WEIGHT DEPENDENT INTRASPECIFIC VARIATION IN FEMALE GOLDEN TOPMINNOW Fundulus chrysotus REPRODUCTION

Golden Topminnow (Fundulus chrysotus) are a freshwater species native to the Southeastern United States. This species displays vibrant sexual dimorphism, males with flecks of blue or gold along the body, white or silver underside, and red spots most prevalent in 4-5 rows on the caudal fin. These visual characteristics and relative hardiness have made them a desirable ornamental fish. Aquaculture can be used to prevent wild harvest of the species for the ornamental trade. To determine feasibility of captive reproduction, the issue of low fecundity in Fundulidae must be addressed to maximize output of successful progeny. In this study, we measured reproductive output in terms of egg production, embryo and larval parameters, and total fecundity for three size classes of female Golden Topminnow.

Fish were stocked in 9 outdoor pools at a 2:1 female to male ratio. Three female sizes were selected with mean weights of 3.6, 5.9, and 9.1g, representing small, medium, and large sizes, respectively. Eggs were collected twice weekly from two submerged Spawntex mats per tank. Reproductive output variables recorded included: number of eggs harvested, embryo size, daily hatching, and larval size upon hatching. Embryo and larval pictures were analyzed using Image Tool 3.0 software. At the end of the 13-week outdoor study, 6 females and 3 males from each pool were moved inside to measure determinant fecundity. Following unsuccessful spawning attempts over 3 weeks, palpations for each female were performed on regular collection days for 2.5 weeks (5 palpations/fish).

Mean egg production differed significantly between size classes for 3 of 4 egg collection periods (P < 0.01, 0.01, 0.01; Table 1). Embryos from the large size class females had significantly larger egg shell area (P = 0.01). Larvae from the large size class took longer to hatch (P < 0.01) and were significantly smaller upon hatch (P < 0.01). Fecundity (number of eggs per female per day) normalized by weight fits a power function (Figure 1). Large females, although producing more eggs, may not be producing the most fit individuals.