Aquaculture Research最新文献

Apostichopus japonicus is one of the few animals that can synthesize saponins. Present understanding of saponin biosynthesis is often limited to genome analysis, leaving the precise mechanism still unclear. This study examined the potential role of a gene annotated as farnesyl pyrophosphate synthase (FPS) in saponin biosynthesis of A. japonicus. We amplified its complete cDNA (denoted as AjFPS) and produced its recombinant protein (rAjFPS) through rapid amplification of cDNA ends (RACE) and Escherichia coli expression system, respectively. RNA interference and correlation analysis of AjFPS transcriptional expression level and saponin content were conducted to evaluate the role of AjFPS in saponin biosynthesis. A pull-down assay was used to preliminarily explore its regulatory role in saponin biosynthesis. The complete cDNA sequence of AjFPS was shown to be 3,006 bp in length. The inferred amino acid sequence harbored two conserved aspartate-rich sites (DDXXD). Analysis of the amino acid sequence using phylogenetics showed that AjFPS was more similar to FPSs found in saponin-producing marine organisms rather than those in non-saponin-producing ones or plants. The knockdown of AjFPS resulted in a remarkable decline in saponin content. The temporal expression of AjFPS was significantly correlated with the variation in saponin content after Vibrio splendidus challenge. The pull-down analysis illustrated that AjFPS interacted directly or indirectly with diverse immune-related factors associated with pathogen recognition and destruction and protection against oxidative stress. Combined, these results suggested that AjFPS is involved in saponin synthesis, and this process in A. japonicus is likely modulated by immune processes, with AjFPS serving as a regulatory node. These findings will promote a deeper understanding of saponin synthesis and immune regulation as well as contribute to the improvement of saponin quality traits in cultured A. japonicus.

When bivalve aquaculture production relies on natural recruitment, yields may decline due to density-independent constraints at multiple life stages. These life stage transitions include larval settlement, which is typically variable with rapid losses of newly settled individuals and the additional mortality from predation or abiotic factors (e.g., temperature, desiccation, and physical disturbance) as the bivalves grow. Recruitment monitoring and outplants were used to evaluate the potential limiting factors affecting different life stages in two nonnative clam species, Manila clams, Ruditapes philippinarum, and softshell clams, Mya arenaria in Willapa Bay, Washington, USA. Recruits (250–500 µm) did not differ in cumulative abundance in 2023 relative to prior years of monitoring (five recruitment seasons between 2011 and 2017). Recruits surviving to the end of the summer represented 12% or less of those that had arrived, but still showed spatial patterns consistent with rates of arrival. Manila clams outplanted across an elevation gradient suffered high mortality below mean lower low water regardless of size class (small: 8 mm and large: 20 mm), where native rock crabs (Cancer productus) were abundant. Clam growth declined at higher tidal elevations consistent with inundation time. European green crabs (Carcinus maenas) were relatively abundant at midtidal levels where commercial clam aquaculture typically occurs in the bay and where small clams were particularly reduced without predator protection from mesh. While these data support that green crabs may be reducing survival of 1-year-old clams at midintertidal elevations, they also identify earlier bottlenecks to repopulating commercial clam beds, which point out why seeding clams is used to maintain consistent production. Further exploration is needed before green crabs can be singled out as a new limit on clam yields relative to the roles of predation across the size classes of clams in Willapa Bay.

Hatchery release of rock bream (Oplegnathus fasciatus) is common in the Zhoushan Sea region of the East China Sea as an efficient method for stock enhancement. Clarifying the genetic effects of farm-raised populations on wild ones is important for understanding the health of fish stocks. Thus, this study collected six rock bream stocks (two wild, three hatchery-reared, and one parental) for genetic diversity analysis using microsatellite markers and mitochondrial sequences. Although the results of mitochondrial sequence analysis showed that 61.26% of the genetic diversity resided among groups, indicating a high degree of genetic differentiation among wild, hatchery-reared, and parental groups, the results of microsatellite analysis showed that 30% of the genetic diversity resided within the populations, indicating no obvious genetic differentiation among different groups. Our study suggests that though releasing hatchery-reared rock bream for stock enhancement may not noticeably decrease the genetic diversity of wild populations in the Zhoushan Sea in the short term, long-term genetic evaluations shall be taken to monitor genetic diversity in wild rock bream and ensure that the populations remain healthy.

