Aquaculture, Fish and Fisheries最新文献

Aquaculture is becoming increasingly important for the world's food production. Recirculating aquaculture system (RAS) has a reduced water requirement and better possibilities for waste handling. Unfortunately, off-flavours can be formed in RAS and concentrate on fish flesh. Off-flavour compounds cause earthy, musty or other unwanted flavours to fish flesh that consumers find objectionable. Typically, off-flavours are removed by depurating the fish in clean water, but it often takes from days to weeks to fully remove these unwanted flavours that causes additional costs to fish producers. Therefore, reliable methods to reduce the need for depuration are needed. In this study, two methods were investigated for the removal of off-flavours in RAS rearing rainbow trout Oncorhynchus mykiss: an advanced oxidation process (AOP) using a combination of ozone (O₃) and hydrogen peroxide (H₂O₂), and a treatment with H₂O₂ alone. Two treatments (AOP and H₂O₂) and a control without oxidants were applied across nine identical experimental RASs for 8 h day⁻¹ over 10 days, and selected off-flavour compounds in water and fish were analysed. In fish, the concentrations of GSM and MIB were on average 776 and 962 ng kg⁻¹ (AOP) and 688 and 919 ng kg⁻¹ (H₂O₂) compared to 1071 and 1205 ng kg⁻¹ in the controls. The results showed that intensive oxidant treatments reduced the off-flavour concentrations in the recirculating water and in fish, which can potentially lead to reduced depuration time and production costs. Further optimization of the treatment is needed to improve off-flavour removal efficiencies.

Great Bay Estuary (GBE) is a complex estuarine system at the convergence of seven rivers, ocean and land. The GBE ecosystem supports typical estuarine species but, like many estuaries, has been a target of both invasive and range-expanding species. The goal of this study was to compare abundance, sex and size distribution of green crabs between oyster farm sites and non-farmed sites within GBE in 2021 and 2022. Overall catch was higher in 2021 compared to 2022. The highest population of green crabs was estimated to be in the farm area around Cedar Point, and natural/restoration area near Moody Point had the smallest European green crab population. In both years, the majority of green crabs captured (98%) were adult males, and few were juveniles captured. At the last sampling date of 2021 and 2022, most crabs were large (68 ± 0.5 mm and 63 ± 2 mm carapace width, respectively). Shellfish growers, restoration and management teams could use these data in mitigation strategies to sustain industries and enhance GBE health. This information is important for oyster restoration initiatives and oyster growers as they may want to: consider putting traps around their restoration reefs and farms to help reduce green crab infestation/predation in their growing areas; make decisions regarding best management practices and optimal growing locations when applying for permits; and work with management teams with gear improvement, such as floating gear, to reduce green crab intrusion into cages. High-priority locations for trapping should be areas such as oyster farms, oyster reefs and restoration sites.

Many countries and regions around the world have been adversely affected by the invasive spread of the largemouth bass (Micropterus nigricans). The breeding practices developed in China can serve as a reference for these regions to manage this species scientifically while providing high-quality protein for human consumption. As its introduction from Taiwan in 1983, the largemouth bass has become one of the most significant high-quality freshwater farmed fish in mainland China. The country has developed new varieties that exhibit faster growth rates and enhanced adaptability to artificial compound feed, leading to widespread aquaculture across the nation. This article systematically reviews the technological advancements in the introduction, breeding, reproduction and rearing of fry and fingerlings of largemouth bass in China over the last 40 years. After summarizing the progress in general breeding as well as fry and fingerling rearing technologies, we analyse three successful early breeding and out-of-season breeding modes developed in China. The advancement of innovative and practical breeding and seedling technologies has addressed the challenges of natural breeding in regions with relatively low temperatures, where it is not feasible to raise local fry to a marketable size for consumption within the same year. This progress significantly enhances largemouth bass aquaculture in China.

This study is the first to investigate the reproductive traits of Lobocheilos ovalis (n = 621), Rasbora argyrotaenia (n = 507) and Tor tambra (n = 138) through detailed gonad histology. We collected L. ovalis and R. argyrotaenia specimens from September 2017 to August 2019 and T. tambra from July 2018 to August 2019 from tropical rainforest streams in Ulu Temburong National Park Brunei Darussalam. In all three species, females were larger and attained sexual maturation at larger sizes than males. Gonad histology categorized five reproductive phases in the ovarian and testicular maturation cycle comprising the immature, developing, spawning capable, regressing and regenerating phases. Ovarian histological markers of the reproductive phases included increasing oocyte diameters and gradual changes in cytoplasmic and nuclear features. In testes, decreasing nuclear diameters, darkening nuclear stains and germinal epithelium continuity were significant histological markers. Monthly frequencies of reproductive phases showed that L. ovalis and R. argyrotaenia were reproductively active throughout the year, whereas T. tambra exhibited protracted spawning over several months. Gonad histology also revealed asynchronous ovarian development and batch spawning, facilitating these species’ year-round and protracted spawning. This reproductive strategy may be an adaptation for these species to increase the survival of offspring in hillstream habitats where flash floods are common. The present study significantly fills existing knowledge gaps in Southeast Asian cypriniform fishes, providing a reference point for gonad histology to elucidate the reproductive traits and ecology, particularly for the Lobocheilos, Rasbora and Tor genera. Importantly, it provides practical insights for the conservation and management of the wild populations of these species.

