Aquaculture, Fish and Fisheries最新文献

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.

The present study provides a comprehensive analysis of the population structure (length–frequency distributions), growth pattern (length–weight relationships [LWRs] and length–length relationships), physiological condition factors (allometric [K_A], Fulton's [K_F] and relative [K_R]), relative weight (W_R) and form factor (a_3.0) of Chanda nama. A total of 1200 specimens were collected from the Old Brahmaputra River, northeastern Bangladesh, for 12 months by traditional fishing gear, including seine net and cast net. The total length (TL) of several individuals varied from 2.3 to 7.2 cm. The highest percentage contributed to the population's 4.0–4.5-cm-sized group. The LWRs indicated a positive allometric growth pattern (b > 3.0). Fulton's condition factor significantly correlated with TL and body weight (p < 0.0001). The calculated W_R ranged from 67.38 to 137.64. No significant variations from 100 were found using the Wilcoxon rank test (p = 0.034), suggesting that C. nama might live there in a balanced predator–prey environment. Furthermore, the measured value for the form factor (a_3.0) was 0.0105. In addition, fish with a TL of 7–8 cm should be caught since they are in good condition and have enough meat. The study's findings will greatly contribute to the efficient and enduring management of C. nama in the Old Brahmaputra River and its adjacent ecosystems.

Expansion of pearl production using the silver-lip pearl oyster, Pinctada maxima, depends on increasing the availability of high-quality spat from hatcheries and optimization of existing hatchery protocols. Research to develop feeding regimes yielding higher quality spat is seen as a priority. This study evaluated the suitability of three microalgae (Rebecca salina, Chaetoceros simplex and Tisochrysis lutea), fed singly and in combination, for spat of P. maxima and assessed whether mixed diets yielded spat of higher quality. A model-fitting approach examined the response of spat fed microalgal diets for 35 days. Organic content of spat, as an indicator of quality, as well as metrics relating to spat size and weight were considered. On the basis of organic content, all microalgal diets tested were found suitable and there was no evidence that the mixed diets yielded higher quality spat compared to monospecific diets. Further, any gains in spat size attributed to the mixed microalgal diets were comparatively modest. Contrary to long-held assumptions, our results indicate that monospecific microalgal diets are not necessarily inferior to mixed microalgal diets for on-growing spat of P. maxima. They indicate potential to develop simpler and cheaper protocols for culture of P. maxima spat in land-based systems.

The cover image is based on the Article Toxic Effects of Tributyltin, Triphenyltin, and SnCl₂ on the Development of Zebrafish (Danio rerio) Embryos by Aref Barkhordari et al., https://doi.org/10.1002/aff2.70005.