Aquaculture production of sablefish (Anoplopoma fimbria) and many other finfishes relies on treating broodstock with synthetic gonadotropin-releasing hormone analogs (GnRHa) for induction and synchronization of spawning. These peptides trigger the release of gonadotropins from the pituitary gland, stimulating gonadal sex steroid (e.g., estrogen and androgen) production and development. Ovaplant (Syndel Laboratories), a synthetic salmon GnRHa pellet has been shown to effectively induce maturation and synchronize spawning in captive sablefish broodstock. However, Ovaplant pellets were recently discontinued and fully replaced with a liquid product, Ovaplant-L (Ov-L). While the same hormone is used for both products, the matrices are quite different, resulting in very different diffusion characteristics. Ovaplant pellets use a cholesterol-based matrix that releases the GnRHa more slowly compared to the sucrose gel-based (liquid) matrix in Ov-L. The faster release and shorter duration of hormone exposure using Ov-L may not be as effective in multiple-batch spawners like sablefish.
This study investigated different Ov-L injection protocols to determine if the new product could successfully induce spawning in sablefish and if a particular protocol is more effective. We tested a single-dose Ov-L protocol outlined in the Ovaplant-L INAD (# 13-298) for the first time in sablefish along with a modified (two-dose) protocol that better mimicked the previous slow-release pellets through inclusion of a priming Ov-L dose, followed by a full or half dose to prolong the GnRHa exposure. We conducted two separate trials either using freshly caught sablefish broodstock (held captive ~3 months) or older reconditioned broodstock (held captive > 3 years). Fish were initially ultrasounded to identify broodstock at the appropriate gonadal stage then randomly divided into treatment groups (n = 4–5 fish/group). Ultrasound images and blood were collected prior to treatment, followed by weekly ultrasounds to track gonadal development and blood draws at 1, 2, and 6 weeks to determine sex steroid levels in the plasma. For each trial we evaluated the percentage of fish that spawned, days to first spawn, number of spawns, the number of eggs produced and egg quality (based on fertilization and symmetry of cell divisions).
In the freshly caught broodstock group, spawning rates were 100% for fish treated with a single or two-dose regimen of Ov-L. However, in the reconditioned broodstock group, only the two-dose treatment successfully induced spawning. Injection(s) with Ov-L induced increases in blood estradiol levels, with the two-dose regimen eliciting a greater response than the single-dose regimen. No fish spawned in the sham-treated control group from either trial and sex steroid levels were low. Overall, these trials demonstrated that Ov-L treatment can successfully induce spawning in sablefish, and that different injection protocols may be required for freshly caught versus reconditioned wild-origin broodstocks. This research was supported by NOAA Office of Aquaculture through Internal Competitive Aquaculture Funds (ICAF).