Traditional marine finfish aquaculture utilizes captive male and female broodstock to provide fertilized eggs for nursery and growout operations. This presents challenges for grouper aquaculture, especially in the United States where there are no hatcheries for any grouper species. Grouper are protogynous hermaphrodites (i.e. mature first as female and then transition to males) with a single large male controlling a harem of smaller females. This is problematic when trying to capture male broodstock because males typically live in deeper water (e.g. > 30m depth) and experience barrow trauma as the gas bladder expands during capture. Females are much easier to capture because they are more abundant and live in shallower water. However, expecting females to transition into male broodstock in captivity is unrealistic and could take many years, if ever. Therefore, finding alternative grouper broodstock management strategies for hatchery production could benefit the industry, especially in the US.
An alternative method for grouper broodstock management and fertilized egg production for black grouper (Mycteroperca bonaci) and red grouper (Epinephelus morio) is currently being developed at the Southernmost Marine Aquaculture Research & Training (SMART) Center at the College of the Florida Keys. The concept focuses on the collection of grouper sperm from a variety of sources including: (1) visceral discards from commercial and recreational fishers, (2) collection of sperm during catch-and-release fishing, and (3) captive grouper in public aquaria. Viable sperm are then cryopreserved in liquid nitrogen and stored long-term in a -86°C freezer.
Female grouper are easier to bring into captivity, so special recirculating aquaculture systems are being developed at the SMART Center to control temperature, photoperiod, and lunar cycle, mimicking spawning conditions for M. bonaci and E. mori. Other factors introduced into the broodstock systems include: (1) recordings of spawning behavior, (2) small amounts of grouper sperm from cryopreserved samples, and (3) a combination of both treatments. Fish behavior will be recorded using submersible infra-red cameras and periodic sampling for egg development. If natural egg production is unsuccessful, female grouper will be implanted with OviplantTM (i.e. Salmon Gonadotropin – Releasing Hormone analogue; sGnRHa). Eggs produced will then be mixed with thawed sperm from cryopreserved samples and fertilization rates will be recorded. If successful, the systems and protocols can be applied to other commercially or ecologically important marine species that: (1) exhibit complicated life history strategies, (2) are difficult to spawn in captivity using traditional broodstock management techniques, and/or (3) have eggs, sperm, or gonads that can be easily obtained during commercial or recreational fishing.