Sea Cages Research Articles

Evaluation of the protective efficiency of an autogenous Vibrio anguillarum vaccine in lumpfish (Cyclopterus lumpus) under controlled and field conditions in Atlantic Canada

Lumpfish (Cyclopterus lumpus) have become the predominant cleaner fish species used in North American salmon aquaculture. Vibrio anguillarum is a frequent pathogen of lumpfish in Atlantic Canada, and current vaccines against local isolates conferred low to moderate efficacy. This study evaluated the safety and efficiency of a V. anguillarum autogenous vaccine under controlled and field conditions. Two safety trials were conducted following the Canadian Food Inspection Agency (CFIA) regulations before field trial testing. The first safety trial was a common garden assay, and 250 PIT-tsgged lumpfish were used for five treatments per tank (PBS-negative control, Lab vaccine-positive control, autogenous intraperitoneal (IP) vaccine, autogenous dip vaccine, autogenous dip-IP boosted vaccine) in triplicates. Weight, gross pathology, and IgM titers were evaluated to determine the vaccine’s safety. After 10 weeks post-vaccination (wpv), lumpfish were bath-challenged with a lethal dose (1.24 x 106 CFU/mL) of V. anguillarum serotype O2. Survival rate, IgM titers, memory immune response, and cross-immune protection were evaluated. The second safety trial was conducted using a double vaccine dose in two groups, PBS and autogenous IP. The gross pathology score indicated a normal immune response without tissue damage, and no mortality nor fish health issues were observed in the immunized animals. The IP route of administration conferred the highest protection against the V. anguillarum challenge. The autogenous vaccine conferred long-term immunity but did not confer cross-protection against V. anguillarum serotype O1. To evaluate the efficiency of the autogenous vaccine under field conditions, 58,976 naïve lumpfish (8-10 g) were IP immunized with either the autogenous vaccine or the commercial Forte micro IV vaccine. After 7 wpv, the lumpfish were equally distributed into eight sea cages and co-cultivated with Atlantic salmon smolts (60,000 per cage). Lumpfish IgM titers, tissue bacterial loads, mortality, and sea lice count on salmon were monitored. The autogenous vaccine and Forte vaccine confer acceptable protection to the lumpfish in sea cages. No significant difference was observed between lumpfish vaccinated with autogenous and commercial vaccines under field conditions.

An Atypical Course of Cardiomyopathy Syndrome (CMS) in Farmed Atlantic Salmon (Salmo salar) Fed a Clinical Nutrition Diet.

Cardiomyopathy syndrome (CMS) poses a significant threat to farmed Atlantic salmon (Salmo salar), leading to high mortality rates during the seawater phase. Given that controlled experimental challenge trials with PMCV do not reproduce the mortality observed in severe field outbreaks of CMS, field trials on natural CMS outbreaks are warranted. This field study explored the impact of a clinical nutrition intervention, specifically a diet enriched with eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), on a severe CMS outbreak in a commercial sea farm. CMS was diagnosed in a single sea cage with high mortality rates. Histopathological analysis, RT-qPCR in situ hybridization for virus detection, and fatty acid composition analysis were used to monitor the impact of disease and the inclusion of EPA and DHA in heart tissue. Following the implementation of clinical nutrition, a decline in mortality rates, regression of CMS-associated changes, and a significant reduction in piscine myocarditis virus (PMCV) RNA load were observed within the salmon population. Fatty acid composition analysis of heart samples demonstrated increased levels of EPA and DHA, reinforcing the association between dietary factors, viral load dynamics, and overall fish health. Although further validation is needed in future studies, as field trials may not be sufficient to establish causation, our results indicate that optimizing the EPA + DHA levels may prove beneficial in severe CMS outbreaks.