In recent lab-based experiments, some post-smolt Atlantic salmon (Salmo salar) held at 3°C for 5 weeks exhibited a range of clinical signs. They became lethargic and swam at the water's surface, developed ulcers to the head and jaw (clinical signs similar to tenacibaculosis in Norwegian salmon aquaculture) and had fin erosion, and this was associated with significant mortalities. In addition, when fish with ‘early’ and ‘advanced’ stages of these different clinical signs were further examined, their livers were found to be large, pale and friable. Fish with this aetiology also had elevated aspartate aminotransferase levels (indicative of liver damage), elevated plasma [Na⁺], [Cl⁻] and osmolality (indicating osmoregulatory impairment), low glucose levels (likely limiting metabolic responses to maintain homeostasis) and high circulating cortisol levels (∼100 ng/mL). This suite of physiological disturbances is very similar to that observed in a condition referred to as ‘Winter Syndrome’ or ‘Winter Disease’ (WS/WD) in cultured gilthead sea bream (Sparus aurata) and other fish species. Thus, it appears that WS/WD described here for the first time in Atlantic salmon, alone or in combination with opportunistic infections, results in lipid deposition in the liver, compromising liver function and osmoregulatory capacity, and metabolic collapse that ultimately results in significant losses.

Although Lake Kanyaboli provides a sanctuary for fish species that are considered extinct (e.g., Oreochromis esculentus, Oreochromis variabilis and Haplochromis spp.) in Lake Victoria, comprehensive data on species diversity and abundance are lacking. This study, conducted over a year (February 2020 to February 2021), addressed this gap by assessing the temporal variation in fish diversity, abundance and catch (biomass) in Lake Kanyaboli. The primary fish data collected in the lake were supplemented with secondary data, and physico-chemical variables were used to correlate with fish assemblages. Fish catches decreased over time from 1981 to 2020, with the highest catch observed in 1981 (250 mt). Fish species composition data showed heterogeneity over the years, ranging from 9 to 15 species. O. esculentus, haplochromines, Oreochromis niloticus, Protopterus aethiopicus and Clarias sp. were present in all the reviewed years (from 1981 to 2020), whereas Coptodon zillii was non-existent post-1981 results. The February 2020 to February 2021 survey recorded 14 species dominated by Cichlidae (10 species), whereas Protopteridae and Anabantidae recorded one taxon each. Interestingly, Bagrus sp. was recorded in the current study, suggesting fish movement from the Yala River to the lake. The annual fish catch in the lake comprised tilapias (50%, O. esculentus, O. variabilis, O. niloticus and Oreochromis leucostictus), Clarias sp. (23%), P. aethiopicus (20%), haplochromines (7%), Cyprinids (0.03%) and Anabantidae (0.01%). There were no significant monthly differences in fish abundance and fish catches. The decline in fish catch in Lake Kanyaboli over the years is consistent with most tropical lakes and reservoirs in developing countries due to overexploitation. This study highlights the need for biomonitoring in Lake Kanyaboli to protect its fish population, including the endangered O. esculentus and O. variabilis, and ensure the long-term sustainability of the ecosystem.

The mass production of release-size H. scabra juveniles in the Philippines is primarily done in a floating hapa ocean-based nursery systems. To optimize its production, understanding the influence of different culture conditions and their management is necessary. In this study, the effects of hapa net cleaning interval, hapa layers, and stocking density on growth and survival of sandfish juveniles reared in floating hapa (L × W × H: 1.7 m × 0.9 m × 1.2 m) nursery system were assessed in two 60-day field studies. Results showed that the number of hapa net layers and cleaning interval had negligible effects on the growth performance of sandfish juveniles by day 30. However, sandfish juvenile survival was affected by hapa net layers with higher survival in triple-layer mosquito net hapas (40.5 ± 0.97%) compared to double-layer mosquito net hapas (17.8 ± 0.62%). By day 60, the growth performance of sandfish juveniles in double-layer hapas was higher (average weight: 5.0 ± 0.97 g; AGR: 0.13 ± 0.03 g day⁻¹) compared to that in triple-layer mosquito hapa nets (average weight: 3.1 ± 0.23 g; AGR: 0.07 ± 0.01 g day⁻¹). Survival of sandfish juveniles reared in double-layer mosquito net hapas, cleaned at 5-day intervals (85.9 ± 4.58%) was significantly lower compared to all other treatments. Conversely, initial juvenile stocking density did not significantly affect the growth performance and survival of sandfish juveniles in both rearing cycles. We therefore recommend the use of triple-layer mosquito net hapas during the first 30-day culture period and an initial stocking density of 1000 post-settled sandfish juveniles to increase production output. After 30 days, when the juveniles are larger, the use of double-layer mosquito net hapas and lower stocking density are recommended to reduce cost and enhance growth performance. Where cleaning is necessary, hapa nets may be cleaned at 10-day intervals to improve survival. The results of this study have important implications for optimizing the production of release-size sandfish in ocean-based nursery systems in the Philippines.

