Emerging Aquaculture Species Research Articles

Embryonic and larval development of black jewfish, Protonibea diacanthus: A new candidate for aquaculture in northern Australia

Black jewfish Protonibea diacanthus is a large, commercially important fish distributed across the tropical Indo-Pacific. In Australia, there is an established commercial wild fishery for the species but it’s aquaculture potential has not been investigated. This research presents hatchery production of native P. diacanthus in Darwin, Australia and documents ontogeny of early life stages of this species over three trial runs. Wild P. diacanthus were induced to spawn with luteinizing hormone-releasing hormone analog (LHRHa) and eggs were released approximately 25–28 h after injection (0.88 ± 0.01 mm in diameter with oil globule 0.24 ± 0.01 mm). Larvae hatched 12 h after spawning. At one day post hatch (dph) larvae were 2.68 ± 0.01 mm standard length with 0.15 ± 0.01 mm oil globule diameter. Larvae mouths opened at 31 h post hatch (hph) and first feeding was seen at 57 hph. Swim bladder inflation (92 %) occurred between 40 and 62 hph. Larvae were progressively fed rotifers, Artemia and Otohime microdiet, and metamorphosis occurred between 20 and 25 dph, completing as they reached over 13 mm standard length. Tail biting cannibalism began with the onset of metamorphosis and caused significant mortality until approximately 24 dph when metamorphosed juveniles could be handled and moved to low stocking density systems. This study demonstrates that northern Australian P. diacanthus is amenable to hatchery production and provides important foundational knowledge for this emerging aquaculture species.

Three genome assemblies of Opsariichthys bidens from Yangzte River, Pearl River and Qiantang River basins

Opsariichthys bidens is an endemic minnow, mainly distributed in China as an emerging aquaculture species. In this study, O. bidens collected from Yangzte River (YR), Pearl River (PR) and Qiantang River (QR) basins were used for karyotypic study and genome sequencing. Using PacBio long reads and Hi-C data, we assembled high-quality O. bidens genomes of 852.41 Mb (YR), 843.11 Mb (PR) and 840.94 Mb (QR) with scaffold N50 lengths of 21.01 Mb, 23.62 Mb and 24.75 Mb, respectively, of which 90.39%, 95.67% and 99.01% were anchored to 37, 38 and 39 chromosomes, respectively. 26,556 (YR), 25,036 (PR) and 26,283 (QR) protein-coding genes were predicted, respectively. The karyotype of O. bidens from YR, PR and QR were 2 N = 74 (6 m + 6sm + 4st + 58t), 2 N = 76 (4 m + 6sm + 4st + 62t) and 2 N = 78 (4 m + 4sm + 4st + 66t), respectively. Collinearity analysis and telomere predictions indicated that the observed chromosomal evolution was driven by Robertsonian translocation. These genome assemblies facilitate cryptic species determination, evolutionary study and genetic breeding of genus Opsariichthys.

Isolation and identification of hybrid snakehead rhabdovirus (HSHRV) and its immune response in the hybrid Snakehead((male Channa argus × female Channa maculata)

Hybrid snakehead is an emerging aquaculture species obtained from the mating of Channa argus (♂) and Channa maculate (♀). It has the advantages of fast growth and strong disease resistance. Viral diseases caused by hybrid snakehead rhabdovirus (HSHRV) critically affect the hybrid snakehead industry. We isolated and identified a highly virulent strain of HSHRV from a naturally occurring hybrid snakehead, namely HSHRV-GZ22. It showed clinical signs of sinking, superficial blackening, spinning, acute internal congestion, and hemorrhage, along with blackening and enlargement of the liver, spleen, and kidneys. Histopathological analysis showed multiple tissue lesions in the liver, spleen, and kidneys, characterized mainly by massive inflammatory cell infiltration, interstitial hemorrhage, and partial cell necrosis. Pathogen analysis identified the virus as HSHRV. Immunofluorescence analysis (IFA) with HSHRV-specific antibodies confirmed the virus and electron microscopic observation showed that the bullet-like virus particles had a size of approximately 150 nm. The replication efficiency of HSHRV was 107.33 TCID50/mL. The glycoproteins of the isolates were cloned and sequenced, and a phylogenetic tree was constructed. The HSHRV-GZ22 isolates clustered into a single branch with the reported HSHRV-C1207, and it had a high degree of homology with Siniperca chuatsi rhabdovirus (SCRV). HSHRV-GZ22 was regressively infected, clinical and pathological symptoms were similar to naturally occurring fish, with a fatality rate of about 85 %. qRT-PCR was performed to determine the viral replication in different tissues of hybrid snakehead, and the viral copies were found to be highly expressed in the liver, spleen, kidney, and intestine. HSHRV-GZ22 activated the antiviral immune pathway in hybrid snakeheads during infection, and the expressions of IgM, IRF7, ISG12, and IFNγ were significantly altered. In this study, we isolated a strong virulent strain of HSHRV and characterized it; in addition, it provided insights into the pathogenesis of HSHRV and immune response in hybrid snakehead, while also advancing the methods for diagnosing and preventing diseases caused by HSHRV.