Growth performance, gut microbiota composition, health and welfare of European sea bass (Dicentrarchus labrax) fed an environmentally and economically sustainable low marine protein diet in sea cages

The large use of fish meal/fish oil in carnivorous fish feeds is the main concern regarding environmental sustainability of aquaculture. Here, we evaluated the effects of an innovative diet, designed to be (1) environmentally sustainable by lowering the marine protein content while being (2) cost effective by using sustainable alternative raw materials with acceptable cost and produced on an industrial scale, on growth performance, gut microbiota composition, health and welfare of European sea bass (Dicentrarchus labrax), a key species of the Mediterranean marine aquaculture, reared in sea cages. Results show that the specific growth rate of fish fed the low marine protein diet was significantly lower than those fed conventional diet (0.67% vs 0.69%). Fatty acid profile of fillets from fish fed a low marine protein diet presented significant lower n-6 and higher n-3 content when compared to conventional ones. Then, a significant increase in the abundance of Vibrio and reduction of Photobacterium were found in the gut of fish fed with the low marine protein diet but effects on sea bass health needs further investigation. Finally, no major health and welfare alterations for fish fed the low marine protein diet were observed, combined with a potential slight benefit related to humoral immunity. Overall, these results suggest that despite the low marine protein diet moderately affects growth performance, it nevertheless may enhance environmental and economic sustainability of the sea bass aquaculture.

Safety and efficacy of a feed additive consisting of copper(II)-betaine complex for all animal species (Biochem Zusatzstoffe Handels- und Produktionsges. mbH).

Following a request from the European Commission, the Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) was asked to deliver a scientific opinion on the efficacy of copper(II)-betaine as a nutritional additive for all animal species and on the safety for the marine sediment when the additive is used in sea cages. The FEEDAP Panel concluded that the risk to the marine sediment is acceptable when the additive is used in sea cages. The additional statistical analysis of the results of the efficacy study already assessed in the previous opinion did not allow the Panel to conclude on the efficacy of the additive.

Assessment of the feed additive consisting of zinc chloride hydroxide monohydrate for all animal species for the renewal of its authorisation (NUTRECO Nederland B.V.).

Following a request from the European Commission, EFSA was asked to deliver a scientific opinion on the assessment of the application for the renewal of the authorisation of zinc chloride hydroxide monohydrate as a nutritional feed additive for all animal species (3b609). The applicant reported changes in the production process and requested a change in the specification of the additive. The EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) confirms that the use of the additive under the current authorised conditions of use is safe for the target species and the consumers. The use of the additive in animal nutrition at the proposed use levels for the terrestrial species and land-based aquaculture systems is considered safe for the environment. The FEEDAP Panel cannot conclude on the safety of the additive for marine sediment compartment, when it is used in sea cages. The additive is an eye irritant, but not irritant to the skin and not a skin sensitiser. The exposure through inhalation is likely, but in the absence of data, the Panel is not in a position to conclude on the risk of exposure by inhalation. There was no need for assessing the efficacy of the additive in the context of the renewal of the authorisation.

Nocardiosis and other common diseases of cultured golden pompano (Trachinotus blochii) in Taiwan.

Golden pompano (Trachinotus blochii) is a carnivorous teleost cultured in the Asia-Pacific region. Fish culture in high densities and numbers results in disease outbreaks, causing huge economic losses. Here, we collected cultured golden pompanos from 2021 to 2022 and identified the pathogens isolated from the diseased fish. Out of a total of 64 clinical cases observed in both sea cages and fish ponds, it was found that Nocardia seriolae was the predominant pathogen (26%), followed by Lactococcus garvieae (13%). Trichodina spp. was the most prevalent parasite in sea cages and earthen ponds (21%), while Neobenedenia spp. was the primary parasitic pathogen (16%) in sea cages. Given these findings, further investigations were conducted, including antibiotic susceptibility and pathogenicity tests specific to N. seriolae in golden pompanos. Antibiotic susceptibility tests of N. seriolae revealed that all strains were susceptible to doxycycline, oxytetracycline, florfenicol and erythromycin but resistant to amoxicillin and ampicillin. Additionally, a pathogenicity assessment was carried out by administering an intraperitoneal injection of 0.1 mL containing 107 CFU of N. seriolae per fish. The mortality rates observed varied between 40% and 90%, with the P2 strain exhibiting the highest level of virulence, resulting in a cumulative mortality of 90%. Therefore, disease outbreaks in fish can be minimized by developing effective treatments and prevention methods.