Vaccination is an approved novel approach for controlling aeromonads disease caused by Aeromonas hydrophila. This study aimed to optimize the A. hydrophila vaccine candidate with a protective efficacy of 71.4% through immersion. A total of 600 tilapia fingerlings weighing 10–15 g were collected and distributed in tanks at Magadu farm. The fingerlings acclimatized for 2 weeks. Vaccination was done by immersion at a dose of 1.6 × 10⁸ cfu/mL mixed as 1 part of a vaccine in 20 parts of tank water. A total of 150 fingerlings were exposed to a vaccine for 30 min and distributed in three replica tanks, each having 50 fingerlings. The same procedure was applied to fingerlings exposed to the vaccine at 45 and 75 min, while the remaining 150 fingerlings served as control. Fish were bled at day 0 and days 7, 14, 21, and 28 postvaccinations for immunogenicity studies. A challenge trial with a virulent A. hydrophila followed. Observation for mortalities and clinical signs was made for 28 days postchallenge. No clinical signs and death were observed during the entire period of 28 days postvaccination. The serology findings showed higher antibody titer of 45 min vaccination time of exposure (GMT log 2 = 5.0 at day 28). The findings revealed that the protective efficacy had increased to 90% relative percent of survival at 45 min duration of vaccine exposure. The vaccine demonstrated acceptable safety and protection levels on the field.

Takifugu genus pufferfish are popular in East Asian countries such as Korea, Japan, and China, but they are avoided as aquaculture species due to slow growth, high cannibalism rates, and susceptibility to diseases. Hybridization is considered one of the most important and efficient breeding methods for aquatic animals, and recent studies have been conducted on hybridization. This study compared optimal water temperature and salinity ranges for hybrid pufferfish by examining three water temperature conditions (15, 20, and 25°C) and five salinity conditions (0, 3, 10, 25, and 33 psu). The hatching rates of hybrid pufferfish embryos were 65.3%, 63.5%, and 67.7% at 0, 3, and 10 psu, respectively, while all embryos died at 25 and 33 psu. Hybrid pufferfish larvae had the highest survival rates at 20°C, and growth rates increased with rising water temperatures. In the salinity experiment, survival rates were 86.0%, 85.0%, 88.0%, and 88.5% at 3 psu, 10 psu, 25 psu, and 33 psu conditions, respectively, with the highest growth observed at 25 psu conditions. Hybrid pufferfish embryos showed good survival in freshwater, but all died in seawater. However, larvae showed good survival and growth in seawater, while all died in freshwater. Therefore, rearing hybrid pufferfish embryos seem suitable at salinities of 10 psu or lower, and increased resistance to salinity was observed in hybrid pufferfish after hatching, indicating that rearing under various salinity conditions ranging from 3 to 33 psu may be feasible.

Blooms of Microcystis are common in fish ponds in Bangladesh which vary distinctly with season to season. A study on the seasonal changes of Microcystis and Anabaena was carried out over a period of 12 months from March 2021 to February 2022 in two rural fish ponds to see the effect of environmental factors on the seasonal dynamics of these two species. Cyanobacterial community comprised of seven genera and 15 species of which Microcystis was found to be the most dominant genus. Overabundance of Microcyctis may suppress the growth of Anabaena and other microalgal species. In both ponds, Microcyctis was found to be the dominant during the summer and the spring, whereas Anabaena was only characterized in summer. Moderately higher temperature, nitrate–nitrogen, and phosphate–phosphorus enrichment increased the biomass of both Microcystis and Anabaena. Microcystin was found in all the seasons with the highest quantity in summer in the cyanobacteria samples collected from both of the ponds. The highest concentrations of MCs were 22 and 65 μg/L of the sampled water during the peak bloom period of blue-green algae in pond 1 and pond 2, respectively. The high concentration of microcystin in water seems to be a pernicious warning for aquatic organisms as well as human health. Further studies in detail on the relationship between microcystin and cyanobacterial growth under different environmental factors seem to be necessary.

In recent years, more attention has been paid to the application of host-associated microorganisms as an appropriate source of probiotics in aquaculture. These probiotics promoted effective colonization and application and provided better benefits than other sources. A total of 32 isolates were collected from the water, shrimp, and sediment of the cultured pond of Litopenaeus vannamei. Probiotic effects were comprehensively evaluated by extracellular enzyme activity, virulence genes detection, bacteriostatic activity, drug susceptibility test, tolerance to adverse environment, and challenge experiment. Six of these isolates exhibited bacteriostatic activity against pathogens, such as Vibrio cholerae, V. owensii, V. fluvialis, V. campbellii, V. rotiferianus, Photobacterium damselae, V. vulnificus, and V. parahaemolyticus. Using 16S rRNA gene sequencing analysis, isolates were identified as Bacillus subtilis (P8, P29, and P30), B. velezensis (P12), Prestia flexa (P21), and Cytobacillus firmus (P23). They were tolerant to high temperature, low acid (pH 2.0), bile salt (2%), and the simulated gastrointestinal environment, secreting phospholipase, amylase, protease, gelatinase, and lipase. They were sensitive to only two or fewer drugs among 27 antibacterial drugs and did not carry any of the tested virulence genes. Biosafety in vivo evaluations showed that they were safe for Ctenopharyngodon idella (P12 ＞ P23 ＝ P29 ＞ P8 ＞ P30 ＝ P21). The results suggest that P8, P12, P23, P21, P29, and P30 have high probiotic potential and can be used as good probiotics in aquaculture and the development of ecological preparations.