Sensory profiles and market potential of burbot Lota lota maculosa- An emerging aquaculture species

The aquaculture industry needs to increase the diversity of fish species to meet consumers' escalating demands. Burbot (Lota maculosa) has emerged as a promising candidate for such diversification. Nonetheless, a dearth of knowledge exists concerning their sensory characteristics and overall consumer acceptance. This study sought to investigate these crucial aspects, which are instrumental in assessing the market potential of this fish species. A consumer survey was conducted in Idaho from March through July 2017 to initially evaluate burbot's consumer acceptance and market potential. Results showed that over 96% of consumers liked the texture of burbot, 92% liked the flavor of the burbot, and 90% would try burbot again. Significant reasons for consumers' willingness to eat burbot included cooking preparation, tasty, mild flavor, excellent texture, and excellent flavor. Results from this indicate that burbot is a promising food fish candidate for commercialization. Based on these results, a follow-up panelists survey and sensory analysis were conducted in April 2019 to further investigate consumer acceptance and sensory properties of burbot when compared to other prominent aquaculture species (trout and tilapia). The three species exhibited different sensory profiles; however, burbot was ranked significantly higher for aroma, flavor, and taste. Conversely, panelists found tilapia and trout to be significantly (P < 0.05) firmer than burbot for firmness. The results from the sensory testing showed that 87% and 81% of panelists preferred burbot to tilapia and trout, respectively, and 79% would be willing to try this as a new species on the market. The distinct profiles of burbot indicate that this fish species would be highly marketable and if available would contribute to the diversification of U.S. commercial aquaculture by offering a delicate white fillet option to salmonids.

Filtration rate and bioremediatory potential of the tropical blacklip rock oyster Saccostrea lineage J

The tropical blacklip rock oyster Saccostrea lineage J is an emerging aquaculture species displaying fast growth rates, large sizes and resilience to fluctuations in temperature and salinity, all characteristics that suggest it would be well-suited to bioremediatory applications. To investigate their bioremediatory potential, the present study aimed to (1) determine the influence of temperature (20, 24, 28, 32°C) on the filtration rate of Saccostrea lineage J and (2) describe and quantify uptake in total nitrogen (TN), total phosphorus (TP), total suspended solids (TSS) and chlorophyll a (chl a), using prawn pond effluent and 2 levels of oyster stocking density. The results demonstrated that higher water temperatures promote a faster filtration rate and identified an optimal performance range of 24 to 32°C for a filtration rate of 12.68 to 15.20 l h-1 g-1. In addition, the highest density (0.66 oysters l-1) of stocked oysters resulted in significant reduction of all water quality parameters, with TN reduced by 13%, TP by 16%, TSS by 95% and chl a by 29% when compared to unstocked controls after 3 h. Tissue analysis of 10 oysters with a mean whole weight of 75.4 g revealed a mean of 0.09 g of nitrogen per oyster. Scaling these values suggests that 1.20 kg of nitrogen is removed per tonne of harvested oysters. This study is the first to investigate the bioremediatory potential of Saccostrea lineage J and demonstrates their potential to improve aquaculture wastewater treatment practices and bioremediation.

In Vitro Profiling of Potential Fish Probiotics, Enterococcus hirae Strains, Isolated from Jade Perch, and Safety Properties Assessed Using Whole Genome Sequencing.

