Sacramento Pikeminnow (Ptychocheilus grandis) are a large (up to 1.4m) piscivorous cyprinid native to the Sacramento-San Joaquin basin in California. They were introduced in the upper mainstem of the Eel River, CA in 1979. Over time, it has become one of the most prevalent fish species within the Eel River ecosystem, raising concerns due to its predation and competitive interactions with juvenile salmonids and other native fishes. Because of this, there have been many suppression efforts to eradicate the Sacramento Pikeminnow populations in the Eel River, but none of them have been successful in reducing their populations in a meaningful way. Despite the Sacramento Pikeminnow being as abundant as they are, there is very little information on their life history and especially on their reproduction. The overall goal of this study is to create Trojan YY supermales, male fish with YY chromosomes that only produce male offspring, as a new method to reduce the populations of Sacramento Pikeminnow. By skewing the population’s sex ratio, this approach aims to eventually decrease the overall population size and even eradicate the species entirely in the river. The specific objective of this study is to test the duration and dose needed to create XY female Sacramento Pikeminnow using 17β-Estradiol.
Histology revealed that Sacramento Pikeminnow gonads begin developing at 14 cm. In this preliminary study, 30 juvenile Sacramento Pikeminnow (8-10 cm) were used to test the duration and dose of 17β-estradiol needed for sex reversal. The fish were housed in a 130 L circular tank and maintained at 20°C. The 17β-estradiol was initially mixed into their feed at a dose of 50 mg/kg using ethanol, but the fish refused to eat. Switching from ethanol to fish oil as the carrier improved feed acceptance. Three treatment durations were tested: 60, 90, and 120 days. After each period, 10 fish were transferred to their own 130 L tank.
Because gonads are difficult to locate in Sacramento Pikeminnow under 15 cm, the fish will be elastomer-tagged to differentiate between trials and moved to 2120 L tanks for further growth before dissection.