The interplay between environmental, biological, and physical factors often leads to the deterioration of dead fish in marine cages prior to their removal. Depending on the weight of the dead fish and the frequency of their removal, deterioration can progress to a stage where visual identification by divers becomes challenging, thereby disrupting accurate counting of dead fish. This study presents a practical precision tool for monitoring the number of dead fish during the pregrowth and growth phases of caged European sea bass (Dicentrarchus labrax). To improve the assessment of collected mortality, experiments were conducted in farming cages with various fish weights. Identifiable fish rates (I, %) were calculated every 24 hr and classified into four weight classes: WC1 (4–15 g), WC2 (15–30 g), WC3 (30–80 g), and WC4 (>80 g). The corrected number of dead fish (M) was calculated by dividing the collected number (C) by a correction factor (McR), which was determined based on the adopted removal frequency. The possible mortality removal frequencies per week (Fn) included operations such as F7 (daily), F3 (3 times), F2 (2 times), and F1 (once). The smallest correction denominator was 22% for WC1 at a frequency of once per week, whereas the maximum was 100% for WC3 and WC4 daily. The results revealed a high negative significant correlation between Fn and uncollected degraded fish rate (UR) (r = –0.841, p < 0.05). Applying corrections to mortality collected in three finished batches (B2, B3, and B7) led to an increase in the mortality rate by 3.9% ± 1.5%, 5.5% ± 0.7%, and 5.0% ± 0.5%, respectively. This explained 16.8% ± 4.7%, 65.5% ± 26.7%, and 30.3% ± 3.7% of fish disappearances in B2, B3, and B7, respectively. The significance of this study lies in its practical applicability to fish farms as a precise tool for monitoring fish raised in marine cages.

Although enrofloxacin (ENR) is an important pharmaceutical in aquaculture for its excellent efficacy, it is mostly utilized through an off-label prescription system. Thus, the optimal clinical use regimen is not well-established. A series of studies was performed to obtain pharmacological and safety data needed for the use of ENR, a synthetic fluoroquinolone, in treating bacterial diseases occurring in black rockfish, Sebastes schlegelii. Minimal inhibitory concentrations showed that ENR exerts a potent in vitro efficacy inhibiting the growth of several pathogenic bacteria at concentrations less than 1 mg/L. ENR with oral doses of 5 mg/kg and up for 1 week significantly prevented mortality of black rockfish infected with Streptococcus iniae and Aeromonas salmonicida, demonstrating in vivo efficacy. Complete protection was obtained against these two bacteria by 10 mg/kg ENR in this in vivo infection trial. Black rockfish did not exhibit any severe abnormal signs by ENR up to 20 mg/kg when assessed by basic haematoclinical and histopathological parameters. Efficacy and toxicity study results collectively suggest that oral dose of 10 mg/kg ENR is optimal to treat bacterial infections. Through muscle residue analyses, the required withdrawal period for safe fish consumption was found to be approximately 90 days by measuring clearance of ENR and its metabolite ciprofloxacin (CIP). This study provides necessary information for the use of ENR to treat two frequently-occurring bacterial infections, Streptococcus iniae and Aeromonas salmonicida in black rockfish. Obtained data can be the basis for an official guideline for aquacultural ENR use.

In an era of striking climate change, increased marine temperature severely affects aquatic animals and cause significant ecological and socioeconomic impacts. At present, there is little information about the effects of heat stress on the physiology of greater amberjack (Seriola dumerili). This study explores the mechanisms whereby juvenile greater amberjacks cope with heat stress. An increase in water temperature (25 to 28°C and 31°C) changed the activity levels of enzymes responsible for antioxidant defense, immune function, and energy metabolism. When water temperatures increased from 25 to 28°C and 31°C, the levels of malondialdehyde (MDA) and glucose (GLU) in the greater amberjacks increased, suggesting that the fish suffered oxidative stress. During the early stage of heat stress, the levels of triglycerides (TG) and glutathione (GSH) and the activities of superoxide dismutase (SOD), catalase (CAT), alkaline phosphatase (ALP), acid phosphatase (ACP), lysozyme (LYZ), alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), and succinate dehydrogenase (SDH) increased significantly suggesting that juvenile greater amberjacks adapt to heat stress by enhancing their antioxidant defense, energy metabolism, and immune defense. However, long-term exposure to heat stress decreased the levels of TG and GSH; decreased the activities of SOD, CAT, ALP, ACP, LYZ, and AST; and increased the levels of MDA and GLU, suggesting that the energy metabolism and immune function of juvenile greater amberjack S. dumerilis are suppressed by oxidative damage. This study provides insights into the physiological adaptation of juvenile greater amberjacks to heat stress.