The demands of intensified aquaculture production and escalating disease prevalence underscore the need for efficacious probiotic strategies to enhance fish health. This study focused on isolating and characterising potential probiotics from the gut microbiota of the emerging aquaculture species jade perch (Scortum barcoo). Eighty-seven lactic acid bacteria and 149 other bacteria were isolated from the digestive tract of five adult jade perch. The screening revealed that 24 Enterococcus hirae isolates inhibited the freshwater pathogens Aeromonas sobria and Streptococcus iniae. Co-incubating E. hirae with the host gut suspensions demonstrated a two- to five-fold increase in the size of growth inhibition zones compared to the results when using gut suspensions from tilapia (a non-host), indicating host-specificity. Genome analysis of the lead isolate, E. hirae R44, predicted the presence of antimicrobial compounds like enterolysin A, class II lanthipeptide, and terpenes, which underlay its antibacterial attributes. Isolate R44 exhibited desirable probiotic characteristics, including survival at pH values within the range of 3 to 12, bile tolerance, antioxidant activity, ampicillin sensitivity, and absence of transferable antimicrobial resistance genes and virulence factors commonly associated with hospital Enterococcus strains (IS16, hylEfm, and esp). This study offers a foundation for sourcing host-adapted probiotics from underexplored aquaculture species. Characterisation of novel probiotics like E. hirae R44 can expedite the development of disease mitigation strategies to support aquaculture intensification.

Improving green sea urchin (Strongylocentrotus droebachiensis) hatchery production by determining effective settlement cues and post-settlement conditions

Hatchery production methodologies of Northeastern U.S. green sea urchins (Strongylocentrotus droebachiensis) have yielded low settlement success and post-settlement survival (approximately 1–5%) contributing towards high costs for producing juveniles for this emerging aquaculture species. These are likely attributed to hatchery operations needing to optimize settlement cues and post-settlement food supplies. This study examined a range of potential settlement cues using adult conspecifics or a benthic diatom biofilm (Cylindrotheca closterium or Nitzschia sp.) alone, or in combination with seawater conditioned with conspecifics or macroalga (Saccharina latissima or Ulva lactuca). This study also examined whether sea urchin post-settlement survival and growth would improve using a benthic diatom food source (C. closterium or Nitzschia sp.) alone or in combination with an additional macroalga food source (S. latissima or U. lactuca). Both trials were conducted under hatchery ambient (control 12 °C) or elevated (14 °C) temperatures to determine whether temperature elevation could enhance S. droebachiensis settlement success and post-settlement growth. This study also examined what influence biofilm age (1, 4 and 8 weeks) and seawater salinity (26, 30, 33 and 36) had on settlement success to help towards optimizing hatchery methods. This study did not improve post-settlement survival causing it to remain a significant barrier in mass producing juveniles, but it did increase juvenile growth by 30–40% and reduce growth variability when fed the benthic diatom C. closterium in combination with U. lactuca. This combination also served as an adequate settlement cue for this species. The use of a conspecific influenced biofilm substantially improved settlement success from 1 to 5% to 50–80%. Seasonal timing and age (4 weeks) of this biofilm indicated importance in yielding this success which will be location specific. The use of conspecific biofilms for improving post-settlement survival requires further investigation and is worth examining in combination with C. closterium and U. lactuca towards enhancing S. droebachiensis production in the Northeastern U.S. Elevating seawater temperature by 2 °C had no significant effect on settlement, growth, or survival in this study. Salinities of 30–33 were optimal yielding 3–7 times more settlement compared to salinities 27 and 36. This study highlights that settlement trials need to incorporate post-settlement survival measurements for at least 1–2 months to truly reflect the effectiveness of method interventions and consider extending the time before turning seawater flow back on into settlement tanks from 24 to 48 h by up to 72–96 h to facilitate greater settlement success if seawater quality parameters permit it.

