Blood Analyte Changes of Wild-Caught Adult Almaco Jack in Response to Acclimation to Recirculating Aquaculture Systems and Hyposalinity Treatment

Despite the utility of blood analyte evaluation as a diagnostic tool to assist in monitoring the health of marine fishes, baseline data are often lacking for many commercially important finfish species. The objective of this study was to compare hematology and plasma chemistry data for adult wild-caught Almaco Jack Seriola rivoliana at time of capture and again following a period of acclimation to a recirculating aquaculture system and hyposalinity treatment. A total of 30 clinically healthy adult fish were caught via hook and line in the eastern Gulf of Mexico, approximately 120 mi offshore from Madeira Beach, Florida. Blood was collected from a subset of these fish (n = 13) immediately after capture and again at 16 weeks postcapture from another subset (n = 12) following a 45-d antiparasitic hyposalinity treatment. A 19% increase in fish body weight was observed during the study period (16 weeks) and no overt health issues or mortality were noted. Compared to fish that were sampled immediately following capture, several significant differences (P < 0.05) were observed. Absolute white blood cells were lower in captive held fish, suggesting biological variation, antigenic stimulation in wild fish, and/or immunosuppression associated with stress in captive held fish. Lower sodium, chloride, and calculated osmolality indicate osmoregulatory adjustments following the hyposalinity treatment by 16 weeks postcapture. Other observed plasma biochemical differences presumptively reflect dietary and/or environmental changes, or physiological variation following acclimation to captive culture conditions. This study reports baseline blood analyte data of wild-caught Almaco Jack and documents hematological and plasma biochemical responses to their new environment as captive broodstock. Baseline hematological and plasma biochemistry data obtained during this study are the first reported for this species.

Shifts in the Skin-Associated Microbiota of Hatchery-Reared Common Snook Centropomus undecimalis During Acclimation to the Wild

The skin-associated microbiota of fish competes against pathogens for space and nutrients, preventing colonization by harmful bacteria encountered during environmental transitions such as those faced during stock enhancement. Thus, alterations in bacterial community structure during release of cultured fish have important implications for health of these individuals. This study investigated microbiota structure during acclimation of juvenile hatchery-reared common snook Centropomus undecimalis to the wild by comparing skin-associated microflora among snook in captivity, after 48 h of acclimation at release sites, and from the wild. After two days of acclimation, the microbiota of hatchery-reared snook mirrored that observed on wild snook. Relative abundances of potential pathogens were higher in captive fish, whereas acclimated and wild fish harbored bacterial taxa influenced by geographical factors and water quality at release sites. Predicted microbiota function of acclimated and wild fish showed higher production of protective amino acids and antimicrobials, identifying a mechanism for microbial supplementation of the immune defense of these fish. The two-day transition to wild-type microbiota suggests a temporal scale of hours associated with bacterial succession indicating that the microbiota, whose structure is vital to fish health, aids in acclimation of fish to new environments during stock enhancement efforts.

Benefits of a Bacillus probiotic to larval fish survival and transport stress resistance

The need for sustainable bacterial management approaches in aquaculture is crucial for advancement of the industry. Probiotics are a promising strategy as evidenced by benefits demonstrated in intensive larviculture of various marine fish species. In this study we investigate the effects of a mixed Bacillus species (B. licheniformis and B. amyloliquefaciens) probiotic on rearing of larval common snook (Centropomus undecimalis). Experimental treatments included (1) probiotics supplemented to the water and live feed, (2) probiotics supplemented to the water only, and (3) no probiotic controls. Data from two separate trials indicated up to 2.5 times higher survival with probiotic addition, as well as 20% higher survival 7 days following a transport event. These benefits were not explained by faster growth, measured water quality parameters, or innate immune enzyme activities. Microbiota analysis indicated the importance of system stabilization prior to larval stocking to improve rearing success and probiotic performance. ied Potential probiotic benefits include accelerated gastrointestinal tract development, enhanced immunity, inhibition of opportunistic bacteria, and improvements to water quality parameters. Results suggest this probiotic should be tested in other marine fish species in order to reduce larval rearing bottlenecks.

