The tripletail, Lobotes surinamensis, is a pelagic fish commonly found in coastal waters of the Gulf of Mexico and the US South Atlantic region. The species is one of the emerging candidates for the US marine aquaculture industry due to its fast growth rate and praised flesh quality. Efforts to develop aquaculture methods for tripletail to date have included studies of captive spawning, larval culture, and pilot growout trials conducted at low density. Spontaneous spawns of tripletail are infrequent and display low or no fertility. Hormonal induction of males and females selected at advanced stages of oocyte pre-maturation using gonadotropin releasing hormone analog (GnRHa) implants led to large egg releases but fertility remained very low, suggesting inhibitions affecting spawning in culture also impact response to GnRHa treatments.
In this work, the effectiveness of various hormonal induction treatments was evaluated in two series of trials. All trials employed tripletail broodstocks maintained under a photothermal cycle simulating conditions in Mississippi coastal waters during the spring and summer maturation periods. Hormonal therapies were administered to single pairs featuring one female selected with fully grown oocytes and one male. Two pairs were selected among the broodstock every week, administered one of the tested treatment, and isolated in one of two spawning tanks for monitoring of spawning activity and spawn parameters for 5 days. Each treatment was evaluated using a total of 5 to 7 pairs in both series of trials. The first experiment was conducted in 2019 and 2020 and evaluated (i) a single injection of chorionic gonadotropin (hCG administered at 1,100 IU.kg-1 for females and 550 IU.kg-1 for males), (ii) a GnRHa EVAC implant (75 mg.kg-1 for females, 55 mg.kg-1 for males), (iii) a GnRHa EVAC implant as in treatment (ii) administered with a single injection of 5 mg.kg-1 domperidone, (iv) a treatment identical to (iii) but administered a week following the hCG injection of treatment (i), (v) control (not treatment). The second experiment was completed in 2021 and compared pairs receiving treatment (iii) of experiment 1 to pairs treated with a GnRHa EVAC implant and an injection of 10 mg.kg-1 domperidone.
None of the control pairs and those treated with chorionic gonadotropin spawned. Pairs treated with GnRHa implants only produced spawns with no or very low fertility (average 0.6 ± 1.3%), consistent with previous attempts to induce spawning with this treatment in tripletail. Administration of GnRHa implants with 5 mg.kg-1 domperidone lead to a major increase of fertility (42 ± 32.2% in experiment 1). The treatment with a higher dose of domperidone in experiment 2 improved further the fertility of spawns (65.2 ± 34.5% at 10 mg-kg-1 versus 42 ± 32.2% at 5 mg.kg-1). The number of egg releases, fecundity and viability to hatch and post hatch were also improved when domperidone was administered at 10 mg.kg-1.