Utilizing ISSRseq genotyping to assist growth selection in tomato grouper (Cephalopholis sonnerati) without broodstock information

AbstractGrowth selection in fish is essential for aquaculture; however, long generation times and artificial breeding limitations present challenges for breeding endeavors. The tomato grouper (Cephalopholis sonnerati) is an emerging aquaculture species with a generation cycle of at least 5 to 10 years. Mixed culture of broodstocks and natural mating are commonly employed in hatcheries. To expedite the selection process for tomato grouper, we utilized ISSRseq technology for assisted future growth selection. After 6 months of rearing, we selected 48 individuals, including 24 fast‐growing and 24 slow‐growing individuals (representing the top and bottom 10% of samples). These samples produced 932 SNPs. Although specific broodstock pairing information is unavailable, our results suggest that these fry likely originated from multiple broodstock exhibiting considerable diversity. Further analysis of genetic relationships among individuals revealed three main clades. One clade contained a higher proportion of faster‐growing individuals (80%), while another featured a lower proportion of rapidly growing individuals (28.6%). Through the relatedness network and further exclusion of individuals, the faster‐growth clade comprised 92.3% of fast‐growing individuals. The faster‐growth clade is appropriate for further development into a high‐growth strain. Our findings demonstrate that molecular markers can advance population selective breeding to family selection in aquaculture breeding research.

Spawning induction for Latin American fishes

AbstractAquaculture offers solutions to meet the growing global demand for fish, and reports from the UN‐FAO indicate that aquaculture production in Latin America (LA) has grown at rates above the world average in recent years. One of the major constraints in the diversification of LA aquaculture is the control of reproduction in several popular native fish species for which difficulties in captive propagation have not yet been sufficiently overcome. This article reviews the use of hormone treatments to promote reproduction in females of these native fish species. LA has played a key role in the history of development of hormone administration, including the first hormonally induced spawning. That contribution is included in a historical overview of the discovery of the major hormones used in fish culture. The review provides a summary of difficulties to propagate females of various native fishes and the effects of administering hormones to enhance reproduction. Induced spawning of certain freshwater species was mainly achieved with pituitary extracts or human chorionic gonadotropin (hCG), although gonadotropin‐releasing hormone analogues (GnRHa) treatments are being researched, and successful studies suggest that low doses may be more effective. Research on new and emerging aquaculture species has applied both gonadotropins (Gths) and GnRHa‐based treatments, and GnRHa treatments have shown potential for marine species. However, native marine species new to aquaculture have also been conditioned to spawn spontaneously without hormones. Finally, we proposed future lines of research to examine reproductive strategies and GnRHa‐based hormone treatments to improve reproductive control for economically important fish species of LA.

Thermal physiology of tropical rock lobster (Panulirus ornatus); defining physiological constraints to high temperature tolerance

This study investigated the effect of chronic temperature acclimation (24, 26, 28, 30, and 32 °C) on growth, aerobic metabolism, feeding, and gut evacuation rate of early juvenile spiny lobster, Panulirus ornatus (initial weight = 0.48 ± 0. 03 g) to determine thermal optima for growth and identify physiological constraints at high temperatures for this emerging aquaculture species. Groups of 7 juvenile lobsters were communally cultured (n = 4) for 45 days post-acclimation and solely fed on a formulated feed. Lobster specific growth rate (SGR), apparent feed intake (AFI), and specific feed consumption (SFC) displayed unimodal response to temperature peaking at 28.0, 27.9, and 26.2 °C, respectively. Similarly, survival had a significant quadratic relationship with temperature; however, it displayed an inverse relationship to SGR, AFI, and SFC where the lowest survival was found at 29.1 °C. Continuous exponential increases in lobster standard, routine and maximum metabolic rates, and aerobic scope were observed up to a maximum non-lethal temperature of 32 °C. Gastrointestinal evacuation rate (GIER) (>96%) increased minimally between 24 and 30 °C from 2.5 h to 2.9 h and substantially rose to 5.1 h at 32 °C. While the feed conversion ratio improved with increasing temperature, the temperature optimum for metabolic feeding efficiency closely matched specific growth rate and apparent feed intake. These findings show that optimum temperature for growth performance of juvenile P. ornatus does not align with maximum aerobic scope, rather growth was limited by prolonged GIER (up to 5.1 h) at high temperatures 32 °C which constrained food consumption. These findings contribute to the growing body of literature debating the universality of aerobic scope to define physiological thermal boundaries of aquatic ectotherms suggesting thermal performance of lobsters under sub-lethal temperatures to be regulated by feed intake and driven by digestive processes such as GIER. Future research should focus on lobster feed formulation and its influence on digestive processes such as GIER, foregut evacuation, and digestibility which may influence the thermal tolerance of spiny lobsters in culture.