Timing of puberty in F1-generation hatchery-produced greater amberjack (Seriola dumerili)

We evaluated the onset of puberty of first-generation (F1) hatchery-produced greater amberjack (Seriola dumerili) reared in sea cages for 5 years. Fish were sampled every year in June, at the expected peak of the spawning period in the Mediterranean Sea. No sexual dimorphism in body weight was observed in the study. The ovaries of 1 and 2-year-old (yo) females consisted of primary oocytes only, while at the age of 3-yo early vitellogenic (Vg) oocytes were also identified, but with extensive follicular atresia. At the age of 4-yo, late Vg oocytes were observed, but again extensive follicular atresia characterized the ovaries of 50 % of females. At the age of 5-yo, follicular atresia of Vg oocytes was very limited. In males, gametogenesis was evident already in 1- and 2-yo fish, and 100 % of sampled 3-yo males produced collectable viable sperm. Plasma testosterone (T), 17β-estradiol (E2), and 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) remained similar in 3 – 5-yo females, with T and E2 levels being highest in females in advanced vitellogenesis or with significant follicular atresia, compared to immature females. In males, plasma T declined over the years, while 11-ketotestosterone (11-KT) and 17,20β-P were highest in 4 and 5-yo males, with spermatozoa motility characteristics being improved from the 4th year onwards. The administration of GnRHa implants to 5-yo fish induced only two spawns, albeit no fertilized eggs were obtained. The results indicate that hatchery-produced greater amberjack males mature well and within the same age observed in the wild, however with smaller gonad size. On the contrary, females mature later than in the wild, also with a smaller gonad size. Spawning in response to GnRHa treatment was not effective, suggesting that Mediterranean hatchery-produced broodstocks may be dysfunctional, and further research is needed to document any improvement as the fish get older, or to determine if the results may be related to the specific stock of fish.

Environmentally driven changes in Atlantic salmon oxidative status interact with physiological performance

Farmed Atlantic salmon in sea cages experience natural seasonal changes in seawater temperature and photoperiod. Atlantic salmon have more oxidized tissues in spring and early summer, and this corresponds to the period of increasing day length, temperature, and growth rate. However, the molecular mechanisms underlying the redox metabolism of Atlantic salmon exposed to the interaction of seasonal cues remain unclear. This study aims to investigate the effect of seasonal changes in temperature and photoperiod on the redox metabolism at the molecular level of Atlantic salmon. Salmon reared in tanks were subjected to simulated natural (for farmed salmon in sea cages) photoperiod and temperature to mimic spring and summer (March to August). We found that the changing photoperiod and temperature, which were simulated to spring and summer conditions, influenced the redox metabolism of Atlantic salmon over the experimental period. We showed that increased utilization of tissue antioxidants such as vitamin C, vitamin E, and reduced glutathione in the spring was restored in August. The more reduced glutathione-based redox potentials and the low levels of malondialdehyde (MDA) in August in liver and muscle suggest lowered tissue oxidative activity at that time. We further revealed that the expression profiles of genes involved in growth hormone signaling and cell cycle regulation were correlated with oxidative stress patterns. Together, these promising results reveal the molecular mechanisms underlying the ecological implications of oxidative status. The study provides new insight into the possible role redox signaling plays in the growth regulation of fish to the seasonal shift in environmental factors.

Molecular Investigation of Aquatic Reoviruses in Rainbow Trout in Northern Türkiye: The First Molecular Detection of Aquareovirus A in Türkiye

Aquareovirus A (AqRV A) has been known to cause low or intermediate diseases among various salmon species and mollusks. Additionally, Piscine orthoreovirus (PRV), divided into subtypes PRV-1, PRV-2 and PRV-3, has been reported in rainbow trout, coho salmon and Atlantic salmon. In this study, we investigated the presence of these aquatic reoviruses in rainbow trout in Turkiye. For this purpose, fish were collected from 5 cities (Sinop, Samsun, Ordu, Trabzon and Rize) in Turkiye`s Black Sea Region. In total, 150 fresh rainbow trout (30 fish per city) of 25–35 cm were collected from fishmongers. All the genotypes of Piscine orthoreoviruses (PRV) and Aquareovirus A were investigated using RT-PCR with degenerated pan-specific primers. No PRV genotypes were detected, but 4 pools of 30 pools were positive for AqRV A. According to phylogenetic analyses of segment 10 (VP7), all viruses were closely related to the Chum salmon reovirus (CSRV) belonging to AqRV A (GeneBank Accession number: NC_007590.1). This is the first report of AqRV A in naturally infected rainbow trout cultivated in sea cages in the world, necessitating further investigation of the pathobiology of AqRV A in rainbow trout.

