The emerging orbicular batfish (Platax orbicularis) aquaculture is the most important fish aquaculture industry in French Polynesia. However, bacterial infections are causing severe mortality episodes. Therefore, there is an urgent need to find an effective management solution. Besides the supplying difficulty and high costs of veterinary drugs in French Polynesia, batfish aquaculture takes place close to the coral reef, where use of synthetic persistent drugs should be restricted. Medicinal plants and bioactive algae are emerging as a cheaper and more sustainable alternative to chemical drugs. We have studied the effect of local Polynesian plants and the local opportunistic algae Asparagopsis taxiformis on batfish when orally administered. Weight gain and expression of two immune-related genes (lysozyme g - Lys G and transforming growth factor beta - TGF-β1) were studied to analyze immunostimulant activity of plants on P. orbicularis. Results showed that several plants increased Lys G and TGF-β1 expression on orbicular batfish after 2 and 3 weeks of oral administration. A. taxiformis was the plant displaying the most promising results, promoting a weight gain of 24% after 3 weeks of oral administration and significantly increasing the relative amount of both Lys G and TGF-β1 transcripts in kidney and spleen of P. orbicularis.

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a b s t r a c tThe 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 concentrations were 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 (N 85% 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 b 0.26 mg L −1 , UIA-N b 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 b UIA-N b 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 relevanceAchieving 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 conside...

Arctic char, Salvelinus alpinus L. is a promising candidate for aquaculture expansion in Northern Europe, Canada, and the United States because of its excellent growth at low temperature, tolerance to high rearing density, high fillet yield, and superior flesh texture and flavor. To support this industry, several breeding programs in these regions currently focus on selection for growth and delayed maturation. While the growth potential of existing strains has been improved, preharvest sexual maturation remains a problem in this industry. This article describes current knowledge on the control of preharvest maturation in Arctic char at the hatchery level through the production of single‐sex and triploid populations and during the grow‐out phase through the manipulation of photoperiod and feed intake. Research perspectives on the subject are also suggested in order to complement the efforts of ongoing breeding programs.

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.

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 À1 (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 À7.40% 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.

The cultivated Eastern oyster (Crassostrea virginica) is sold in a niche market seeking rounder and thicker oysters. While most of the research conducted on optimal rearing densities focuses on survival and length growth, the present study looks at the oyster's shape. Three initial length classes were used for this study and reared in floating bags at different densities. The effects of the tested rearing densities were more pronounced on oyster shape than on length growth. In the smaller oysters, the three lower densities produced the rounder shape while thicker ones were obtained with the 500 densities. For the medium oysters, rounder and thicker shape was obtained with the two lower densities. The shape of the larger oysters was not influenced by the tested densities. This study showed that there was significant impact of rearing densities on smaller and medium oysters’ growth and shape, while only length growth of larger ones was impacted by this factor. Based on these findings, oyster farmers should target rearing density of 500 oysters per bag for the 20–35 mm stage, 250 oysters for the 35–50 mm oysters and 200 oysters for the larger ones (50–65 mm). The latest recommendations are based on technical considerations.

Background Ephippidae fish are characterized by a discoid shape with a very small visceral cavity. Among them Platax orbicularis has a high economic potential due to its flesh quality and flesh to carcass ratio. Nonetheless, the development of its aquaculture is limited by high mortality rates, especially due to Tenacibaculum maritimum infection, occurring one to three weeks after the transfer of fishes from bio-secure land-based aquaculture system to the lagoon cages for growth. Among the lines of defense against this microbial infection, the gastrointestinal tract (GIT) is less studied. The knowledge about the morphofunctional anatomy of this organ in P. orbicularis is still scarce. Therefore, the aims of this study are to characterize the GIT in non-infected P. orbicularis juveniles to then investigate the impact of T. maritimum on this multifunctional organ. Methods In the first place, the morpho-anatomy of the GIT in non-infected individuals was characterized using various histological techniques. Then, infected individuals, experimentally challenged by T. maritimum were analysed and compared to the previously established GIT reference. Results The overlapped shape of the GIT of P. orbicularis is probably due to its constrained compaction in a narrow visceral cavity. Firstly, the GIT was divided into 10 sections, from the esophagus to the rectum. For each section, the structure of the walls was characterized, with a focus on mucus secretions and the presence of the Na+/K+ ATPase pump. An identification key allowing the characterization of the GIT sections using in toto histology is given. Secondly, individuals challenged with T. maritimum exhibited differences in mucus type and proportion and, modifications in the mucosal and muscle layers. These changes could induce an imbalance in the trade-off between the GIT functions which may be in favour of protection and immunity to the disadvantage of nutrition capacities.