Production of a monoclonal antibody specific to sablefish (Anoplopoma fimbria) IgM and its application in ELISA, western blotting, and immunofluorescent staining

Sablefish (Anoplopoma fimbria) are an emerging aquaculture species native to the continental shelf of the northern Pacific Ocean. There is limited information on both innate and adaptive immunity for this species and new tools are needed to determine antibody response following vaccination or disease outbreaks. In this paper, a monoclonal antibody, UI-25A, specific to sablefish IgM was produced in mice. Western blotting confirmed UI-25A recognizes the heavy chain of IgM and does not cross react to proteins or carbohydrates in serum of four other teleost species. An ELISA was developed to measure Aeromonas salmonicida specific IgM in the plasma of sablefish from a previous experiment where fish were immunized with a proprietary A. salmonicida vaccine. UI-25A was used in Western blot analyses to identify immunogenic regions of A. salmonicida recognized by this specific IgM from vaccinated sablefish. Immunofluorescent staining also demonstrated the ability of UI-25A to recognize membrane-bound IgM and identify IgM + cells in the head kidney. These results demonstrate the usefulness of UI-25A as a tool to improve the understanding of antibody-mediated immunity in sablefish as well as to provide valuable information for vaccine development and expansion of aquaculture efforts for this fish species.

Improving the weaning of larval giant kōkopu, Galaxias argenteus: An emerging aquaculture species

AbstractUsing live feed in fish larviculture is more expensive and challenging than formulated feeds, incentivizing the early weaning of larvae. In New Zealand, the aquaculture of larval giant kōkopu, Galaxias argenteus, is being commercialized because of its high value and to supplement the wild fishery. As an emerging aquaculture species, inefficiencies remain in the production process, inhibiting financial viability. This study reports on the ability of these larvae to consume formulated larval diets across four ages (18, 21, 25, and 28 days after hatching, DAH) at each of the three daily feeding events (Morning, Midday, and Afternoon) during commercial production. At 18 DAH, little to no formulated feed was consumed at either of the three feeding events throughout the day. At 21 DAH, mean gut fullness increased and the number of fish with empty stomachs reduced by the end of the Morning and Afternoon feeding events. Both variables improved further for larvae at 25 and 28 DAH. Formulated feed consumption did not differ between larvae aged 25 and 28 DAH indicating that 3 days of feeding live feed could be removed from the feed regime. This change would save 13% on the cost of live feed; however, further research is required to determine the potential impacts on growth and survival.

Dietary supplementation of astaxanthin modulates skin color and liver antioxidant status of giant grouper (Epinephelus lanceolatus)

Giant grouper (Epinephelus lanceolatus) is an emerging aquaculture species in Southeast Asia and Australia with limited knowledge of its nutrient requirements and effects of supplements on its physiology. The present study investigated the effects of astaxanthin, vitamin E, and combinations on growth performance, body coloration, and the antioxidant status of juvenile giant grouper. Nine isonitrogenous (crude protein = 65 % ± 0.7 %) and isolipidic (crude lipid = 10 % ± 0.3 %) diets were formulated using a 3 × 3 factorial design, including three levels astaxanthin (0, 75, and 150 mg/kg) and vitamin E (0, 250, and 500 mg/kg), respectively. Each of the nine diets was fed to triplicate groups of 15 giant grouper (18.04 ± 0.92 g) for 30 days. Giant grouper fed the different diets exhibited no significant differences (p > 0.05) in specific growth rate (4.87 %/day - 5.21 %/day). However, dietary astaxanthin supplementation significantly enhanced the redness (a*), yellowness (b*b*), chroma, and hue values of the fin, regardless of the dose supplemented. Giant grouper fed astaxanthin at 75 and 150 mg/kg diet were more yellow and had three times higher b* values than fish fed non-supplemented diets. Further, total antioxidant capacity (TAC; mmol Trolox equivalent) in liver tissues was significantly increased in fish fed any of the astaxanthin-supplemented diets (p ≤ 0.05). In contrast, TAC levels were not affected by vitamin E supplementation. Malondialdehyde (MDA) levels were not significantly (p > 0.05) affected by astaxanthin or vitamin E. Findings from this study will contribute toward a better understanding of the dietary effects of antioxidant and pigment in juvenile giant grouper. We present that dietary treatment can modulate giant grouper pigmentation and may be used in the live fish trade. Further, this study contributes to narrowing the knowledge gap in formulating appropriate diets for giant grouper, which to date is fed diets formulated for other species.