Health Characteristics and Blood Bacterial Assemblages of Healthy Captive Red Drum: Implications for Aquaculture and Fish Health Management

The newly emerging tissue microbiota hypothesis suggests that bacteria found in blood and tissues play a role in host health, as these bacterial communities have been associated with various noncommunicable diseases such as obesity, liver disease, and cardiovascular disease. Numerous reports have identified bacteria in the blood of healthy finfish, indicating bacteremia may not always indicate disease. Current research priorities in aquaculture include the development of technologies and practices that will allow for an effective reduction in antibiotic use for the prevention and treatment of disease. Overall, a better understanding of fish health is needed, particularly among species selected for commercial-scale production. This study investigated blood characteristics of cultured Red Drum Sciaenops ocellatus with the tissue microbiota hypothesis in mind. Bacterial assemblages within the blood were characterized using next-generation sequencing and compared with other various blood characteristics, including innate immune function enzymes, between two fish cohorts reared in aquaculture. A total of 137 prokaryotic operational taxonomic units (OTUs) were identified from the blood of Red Drum. Microbiota diversity and structure varied greatly among individuals, for which the number of OTUs ranged from 4 to 58; however, predicted metagenomic function was highly similar between individuals and was dominated by the metabolism of carbohydrates and amino acids and membrane transport. Communities were dominated by Proteobacteria, followed by Bacteroidetes, Firmicutes, and Actinobacteria. The most commonly identified genera included Acinetobacter, Bacillus, Corynebacterium, and Pseudomonas. Three genera previously identified as containing marine fish pathogens were detected: Corynebacterium, Pantoea, and Chryseobacterium. A subset of bacterial OTUs were positively correlated with superoxide dismutase activity and negatively correlated with lysozyme activity, indicating a relationship between blood microbiota and the innate immune system. The results of this study provide further evidence for the tissue microbiota hypothesis and demonstrate the potential for these bacterial communities to be linked to immunological characteristics often used as biomarkers for fish health.

Influence of tidal cycles on the endocrine control of reproductive activity in common snook (Centropomus undecimalis)

The aim of our study was to confirm the role of tidal pattern on the coordination of oocyte maturation and spawning in common snook Centropomus undecimalis. To do so, we studied oocyte maturation during the spawning season in relation to the tidal pattern in both males and females by means of histology and hormonal profiling along the pituitary-gonadal axis. Plasma LH levels, as well as transcript levels of gonadotropin genes (fshβ and lhβ) from the pituitaries of sexually mature male and female common snook were analyzed using a heterologous ELISA and quantitative RT-PCR, respectively. The fshβ and lhβ cDNAs were isolated and phylogenetic analysis of the deduced amino acid sequences revealed strong identity with other teleosts (75-90%). A strong link was found between tide and follicular development irrespective of the time of the day: female snook sampled on the rising tide were all found to have oocytes in the Secondary Growth Stage whereas females sampled at high tide or on the falling tide had oocytes in the later stages of maturation and ovulation. In addition, LH plasma and mRNA levels of fshβ and lhβ increased during the later stages of vitellogenesis peaking at ovulation in females. Plasma estradiol and testosterone significantly increased in late vitellogenesis (Secondary Growth Stage) and oocyte maturation (Eccentric Germinal Vesicle Step) respectively. Among male common snook sampled, no correlation was identified between tide and gonadal development. In addition, lhβ mRNA expression in males peaked at the mid germinal epithelium stage as for testosterone and 11-KT in the blood while fshβ expression and plasma LH levels peaked at late germinal epithelium stage. This study confirms the role played by tidal cycle on the entrainment of the later stages of oogenesis of common snook and provides a better understanding of the link between environmental and endocrine control of reproduction in this species.