Aquaculture in Algeria: Current Status, Analysis, and Considerations for Commercial Development

Aquaculture in Algeria has developed significantly since the 1920s, primarily focusing on oyster and mussel farming. Establishing the Ministry of Fisheries and Marine Resources (MPRH) in 1999 marked a crucial milestone for the industry. Despite challenges in data collection, Algerian aquaculture production reached only 4,779.29 tonnes in 2021, showing a mere 0.2% of African production and 0.0044% of world aquaculture production. More than half of production comes from marine fish cultured in private-sector sea cages. However, shrimp production is almost null. The taxonomic composition of Algerian aquaculture is diverse, with marine and freshwater fish species playing prominent roles. Despite these challenges, the aquaculture field in Algeria has demonstrated an impressive annual growth rate of 12.49% and receives continuous government support. Nevertheless, limited infrastructure, a shortage of expertise, and the need for further research pose significant obstacles. Efforts are underway to integrate aquaculture with agriculture in Saharan zones, further facilitated by governmental support. Overcoming challenges and promoting sustainability through strengthening research capacities, fostering collaboration, and providing financial support is crucial for the advancement of industry. By addressing challenges and embracing sustainability, the aquaculture sector in Algeria can unlock its full potential, ensuring food security, economic growth, and environmental sustainability.

Tryptophan and Cortisol Modulate the Kynurenine and Serotonin Transcriptional Pathway in the Kidney of Oncorhynchus kisutch.

Aquaculture fish are kept for long periods in sea cages or tanks. Consequently, accumulated stress causes the fish to present serious problems with critical economic losses. Fish food has been supplemented to reduce this stress, using many components as amino acids such as tryptophan. This study aims to determine the transcriptional effect of tryptophan and cortisol on primary cell cultures of salmon head and posterior kidney. Our results indicate activation of the kynurenine pathway and serotonin activity when stimulated with tryptophan and cortisol. An amount of 95% of tryptophan is degraded by the kynurenine pathway, indicating the relevance of knowing how this pathway is activated and if stress levels associated with fish culture trigger its activation. Additionally, it is essential to know the consequence of increasing kynurenic acid "KYNA" levels in the short and long term, and even during the fish ontogeny.

Atlantic salmon (Salmo salar) distribution and vertical size-stratification in a commercial sea cage: A case study

Biomass and size estimates of fish are most valuable information to assure optimal management in Norwegian Atlantic salmon production. Such estimates are largely based on models and small samples of few individuals, and improvements are required for better representativity. Advances in machine learning triggered fast development of automated size estimation using stereovision cameras. These measurement systems can result in precise measurements of individual fish. Nevertheless, fish behavior needs to be considered for a proper description of the true mean and variation of fish sizes of cage populations because salmon distribution is not homogeneous in sea cages. Most studies on salmon distribution were performed in relatively small sea cages and additional experiments at commercial scale are required to verify that previous findings are applicable under industrial conditions. In this case study, we monitored vertical and horizontal distributions of salmon in a commercial sea cage. Vertical size stratification was investigated using stereovision cameras, and salmon and growth-stunted fish abundances and swimming speed were measured using cameras recording simultaneously in 16 positions: four horizontal positions and four depths (1 m, 5–6 m, 9–11 m and 14–16 m), four times during one day. Our results suggest a heterogeneous vertical distribution with longer individuals found deeper in the sea cage at high abundance and swimming more slowly than smaller individuals, including growth-stunted fish, found in low abundance close to the surface. Cumulative mean fork-lengths per depth were compared to the estimated true mean fork-length for the whole population of the cage and results show that automatic biomass and size estimation based on a single depth likely results in biased size estimation for the cage population. On the contrary, horizontal distribution appeared homogeneous, and our data supports the assumption that fish were exhibiting a circular swimming pattern, as previously described in small sea cages and under slow current conditions. Our study adds data to currently still scarce knowledge about fish behavior and distribution at commercial scale and provides indications on the use of new technologies for biomass and size estimation. Further studies on longer timelines and different locations are necessary to further generalize behavioral models.