Effects of Salinity on the Growth, Physiological Characteristics, and Intestinal Microbiota of the Echiura Worm (Urechis unicinctus)

Intertidal biota is subjected to significant fluctuations in salinity. Urechis unicinctus, a typical species thriving in intertidal sediments, have relatively simple anatomy structure and therefore could be considered as an ideal species for salinity acclimation. Moreover, due to the high nutrients, U. unicinctus has become an emerging aquaculture species in China. In this study, we investigated the effects of salinity on the growth performance, coelomic fluid biochemical indices, antioxidant enzyme system, Na+/K+-ATPase, and non-specific immune enzyme activities, as well as intestinal microbiota composition of this species in an 8-week experiment. The results indicated U. unicinctus is a euryhaline species that can tolerate salinities from 15‰ to 40‰ and demonstrated the highest growth performance at 30‰. Physiological characteristic analyses of coelomic fluid and intestines indicated that the salinity range of 15‰ to 30‰ is more suitable, while 10‰ and 40‰ salinity ranges seem unsuitable for juvenile U. unicinctus. Furthermore, intestinal microbiota analysis indicated salinity had a significant effect on the composition structure. KEGG pathway analysis indicated that antioxidant related metabolic pathways and amino acid metabolic pathways may play important roles in gut microbiota under salinity stress. Comprehensive analysis of intestinal bacteria and enzyme activities indicated Unidentified Rhodobacteraceae, Vibrio, and Shimia may play important roles in high salinity acclimation, while Legionellaceae may act as important microbiota in low salinity acclimation. Moreover, Ruminococcus, Oscillospira, Lachnospiraceae, Clostridiales, and S24-7 showed negative correlations with the antioxidant and nonspecific immune enzymes, indicating that these bacteria can be considered as important candidates of probiotics for U. unicinctus aquaculture industry. The findings of this study will extend our understanding of the effects of salinity on the growth and health of U. unicinctus and contribute to a better understanding of the salinity acclimation strategies of organisms in intertidal zones.

Polarity affects the antioxidant and antimicrobial activities of jellyfish (Acromitus hardenbergi) extracts

Jellyfish is an emerging aquaculture species, farmed for Oriental cuisines and nutraceutical ingredients. This study aimed to examine antioxidative and antimicrobial potentials of various fractions of the jellyfish, Acromitus hardenbergi. The bell and oral arms of the jellyfish were sequentially extracted with petroleum ether (PE), dichloromethane (DCM), chloroform (CHCl3), methanol (MeOH), and water (H2O) to extract its bioactive in an increasing polarity gradient. Test fractions were assayed for antiradical activities using electron spin resonance spectrometry, β-carotene-linoleate model and Folin-Ciocalteu assay; and antimicrobial activity against 2 Gram-negative bacteria, 4 Gram-positive bacteria and 2 fungal species using the disc diffusion assay. All fractions were also subjected to Fourier Transform Infrared (FTIR) analysis to identify types of functional groups present. It was found that the hydrophilic extracts (H2O fractions) possessed the most effective radical scavenging activity (p &lt; 0.05) while the lipophilic extracts (PE fractions) the most active antimicrobial activity, especially against Gram-positive bacteria (p &lt; 0.05). Total oxidation substrates content was found to be highest in the PE fractions of jellyfish bell and oral arms (p &lt; 0.05). FTIR data showed that the H2O and MeOH fractions contains similar functional groups including -OH, -C=O, -N-H and -S=O groups, while the PE, DCM, and CHCl3 fractions, the -CH3, -COOH groups. This study showed that A. hardenbergi contains antioxidants and antimicrobials, thereby supporting the traditional claim of the jellyfish as an anti-aging and health-promoting functional food. Bioassay-guided fractionation approach serves as a critical milestone for the strategic screening, purification, and elucidation of therapeutically significant actives from jellyfish.

The isosmotic point as critical salinity limit for growth and osmoregulation, but not survival, in the wolf eel Anarrhichthys ocellatus.

