VOLITIONAL TANK SPAWNING OF FEMALE STRIPED BASS WITH MALE WHITE BASS PRODUCES HYBRID OFFSPRING

We report the first volitional tank spawning of female striped bass Mo rone saxatilis with male white bass M. chrysops. The female striped ba ss were reared for 6 or 8 years from larvae to mature adults in captiv ity. The wild-caught male white bass were acclimated to captivity 1 ye ar before spawning trials. The fish were induced to mature with implan ted pellets containing synthetic analogue of mammalian gonadotropin-re leasing hormone, [D-Ala(6)-Pro(9)-NEt]-LHRH, at 10 mu g/kg body weight in a cholesterol and cellulose matrix. Males later received an additi onal injection of human chorionic gonadotropin at 500 IU/kg body weigh t to maintain spermiation. At hormone implantation, females were in an advanced state of maturity with oocyte diameters ranging from 650 to 1,000 pm and males were producing milt. Eight females were placed in t anks with three or six males for spawning. Three females did not relea se eggs within 14 d. The remaining five females spawned, but only two produced fertilized eggs and hybrid offspring. All spawnings had large numbers of overripe eggs, which suggests that striped bass females ha d a behavioral aversion to spawning with white bass males.