An integrated techno-economic decision-support fiscal forecast model for sea cage mariculture enterprises for Asian seabass production in Indian territorial waters

Cage-based mariculture ventures in India are expanding, particularly emerging with the most sought-after candidate Asian seabass Lates calcarifer in territorial waters. However, comprehensive techno-economics have not been attempted, and thus hindering the sector's growth potential. To address this, a spatiotemporally validated decision-support model was developed to optimize investment decisions and forecast economic performance. Peer-reviewed contextual data was used to establish scientifically valid assumptions, and robust scenario simulations were conducted to benchmark production systems and species performance. Unit standards were defined and benchmarked for metric deployment for the first time. Capacity Utilization (CU) was found to be critical for success, achieving break-even at 31% CU with set model specifications derived from an inverse linkage with market price dynamics. The enterprise model demonstrated significant economic potential over a ten-year horizon, with low risk due to current policy initiatives by the Indian government. Furthermore, the model architecture and benchmarked specifications derived are adaptable to other candidates with its species-specific biological parameter application. The study can aid stakeholders in planning the enterprise budget. Most importantly, the study highlights the advantages of integrating technological, biological, and financial approaches to mitigate risks and promote the mariculture sector in India. The adaptability of the Asian seabass to farming systems, technical feasibility, and the availability of seeds and suitable sites along the Indian coast have been influential factors and these attributes in specific underpins the profitability. This research provides a way forward for the future of the sector in India, particularly with regard to farming of the Asian seabass, and emphasizes the importance of techno-economic models (TEM) in promoting strategic development of the mariculture sector through open sea cage farming.

Model of Oxygen Conditions within Aquaculture Sea Cages.

To ensure optimal feed intake, growth, and general fish health in aquaculture sea cages, interactions between drivers that affect oxygen conditions need to be understood. The main drivers are oxygen consumption and water exchange, caused by flow through the cage. Swimming energetics in rainbow trout (Oncorhynchus mykiss) in normoxia and hypoxia at 10, 15, and 20 °C were determined. Using the determinations, a conceptual model of oxygen conditions within sea cages was created. By applying the model to a case study, results show that with a temperature increase of 10 °C, oxygen concentration will decrease three times faster. To maintain optimal oxygen concentration within the cage, the flow velocity must be increased by a factor of 3.7. The model is highly relevant for current farms since the model predictions can explain why and when suboptimal conditions occur within the cages. Using the same method, the model can be used to estimate the suitability of potential new aquaculture sites.

Trawl-related mortality and injuries to the southern king crab Lithodes santolla of Patagonia

The catch and discard of non-target species could have detrimental effects on bycatch, species due, among others, to the increase in mortality and prevalence of injuries. In Argentina, the southern king crab (SKC), Lithodes santolla, supports a profitable trap fishery but is also caught as bycatch in trawl fisheries. The aims of this work were: i) to quantify the mortality and injuries in SKC caught as bycatch in the hake fishery in San Jorge Gulf (southwestern Atlantic Ocean), ii) to assess the factors that affect their mortality and injury occurrence, and iii) to estimate their postdiscard mortality.Immediate mortality (IM) and injuries in SKC were recorded in hauls of the hake fishery, and then related to operational and biological variables. SKC vitality was assessed using the reflex action mortality predictor (RAMP) test. Postdiscard mortality was analyzed in aquaria and wild (sea cages) conditions. The IM of SKC in the common hake fishery was 31%. The IM, as well as increased injuries and decreased vitality, were directly associated with the time and conditions of air exposure. Both the IM and injury occurrence were also affected by biological variables such as the sex,size and molt stage. Postdiscard mortality was lower in wild conditions than in the aquaria (1%). Our results suggest that SKC could have high resistance to handling and high recovery capacity after its return to the sea. In consequence, the quick return of SKC to the sea may have a positive effect on SKC survival.