Members of wolf fish family Anarhichadidae have emerged as potential cold-water marine aquaculture species. This study examined growth performance and osmoregulation in juvenile wolf eel (Anarrhichthys ocellatus) held in a series of dilute salinities (30, 14, 9, and 6 ‰) over an 8-week trial. At the conclusion of the growth study, fish were sampled for analysis of gill and intestine enzyme activity, plasma ion content, and muscle moisture. Growth rate remained positive in all salinities throughout the 8-week trial. Specific growth rate was maintained above 3.0% mass day-1 at salinities of 30 and 14 ‰, but was significantly reduced at 9 (2.9% mass day-1) and 6 ‰ (2.0% mass day-1). Muscle water content increased with increasing salinity dilution (77.9% water in 30 ‰; 79.8% water in 6 ‰), and plasma osmolality (~ 320mOsmkg-1) was maintained in salinities as dilute as 9 ‰ but was significantly lower (~ 280mOsmkg-1) in the most dilute salinity of 6 ‰. Segmental linear regression analyses revealed that the calculated isosmotic point for wolf eel of ~ 10.6 ‰ was a critical limit for maintaining growth performance and osmoregulatory homeostasis. It is an important finding that fish considered to be a typical marine stenohaline organism could maintain ion and water balance as low as the isosmotic point, and exhibit survival and positive growth rates in salinities as dilute as 6 ‰. This work delivers a fundamental step in the empirical examination of this emerging aquaculture species and provides a model for evaluating osmoregulatory performance of marine stenohaline fishes in low-salinity aquaculture.

Life cycle assessment of tiger puffer (Takifugu rubripes) farming: A case study in Dalian, China

In China, energy consumption and carbon emission by the aquaculture industry have become major problems. The tiger puffer (Takifugu rubripes) is an emerging aquaculture species in China, but its environmental impact during the farming process has not yet been evaluated systematically. To the best of our knowledge, this is the first life cycle assessment (LCA) of tiger puffer land-sea relay strategy in Dalian, China. To analyze the environmental impact of the tiger puffer farming process, the following four stages were considered: seed rearing, deep-sea cage farming-1, industrial recirculating aquaculture, and deep-sea cage farming-2. The LCA software GaBi 10.5 academy version and CML-IA-Jan. 2016-world method were used to calculate the environmental impacts. According to the LCA results, marine aquatic ecotoxicity potential was the largest contributor to the environmental impact, and industrial recirculating aquaculture was the largest farming stage in the whole tiger puffer farming process. Energy in the form of electricity, coal, and gasoline was consumed to maintain the power supply in the tiger puffer farming process, and it was a key factor that influenced the environmental performance. Based on the sensitivity and energy analyses, energy consumption for equipment operation at the industrial recirculating aquaculture stage, feed consumption, and gasoline consumption for transportation at the deep-sea cage farming-2 stage need to be carefully considered. The following improvement measures were suggested to improve the environmental performance of tiger puffer farming and the aquaculture industry: establish electricity, wind power, and solar energy integrated management systems; ex-ante LCA for parameter optimization in future technology research and development; and new production strategies such as aquaponics and integrated multi-trophic aquaculture. Moreover, life cycle inventory (LCI) of tiger puffer land-sea relay farming was established to obtain essential information, enrich aquaculture LCI databases, and support aquaculture LCA research.

Thermal tolerance, metabolic scope and performance of meagre, Argyrosomus regius, reared under high water temperatures.

This article reports on the thermal tolerance, metabolic capacity and performance of juvenile meagre (Argyrosomus regius) reared under three high water temperatures (24, 29 and 34°C) for three months. The analysis includes the thermal effects on the growth performance, metabolism and physiology of meagre, including a range of molecular, haematological, metabolic, enzymatic and hormonal indicators, as well as the effects on the proximate composition and ingestion speed. Meagre performs best between 24 and 29°C while the temperature of 34°C is very close to the upper end of its temperature tolerance range. At 34°C meagre exhibits a poor growth performance and physiological status, increased blood clotting, high mortality rates and a diminished capacity for aerobic metabolism, as indicated by its low aerobic scope (129mgkg-1 h-1). Meagre may tolerate short exposures to high temperatures after sufficient acclimation (Critical thermal maximum of 37.5°C after acclimation to 29°C) but its overall performance declines under prolonged exposure, suggesting that this emerging aquaculture species may be vulnerable to global warming. Our work corroborates previous findings on the thermal preferences of the species, identifies critical biological thresholds, and provides insights into the effects of prolonged exposure to high temperature regimes.

