Volitional tank spawning of domestic striped bass (Morone saxatilis) using human chorionic gonadotropin (hCG) and gonadotropin releasing hormone analogue (GnRHa)- induced ‘pace-setting’ females

Seventy-one tank spawning trials were conducted to evaluate the efficacy of exogenous hormone compounds and a novel “pace-set” strategy for inducing volitional tank spawning behavior in 5th generation domestic striped bass. Female fish (4.74 ± 0.73 kg; mean ± standard deviation) were treated with human chorionic gonadotropin (hCG; 29 trials), gonadotropin releasing hormone analog (GnRHa; 39 trials) or received no hormone treatment (control; 3 trials). Spawning trials were conducted using single females placed in spawning tanks with two (12 trials) or three (38 trials) males or with paired females placed in spawning tanks with three (4 trials) males. Significant differences in egg production, fry production, hatching rate, and fry/kg female body weight were generally not observed between exogenous hormone treatment groups (alpha = 0.05), with the exception of egg production differing between paired females spawning with three males (Student's t-test, p = 0.0255). However, a trend suggesting that increasing the number of males or females within the tanks improves yield of larvae (fry/kg female body weight) was observed. The untreated control females failed to spawn within 7 days. The pace-set spawning was conducted whereby one female treated with either hCG (7 trials) or GnRHa (7 trials) was placed in a spawning tank with one untreated female and multiple males. The results of these trials show for the first time that a hormone-induced female striped bass can be used to stimulate successful volitional spawning of an untreated female in the same tank with fry/kg female body weight production similar to that of hormone-treated fish. Microsatellite-based parentage of select tank spawns and four additional trials conducted with an increased number of males (19 trials total) showed that female striped bass typically spawn with at least two males; a single pair mating was only observed for one spawning trial. These data allowed for the determination of effective broodstock size (Nb) of each tank spawning trial at between 2.00 and 5.60 when considering all male contributions. The Nb generally increased as the number of males and female fish in the tank increased (from 2.53 for one female and two males to 5.52 for two females and six males). These results indicate that domestic striped bass are promiscuous and will generally reproduce in captivity using tank spawning procedures that allow for a high level of genetic diversity to be retained among the offspring. The pace-set method reduces hormone use and may be applied to commercial striped bass production as well as captive spawning of other fish species.