Future climate change accelerates the invasive rhythm of alien marine species: New insights into the invasive potential of the world's aquaculture species red drum Sciaenops ocellatus

In recent decades, an unprecedented frequency of red drum (Sciaenops ocellatus) escapes from sea cages (i.e., million tail level) has generated enormous pressure on local marine biodiversity and ecosystems. This study aimed to assess the distribution and shifts of hotspot fitness zones for S. ocellatus under global climate change and to identify the trophic levels in the coastal waters of China. The species distribution model (SDM) identified four hotspot fitness zones at a global scale located in the Atlantic Ocean along the Gulf of Mexico and Uruguayan coasts, and in the Pacific Ocean along the Chinese and Australian coasts. Under global warming and climate change, the most suitable habitat for S. ocellatus would expand (448,178.6 km2) and the centre of mass would shift northwards. Stable isotope δ15N and δ13C ratios indicated S. ocellatus has very high ecological competition, within a wide feeding range and high ecological position (δ15N: 10.84 ∼ 12.84 ‰, 11.61 ± 0.62 ‰; δ13C: −15.28 ∼ -17.25 ‰, −16.45 ± 0. 52 ‰) in the escape zone. The results suggested that a wide range of habitats, high reproductive capacity, and ecological niche competition conferred escaped S. ocellatus with a great ability to invade across regions on a global scale.

Nighttime Lighting Influences on the Plankton Feeding and Growth of Juvenile Pacific Bluefin Tuna, Thunnus orientalis.

During fingerling production of Pacific bluefin tuna (PBF) Thunnus orientalis, heavy mortality can occur immediately after juveniles are transferred from nursery tanks to sea cages; however, nighttime lighting can moderate this mortality. Additionally, various live prey aggregate due to nighttime lighting in practical sea cage culture of PBF. Here, we investigated whether the growth and viability of PBF juveniles could be improved through promoting feeding on live prey that aggregate under nighttime lighting. Two treatment groups were established using land-based tanks under constant environmental conditions, one in which the juveniles were fed live prey at night (night-feed in four replicate tanks) and the other in which juveniles were not fed during the night (control in four replicate tanks). Although the survival rate did not differ significantly between the two groups, growth was significantly improved in the night-feed group, in which 69-78% of the juveniles showed evidence of feeding during the night. Thus, nighttime lighting plays a vital role in the aggregation of various live prey. PBF juveniles consume these prey in sea cages, which promotes their growth. This may partially serve as a countermeasure against the heavy mortality observed in sea cages.

Black soldier fly larvae (Hermetia illucens) meal is a viable protein source for Atlantic salmon (Salmo salar) during a large-scale controlled field trial under commercial-like conditions

Black soldier fly larvae meal (BSFL) from Hermetia illucens is a promising alternative protein source in diets for farmed fish. The larvae can efficiently convert low-value organic material into high-value protein in a production cycle with low arable land and freshwater inputs. A few recent studies have shown that BSFL is a suitable protein source for Atlantic salmon (Salmo salar) in smaller controlled experiments. However, industry-relevant field trials conducted under large scale near-commercial conditions over a longer period are lacking. In this study, a feeding trial was performed to evaluate the impact of BSFL on growth performance and health of Atlantic salmon during the grow-out phase in seawater, in a commercial site in Vestland county, Norway. A total of 181,046 post-smolt Atlantic salmon were distributed into six duplicate sea cages and fed one of three diets (commercial-like control diet and two test diets partially replacing the protein content of the control diet with 4% and 8% defatted BSFL meal) for 21 weeks, until a relevant commercial slaughter size of 4.5–5.0 kg was reached. Health parameters were assessed, including histology of the distal intestine (DI), DI microbiota identification (by 16 s rRNA-seq) and salmon RNA-seq of DI and head kidney (HK). The results showed that the inclusion of BSFL meal supported growth performance and had no adverse effect on gut health. The beta diversity of the DI microbiota and the relative abundance of families Lactobacillaceae and the chitinolytic Bacillaceae increased in the fish fed the BSFL diets. Additionally, no histopathological changes were attributable to BSFL meal intake. Results from RNA-seq in DI revealed that BSFL inclusion modulates metabolic processes associated with lipids, response to estrogens, activity of immune receptors (to chemokines), phagocytosis and extracellular vesicles. Based on these results, black soldier fly larvae meal was shown to be a suitable alternative protein ingredient in inclusions of up to at least 8% for Atlantic salmon under industrial fish farming conditions.

