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 the present study is to create Trojan YY supermales as a novel strategy to mitigate Sacramento Pikeminnow populations. The specific objective of this study is to determine when juvenile Sacramento Pikeminnow gonads start to differentiate. With this information, we will know when to start feeding them hormones to manipulate their sex.
Sacramento Pikeminnow collected from the Eel River of all ages and sizes were dissected and had their gonads removed. Small gonads that were unidentifiable under a microscope were kept for histology. These unidentifiable samples were usually collected from fish that ranged in size from >10-20 cm. The tissues were embedded with paraffin wax, and then stained with Hematoxylin and Eosin dye.
Preliminary results show that fish smaller than 15 cm have undeveloped gonadal structures. Hormonal sex reversal should be applied during this period of sexual differentiation. Our future study will be feeding estradiol to fish smaller than 15 cm to produce an XY female that would be crossed with an XY male for the end production of YY fish.