Spawning
Cobia reach sexual maturity within 2 years of age under aquaculture settings.
Mature broodfish are multiple spawners with a protracted spawning season from mid-spring to mid-autumn. Photothermal manipulation (27–28oC; 14–hour photoperiod) maximises ovarian development.
Hormone therapy using pelletised implants of luteinising hormone-releasing hormone analogue (LHRHa) can be used to induce final oocyte maturation, ovulation, and spawning in broodfish.
Groups of selected spawners are placed in a separate tank and spawn 37–40 hours after implantation.
Note: Many chemicals used in aquaculture, including hormones like LHRHa require veterinary advice and prescriptions before use.
Egg production
Females typically release more than 2 million eggs per group spawning event.
Fertilised eggs:
- are spherical and buoyant and hatch 22–24 hours after fertilisation at 27–28oC
- can be transported to hatcheries at the gastrula stage (~12 hours post fertilisation) in oxygen-pressurised aquarium bags with minimal impact on hatching success.
One day post hatch larvae are about 4mm (standard length) and exhibit first feeding by 3 days post hatch (4.5–4.8mm standard length).
Fingerling production
You may use several larval rearing and nursery phases to produce cobia fingerlings.
Larvae are:
- stocked at up to 50 larva per litre into intensive rearing tanks preferably containing live microalgae
- reared with successions of enriched rotifers and Artemia to 12–14 days post hatch (8–10mm standard length) before being transitioned to manufactured weaning diets
- graded regularly to alleviate cannibalism, which is a significant early mortality factor.
Alternatively, larvae can be transferred to extensive pond systems to feed on zooplankton (e.g. copepods) stimulated to bloom by application of inorganic and organic fertilisers.
At 25 days post hatch metamorphosis nears completion and fingerlings can be mobilised or harvested at 35–40 days post hatch (70–85mm standard length) into indoor, recirculating systems or secondary nursery phase outdoor ponds.
