Effects of Hypoxia and Elevated Ammonia Concentration on the Viability of Red Snapper Embryos and Early Larvae

The effects of hypoxic conditions and elevated ammonia concentrations on the viability of embryos and newly hatched larvae of the red snapper (Lutjanus campechanus) were investigated. In all experiments, tested levels of hypoxia or ammonia concentrationswere applied to embryos and unfed newly hatched larvae from three different spawns. Exposures began at 1 h post fertilization (pf) and lasted until all individuals in a group had expired. Survival rates were monitored daily in duplicates for each spawn in each treatment. Fertilized eggs exposed to 2 mg L-1 dissolved oxygen (29% saturation) showed complete mortality before hatch while 81% of embryos in control groups (\u3e85% saturation) hatched and subsequently maintained high survival until 5 days pf. Exposure to a moderate hypoxia (target 3 mg L-1, 43% saturation) reduced significantly the hatch rate and subsequent survival rates; the magnitude of the difference in survival rate between control and exposed groups increased from 10% at hatch to 45% at 5 days pf. When oxygen concentration was maintained high (83% saturation) until 36 h pf and then progressively reduced to reach 3 mg L-1 at 2 days pf, the survival of exposed embryos and larvae did not differ significantly from those recorded in control groups, although potential delayed or cumulative effects of the treatment after 4 days pf could not be evaluated in this experiment. Embryos exposed to 10 mg L-1 total ammonia (TA-N), which corresponded to unionized ammonia (UIA-N) concentrations ranging between 0.307 and 0.468 mg L-1 in the conditions of the experiment, exhibited significantly reduced hatch rates and complete mortality between 3 and 4 days pf; the latter period corresponds to the onset of exogenous feeding of red snapper. In contrast, control groups (TA-N \u3c 0.26 mg L-1, UIA-N \u3c 0.006 mg L-1) maintained high survival rates beyond 5 days pf indicating potential to successfully initiate exogenous feeding. Exposure to 1 mg L-1 TA-N (0.020 mg L-1 \u3c UIA-N \u3c 0.054 mg L-1) did not alter significantly survival with respect to control groups. Significant interactions between the spawn and the tolerance to hypoxia or elevated ammonia were detected in both experiments, indicating that variations among spawns need to be accounted for when determining safe levels for hatchery production. Statement of relevance Achieving a reliable supply of high quality eggs and larvae is one of the main challenges of the developing marine aquaculture industry. Most studies to date have focused on maternal determinants of egg quality but the viability of embryos and newly hatched larvae can be impacted after fertilization if environmental conditions become unfavorable due to intensive hatchery conditions; this topic is poorly documented in marine fishes to date. This study provides data on the effects of two major stressors acting under high density culture (hypoxia and elevated ammonia concentration) on embryos and newly hatched larvae of the red snapper; the results highlight the importance to consider variations among spawns/parents when determining safe levels for hatchery production and also the high sensitivity of red snapper to these stresses, suggesting that this topic should be investigated in other marine offshore species. Relevance of the research to commercial aquaculture. The research contributes to control egg quality. (C) 2016 Elsevier B.V. All rights reserved

A Histological Study of Gametogenesis In Captive Red Snapper \u3ci\u3eLutjanus campechanus\u3c/i\u3e

Gametogenesis was monitored histologically in wild-caught red snapper (Lutjanus campechanus, Poey) maintained in captivity under simulated natural photothermal conditions. Gonads were collected every 2–3 weeks (average n = 14) for histology during the pre-spawning season (February to May, temperature increasing from 16°C to 24°C). Primary vitellogenic oocytes were first observed in one female when temperature reached 20°C. Subsequent samples revealed females in pre-vitellogenesis or at early stages of vitellogenesis, although one female had tertiary vitellogenic (Vtg3) oocytes. The first histological signs of spermatogenesis were observed when temperature reached 17°C. Spermatozoa were observed in testicular lobules of all males sampled on 14 May (24°C) but little or no sperm was released during manual stripping. Ten males and 10 females were left in tanks and monitored for spawning. No egg release was observed during the monitoring period that encompassed the natural spawning season of wild red snapper. Ovarian biopsies taken during the late spawning season (16 July) revealed that four of eight sampled females had Vtg3 oocytes. Males were manually stripped but released no sperm. These results indicate that captive red snapper can complete gametogenesis in photothermal controlled systems. Additional research is needed to develop procedures that will achieve reliable maturation and spawning

Development of a Methodology for Intensive Larviculture of Atlantic Croakers

The Atlantic Croaker Micropogonias undulatus (Sciaenidae) is a candidate species for marine baitfish aquaculture in the southeastern United States because of its high value and common use as live bait by recreational fishers. However, an efficient larviculture procedure has not been reported to date; development of such a procedure was the impetus for this study. Embryos were obtained from captive broodstock that were induced to spawn volitionally by using a single injection of a luteinizing hormone releasing hormone agonist. Larvae were cultured at low density (initial density = 6.4 larvae/L) via intensive culture methods, including the use of recirculating filtration systems and of rotifers, brine shrimp Artemia spp., and micropellets as larval foods. The trial was performed in six 1,100-L tanks at a salinity of 14-29, with average rearing temperatures of 23.6 degrees C and 24.6 degrees C. At the completion of the study (39 d posthatch), mean SLs were 24.7mm (SE = 0.738) for larvae cultured at 24.6 degrees C and 23.0mm (SE = 0.624) for larvae cultured at 23.6 degrees C. Mean survival at 39 d posthatch was 25.9% and did not differ significantly between temperature groups. This work demonstrated a successful methodology for intensive larviculture of Atlantic Croakers and can serve as a platform for the experimentation that will be necessary to develop economically viable procedures for intensive production of this species. Received May 10, 2013; accepted August 24, 201

Atlantic croaker milt management in hatchery

The objective of this study was to optimize the methodology for spectrophotometric determination of sperm concentration in Atlantic croaker Micropogonias undulatus L. milt and to estimate its potential for short-term cold-storage. The spectrophotometric determination of sperm concentration was evaluated using milt samples from six males serially diluted in Hank's balanced salt solution at 200 mOsm kg 1 (HBSS). The predictive power of regression models between sperm concentration and absorbance was determined from 200 to 500 nm and found to be highest within the visible spectrum despite a peak of milt absorbance at 288 nm. Absorbance reading at 400 nm was selected for further analysis to maximize the absorbance of the sample hence the sensitivity of the method while minimizing the impact of potential sample contamination with blood. The standard-curve of correlation between sperm absorbance at 400 nm and concentration was validated and held an accuracy ranging between 7.40% and +4.56% across males. Total sperm motility duration and the proportion of motile spermatozoa were significantly higher in milt samples diluted 1:3 in HBSS than in the undiluted control during up to 30 h of cold-storage.The methodologies investigated in this study can be applied to optimize sperm usage and achieve predictable artificial fertilization protocols in Atlantic croaker