No abstract

Growth and survival of fingerling Atlantic sturgeon, Acipenser oxyrinchus, were examined at three different feed rates. Sturgeon (mean initial weight±SD of 28±12 g) were offered a closed-formula, commercially-available sturgeon diet (48.5% protein, 16.2% fat, 9.9% moisture, 7.6% ash, 0.5% fiber and 17.4% nitrogen free extract) via 24-hour, time-controlled feeders at rates of 1.5, 3.0, and 4.5% body weight per day (BW/day). Mean water temperature was 16.8°C. After 49 days of feeding, final length, final weight and feed conversion were all significantly affected by feeding rate (P Յ 0.05). Peak feed conversion occurred at a ration of 1.5%, while maximum increase of both length and weight occurred at approximately 3.0%. No mortality occurred during the seven-week trial. The choice of feeding rates will ultimately depend upon production requirements and the culturist. Offering diet at a rate of 3.0% BW/day will result in significantly greater growth accompanied by high survival. Delivering diet at a rate of 1.5% BW/day will result in equally high survival and require approximately 50% less diet. It will, however, yield lower growth rates.

The effects of four extenders on the fertilization rates of eggs fertilized with cryopreserved sperm of Atlantic salmon Salmo salar were tested. We used (1) glucose extender (54.04 g glucose/L and 1.7 g KCl/L) with 5% DMSO, (2) glucose extender with 5% DMSO supplemented with 13.3% egg yolk, (3) glucose extender with 10% methanol, and (4) glucose extender with 10% methanol supplemented with 13.3% egg yolk. Fertilization rates, expressed as the percentage of eyed embryos, ranged from 52.7% to 83.5%. Sperm cryopreserved with the glucose extender and 10% methanol supplemented with 13.3% egg yolk yielded significantly higher fertilization rates (83.5%) than did sperm cryopreserved with the other three extenders. Our fertilization rates compare favorably with those observed for eggs from the same year-class fertilized with fresh milt (81.4%) and reared at the White River National Fish Hatchery. The presence of egg yolk in extenders incorporating 10% methanol provided additional protection to salmonid sperm during the freezing and thawing processes and resulted in an increase in survival from 72.9% to 83.5%. However, the cryoprotective effect of egg yolk may be specific to the individual formulation of extenders. In our trials, glucose and 5% DMSO without egg yolk yielded a 66.9% fertilization rate, while glucose and 5% DMSO supplemented with 13.3% egg yolk produced only 52.7% fertilization after cryopreservation.

Because of disease transmission concerns, field studies to evaluate the impact of water-hardening eggs at different concentrations of polyvinylpyrrolidone iodine (iodophor) for various times of exposure have rarely used untreated controls. Additionally, U.S. Fish and Wildlife Service protocol requires a subsequent post-water-hardening surface disinfection for salmonid eggs transferred between stations. The cumulative impact of this second disinfection on survival has not been fully investigated for Atlantic salmon Salmo salar. This study compared the percent of eye-up Atlantic salmon eggs that had been water-hardened with iodophor treatments at 50, 100, and 150 mg active ingredient/L for 30, 60, and 90 min with that of untreated controls and also examined the impact on egg survival of a second iodophor disinfection 5 h after the initial exposure. No discernable mortality resulted from the second (10-min) disinfection. Nontreated eggs had significantly greater survival than any of the iodophor-treated eggs. Contact time with the iodophor solution had the greatest impact on egg survival. When averaged over all concentrations, the decline in egg survival was significant (P Ͻ 0.05) when contact time increased from 30 to 60 min. Interaction between iodophor concentration and exposure time was most evident at the high (150 mg/L) concentration, with egg mortality increasing with contact time.Our study suggests that to optimize egg survival, contact with iodophor during water hardening should be no more than 30 min. If a greater disinfection efficacy is desired, an increase in iodophor concentration may be preferable to an increase in contact time.