The reproductive potential of Pacific bluefin tuna (Thunnus orientalis) farmed in sea cages in South Korea

AbstractIdentifying environmental effects on the reproduction cycle and sex hormones is essential for ensuring the sustainable productivity of Pacific bluefin tuna (PBT, Thunnus orientalis) aquaculture. In the present study, 70 PBTs, commercially farmed in sea cages near Yokjido Island, South Korea, were investigated from April 2020 to March 2021. Environmental data, including water temperature and photoperiod duration, were collected. The gonadosomatic index (GSI) was calculated, and male and female maturity stages were classified monthly in proportions based on histological analysis of the gonads. Male and female gonadal developmental stages were classified into four major stages. Mature male and female PBTs were observed from May to August and June to August, respectively. Monthly changes in sex steroid hormone levels in PBT plasma were evaluated. The GSI and sex steroid hormones of males and females increased in May, peaked in June, and decreased thereafter. Our results confirmed the reproductive potential of farmed PBT and verified that reproductive maturity is reached in July. This study, to the best of our knowledge, is the first to investigate the reproductive biology of PBT in South Korea, and our results constitute a reference for future research on PBT aquaculture.

Terrestrial Compound Protein Replacing Dietary Fishmeal Improved Digestive Enzyme Activity, Immune Response, Intestinal Microflora Composition, and Protein Metabolism of Golden Pompano (Trachinotus ovatus).

Terrestrial compound protein (Cpro) can be potentially used to replace fishmeal (FM) in the marine carnivorous teleost, golden pompano (Trachinotus ovatus). Four isonitrogenous (45%) and isolipidic (12%) diets named FM30, AP80, PP80, and CP80 were formulated. FM30 (control) contained 30% FM and 25% basic protein, while AP80, PP80, and CP80 only contained 6% FM, where 80% FM and 25% basic protein of control diet were completely replaced by animal protein, plant protein, and Cpro, respectively. After golden pompano juveniles (initial weight: 10.32 ± 0.09 g) were, respectively, fed the four diets in floating sea cages for 10 weeks, the growth performance, intestinal digestive enzyme activity, and immune responses, protein metabolism indices of the CP80 group were similar to or better than those of the FM30 group (P > 0.05), and significantly better than those of the AP80 and PP80 groups. Specifically, the weight gain (WG), feed conversion ratio (FCR), activity of alanine transaminase (ALT), growth hormone (GH), and insulin-like growth factor-1 (IGF-1) contents of serum, mRNA level of interleukin-10 (il-10), zonula occludens-2 (zo-2), claudin-3, claudin-12, and eukaryotic translation initiation factor 4G (eif4g) were significantly higher, and the activity of α-amylase (AMS), lipase (LPS) in the foregut and midgut, interleukin-8 (il-8) expression in the intestine was significantly lower than that in the CP80 group, compared with those in AP80 and PP80 groups (P < 0.05). Moreover, the intestinal microflora composition of golden pompano fed with the CP80 diet was improved. Specifically, at the phylum level, the relative abundance of harmful bacterial strains cyanobacteria and TM7 of CP80 group was similar to those of FM30 group (P > 0.05), but was significantly lower than those of AP80 and PP80 groups (P < 0.05). At the genus level, the beneficial bacterial strains Agrobacterium and Blantia of CP80 group were also similar to those of FM30 group (P < 0.05), which were significantly higher than those of AP80 and PP80 groups, but the beneficial bacterial strains Bifidobacterium and Devosia of CP80 group were significantly higher than that in the other groups (P < 0.05). Besides, in diet CP80, the contents of amino acids and anti-nutritional factor, as well as the in vitro digestion rate were comparable to those of FM30, and the anti-nutritional factor content was between AP80 and PP80; total essential amino acids (EAAs) and methionine contents were higher than those in AP80, the glycine content was higher than that in PP80. Taken together, these results indicated that the CP80 diet had better amino acid composition and relatively low content of anti-nutritional factors, as well as high-digestion rate, and thus leads to the fish fed CP80 displaying improved effects in digestive enzyme activity, immune response, protein metabolism, and intestinal microbiota composition, which may be the important reasons to explain why that 80% of FM can be replaced by Cpro in the diet of golden pompano.