Cross-species Exon Capture and Whole Exome Sequencing: Application, Utility and Challenges for Genomic Resource Development in Non-model Species.

Comprehending the genetic architecture of complex traits has many applications in evolution, ecology, conservation biology and plant and animal production systems. Underlying research questions in these fields are diverse species that often have limited genetic information available. In aquaculture, for example, genetic progress has been slow in many species due to a lack in such genetic information. In this study, zebrafish (as a well-studied model species) was used in cross-species transfer to develop genomic resources and identify candidate genes underling growth differentials in dusky kob. Dusky kob is a Sciaenid finfish and an emerging aquaculture species. The zebrafish All Exon Predesigned Probe-set capture protocol was used to enrich fractionated DNA samples from kob, classified as either large or small, before massive parallel sequencing on the Ion Torrent platform. Although vast quantities of sequence data were generated, only about 30% of contigs could be identified as zebrafish homologues. There were numerous species-specific sequences and inconsistent coverage of sequencing products across samples, likely due to non-specific binding of the probe-set as a result of the evolutionary divergence between zebrafish and kob. Nonetheless, more than 55,000 SNPs could be reliably identified and genotyped to the individual level. Using SNP genotypic divergence estimates, between large and small cohorts, a number of candidate genes associated with growth was also identified for future investigation. These findings contribute to the growing body of evidence demonstrating the utility ofa cross-species capture approach in the development of important genomic resources for understanding traits of interest in species without reference genomes.

Bacterial microbiome of dusky kob Argyrosomus japonicus eggs and rearing water and the bacteriostatic effect of selected disinfectants

The dusky kob Argyrosomus japonicus is an emerging aquaculture species in South Africa. To support industry growth, existing hatcheries frequently sell or donate excess eggs to neighbouring farms, raising concern over the potential transfer of infectious disease agents. Chemical disinfectants are frequently used to prevent transmission of diseases, but their application has shown large variations between finfish species and very little is known about the efficacy and impact of disinfectants on dusky kob eggs or larvae. A thorough understanding of the bacterial communities associated with specific fish species can inform the need for specific chemical agents and guide a more targeted approach for disease control and treatment. Therefore, this study used next generation sequencing (NGS, 16S rDNA gene) and downstream bioinformatics analysis to describe the bacterial microbiome associated with the eggs and rearing water of dusky kob. Four chemical disinfectants [chloramine-T (C-T), povo‑iodine (PI), hydrogen peroxide (H2O2) & formaldehyde (CH2O)], applied at different concentrations and times, were then tested for their ability to disinfect eggs and seawater. The impact of each disinfectant on early larval development was also assessed. A total of 11,605 individual bacterial operational transcriptional units (OTUs) were identified from the dusky kob egg (7352 OTUs) and hatchery water (4253 OTUs) samples. Non-metric multidimensional scaling (NMDS) analysis revealed distinct differences in the composition of the microbiota associated with the egg and seawater samples. A moderate level of bacterial diversity was observed in all samples, with the seawater samples dominated by Rhodobacteraceae (65%) and Flavobacteriaceae (14%); whereas egg samples were dominated by Pseudoalteromonadaceae (49%), Vibrionaceae (27%) and Colwelliaceae (8%). A classical univariate statistical comparison identified 6 differentially abundant OTUs at phylum level, 12 at family level and 19 at genus level; with members of the family Vibrionaceae found to be significantly (P = 0.0011) more abundant on dusky kob eggs samples. All tested chemical disinfectants were capable of reducing the bacterial load in seawater in a dose dependent manner, with the number of culturable bacteria on eggs decreasing significantly following exposure to PI and CH2O for five minutes (43% and 88% reduction in CFUs, respectively), compared with C-T and H2O2 (3% & 10%). Similarly, PI and CH2O significantly decreased the culturability of Vibrio species on eggs (79% & 75%), compared with C-T and H2O2 (12% & 14%). None of the disinfectants appeared to have any adverse impact on larval growth and morphology.