 2, 4, and 8 mg g(-1)) to determine its effect on gonadal sex differentiation. The four treatment diets were fed to sexually undifferentiated channel catfish between 5 and 140 days post hatch (dph) and between 60 and 150 dph. Phenotypic sex was determined by histological examination of the gonads. Ethoxyresorufin-O-deethylase activity was not significantly different among the treatment and control groups. Phenotypic sex was significantly dependant on dietary phytoestrogen concentration (P = 0.01). Additionally, logistic regression showed a significant relation between genistein concentration in the diet and gonadal sex (P = 0.02). Intersex individuals were present at all treatment concentrations, with increasing proportions of intersex fish as the genistein concentration increased for individuals fed treated diets between 5 and 140 dph. Increased proportions of phenotypically male individuals resulted from chronic dietary exposure to the estrogen mimic genistein. There were no significant differences in the proportions of males and females between feed treatment durations. These findings establish that dietary concentrations of genistein can alter sex ratios in cultured channel catfish populations and demonstrates the need to further understand the actions of this and other prominent phytoestrogens in aquaculture species.

Gulf killifish Fundulus grandis have evolved the ability to utilize air incubation in marsh grass to protect embryos from aquatic predators and allow for synchronous hatching during the following diurnal peak tide. This incubation strategy provides a humid, oxygen‐rich environment for the embryos to develop. The current project investigated practical materials that could be used in an aquaculture setting to mimic the air incubation strategy at different salinities, and determined the effect of substrate (moistened with 7.5‐g/L salinity water) on embryo size after an extended incubation period (19 d) at 22°C. Air‐incubated embryos were placed on synthetic foam, bamboo batting, or burlap cloth substrates. Substrates were moistened with 3.5‐, 7.5‐, 14‐, 20‐, or 27‐g/L‐salinity water, and hatching was induced by submersion in water after 19 d of incubation. Embryos incubated in water (3.5‐ and 7.5‐g/L salinity) at the same temperature began hatching at 8 d and continued intermittently until 14 d. These water‐incubated embryos had a hatch rate (mean ± SE) of 44.2 ± 1.1% in 3.5‐g/L‐salinity water and 49.1 ± 0.5% in 7.5‐g/L‐salinity water. The percentage of air‐incubated embryos that hatched was significantly affected by both substrate and salinity. For all air incubation substrates, the 7.5‐g/L salinity treatment provided the numerically highest overall percentage of hatched embryos, 69.9 ± 3.6%, 69.9 ± 6.5%, and 73.8 ± 4.6% hatching on foam, bamboo, and burlap, respectively. Overall, the foam substrate had the highest hatch rate among salinity treatments. Embryo size at hatch was assessed at the 7.5‐g/L salinity for water and all air incubation substrates. The air‐incubated larvae were found to be significantly larger than their water‐incubated counterparts, and foam‐incubated larvae had the smallest abdominal area. Air incubation of Gulf killifish eggs on foam substrate can be used as a production tool to produce larvae that can be synchronously hatched after an extended incubation period.

This study examined whether the soya phyto-oestrogen genistein would have an effect on spermatozoa quality and in vitro fertilization capacity in mature channel catfish Ictalurus punctatus or walleye Sander vitreus. For both species, motility time and motility rank were significantly different among treatment groups and control, with higher genistein concentrations producing significantly lower motility time and motility rank (P 0Á01). Walleye and channel catfish ATP content was significantly lower compared to control treatments at several incubation concentrations and was significantly related to fertilization rate. Fertilization rate was significantly dependant on genistein incubation concentrations (P 0Á01). Additionally, logistic regression showed a significant negative relation between genistein concentration and fertilization in channel catfish (P 0Á01). These results establish that genistein could play a role in reproductive performance within aquaculture species. In addition, these findings warrant further examination of the impact of phyto-oestrogens in broodstock feeds. #