Controlled cultivation techniques for the recovery of threatened fishes in Virginia

The goal of this research was to develop captive propagation methods for the Federally threatened spotfin chub, Cyprinella monacha, and yellowfin madtom, Noturus flavipinnis, by using closely related, but unthreatened species, to evaluate potential techniques. The surrogate species used were the whitetail shiner, Cyprinella galactura, and the margined madtom, Noturus insignis. I investigated methods to promote gonadal maturation, induce spawning, and rear larvae of these fishes.

Captive whitetail shiners developed mature gonads under a variety of temperature and photoperiod conditions. Spawning condition was maintained for over two years when they were held at constant warm temperature (≈ 24 C) and long photoperiod (16 h light). Whitetail shiners did not readily spawn in aquaria, but were induced to spawn by hormonal injection with human chorionic gonadotropin (hCG) and carp pituitary extract (CPE) at mean dosages of 1688 I.U./kg and 20 mg/kg, respectively, or with luteinizing hormone releasing hormone analogue (LHRHa) and domperidone at mean dosages of 363 µg/kg and 36 mg/kg, respectively. Most females spawned within 30 h of the first injection. Stripped ova were effectively wet-spawned, and larvae hatched in 8 d at 25 C. I obtained a mean hatch rate of 55 %, but lack of swimbladder inflation resulted in very poor survival of several batches of eggs. Larvae began feeding within 2 d of hatching, and survival rates of 50 to 90 % after 16 d were obtained when larvae were fed twice daily on a diet of brine shrimp nauplii at a rate of ≈ 10/L/d, and a commercially prepared larval fish diet at a rate of ≈ 14 mg/L/d.

Changing photoperiod, but not temperature, was required to induce oocyte maturation in most captive female margined madtoms. Sperm production in mature male madtoms was enigmatic; motile sperm were observed only once. Plasma testosterone concentrations in males peaked just prior to the spawning season at 6.5 ng/mL, but levels were not correlated with male gonadosomatic values. Plasma 17β-estradiol levels in females peaked just prior to the spawning season at 15 ng/mL, and were correlated with gonadosomatic values. Captive margined madtoms did not tank spawn unless they were hormonally injected with hCG and CPE at mean dosages of 5256 I.U./kg and 58 mg/kg, respectively, or with LHRHa and domperidone at mean dosages of 554 µg/kg and 55 mg/kg, respectively. Most females ovulated within 78 h of the first injection. Inclusion of more than one breeding pair per tank inhibited tank spawning. Embryos did not develop in 55 % of tank-spawned ova, or from any strip-spawned ova. Parents consumed spawned egg masses if they remained with the nest. Hatch rates > 65 % were obtained by suspending egg masses in a large-mesh basket over turbulent aeration at 28 to 30 C. Larvae hatched in 7 d at 28 C. Survival rates > 50 % after 15 d were obtained when larvae were fed salmon starter twice daily at a rate of 20 mg/L/d, and tanks were thoroughly cleaned daily.