The present study was undertaken to evaluate the antioxidant and antimicrobial activity of chitosan-alginate-coated phycocyanin (PC) extract from Spirulina sp. on Penaeus semisulcatus infected with Salmonella typhimurium stored at 4°C and 8°C for 21 days. Four groups of shrimp treatments—a control sample (without infection and PC), an infected sample without PC, a non-infected sample + PC and an infected sample + PC—were used. The toxicity test revealed no toxicity of PC against Caenorhabditis elegans. The results of the pH, thiobarbituric acid, peroxide value (PV) and total volatile basic nitrogen showed that the lowest amounts of these factors were observed in the samples immersed in PC, whereas the highest values belonged to the samples infected with Salmonella. On the basis of the total number of bacteria in food (log 10⁷ CFU/g), the shelf life of shrimps treated with PC increased by 14 and 4 days at 4°C and 8°C, respectively, compared to the control. The diphenyl-2-picrylhydrazyl (DPPH) and ABTS results of the antioxidant activity indicated that the highest values were observed in the infected sample + PC after 21 days at 4°C and 8°C (82.65 ± 0.36 and 89.50 ± 0.43), respectively. The results of the colour assessment showed that the highest and lowest values belonged to the control sample (without infection and PC) and the non-infected sample with PC, respectively. The results of sensory analysis showed that the samples enriched with PC had a higher overall acceptability than samples without PC. In conclusion, PC increased the shelf life of shrimp infected with Salmonella sp.

Seaweed is multicellular marine macroalgae that enhances the immunity of aquatic organisms. The study was designed to assess the ethanolic extract (EtOH) extracted from red seaweed (Gracilariopsis lemaneiformis) on Nile tilapia (Oreochromis niloticus) to evaluate growth, immunity and haematological parameters. The EtOH was applied with fish feed in four treatments such as T1-control (0% EtOH), T2 (5% w/v EtOH), T3 (10% w/v EtOH) and T4 (15% w/v EtOH) each with three replicates. The initial average weight of the fish was 17.53 ± 2.1 g. Results showed that the growth increased gradually with the percentage of red seaweed extract, whereas the mean weight gain was found significantly higher in T4 (51.5 ± 4.2) than in the control. The specific growth rate (%) and survival rate (%) were found higher in T4 at the lowest FCR compared to other treatments (p < 0.05). The blood haemoglobin level of Nile tilapia was higher in T4 (11.5 g/dL) and lowest recorded in T1 (7.5 g/dL). However, the level of blood glucose interacted inversely with blood haemoglobin. The plasma protein level was also varied among the treatments (p > 0.05). The blood parameters, refractive index (RI) and spleen somatic index (SSI) were significantly different among the treatments. The RI of blood plasma and SSI were found to be better in T4 treatment. The research indicated that red seaweed extracts significantly enhanced the growth and boosted the immunity level of Nile tilapia.

Hydrilla verticillatata is an invasive aquatic macrophyte that has negatively impacted freshwater ecosystems in areas around the world. As a result, lake managers often seek ways to manage hydrilla and mitigate its spread. Having effective methods for assessing hydrilla abundance in a system is imperative, but traditional assessment methods are expensive, time consuming, and may be inaccurate. Contemporary remote sensing techniques have the potential to provide a faster and more effective means for obtaining hydrilla coverage estimates. Therefore, we set out to determine what methodologies provide the most efficient and effective approach for assessing hydrilla in a large reservoir. We used spectral indices on satellite imagery and unoccupied aerial vehicle (UAV) imagery to develop an image classification scheme for quantifying hydrilla occurrence. We also used down-scan sonar in conjunction with the BioBase software to generate hydrilla coverage and biovolume estimates. the normalized difference vegetation index derived from 3-m resolution multispectral satellite imagery proved effective for training an image classification, providing a reliable means at quantifying hydrilla colonization through time. The coloration index combined with UAV imagery yielded pixel values for hydrilla that were distinct from other aquatic plant species and can be used to verify results of satellite imagery. However, these methods were ineffective when hydrilla had not yet grown to maximum shoot length. In these conditions, down-scan sonar remained a valuable assessment tool to supplement aerial remote sensing techniques. These results equip lake managers with the knowledge to make more informed decisions, quickly assess hydrilla occurrence, and develop effective management strategies.