Aquaculture, Fish and Fisheries最新文献

This study was carried out along the Mwanza Gulf, Lake Victoria, Tanzania, where water samples for the determination of physico-chemical parameters were collected from March to October 2023. NH⁴⁺-N, NO³⁻-N, NO²⁻-N, and PO⁴⁺-P were analyzed using standard methods. Temperature (°C), electrical conductivity (µS/cm), dissolved oxygen (mg/L), pH, and turbidity were measured in situ. Water temperature ranged from 27.9°C at Misungwi to 29.1°C at Nyamagana. Dissolved oxygen (DO) was high at Ilemela (6.70 mg/L) and declined (5.78 mg/L) at Nyamagana. Electrical conductivity and water turbidity increased as the number of cages sampled increased. Nitrate increased from 0.09 mg/L (90 µg/L) at Ilemela to 0.15 mg/L (150 µg/L) at Nyamagana, ammonia concentration from 0.26 mg/L (260 µg/L) to 0.45 mg/L (450 µg/L) at Nyamagana, and phosphate increased from 0.26 mg/L (260 µg/L) to 1.41 mg/L (1410 µg/L). When the results of this study were compared to those reported before 2015, the variations were significant at all levels. We conclude that inputs from cage fish farming are contributing immensely to nutrients loading and thus pollution in the lake. The riparian governments around the lake are urged to take measures that will ensure sustainable cage fish farming without jeopardizing the environmental quality of Lake Victoria with the consequential collapse of the existing fishery.

Preventing the spread of aquatic invasive species, such as non-native molluscs, plants, and fish, hinges on early detection to help managers avoid establishment. Here, we evaluated two detection methods for a prolific invader: dreissenid mussels. We compared environmental DNA (eDNA) testing to cross-polarized light microscopy detection (CPLM) of dreissenid larvae (veligers). Microscopy is widely used for dreissenid detection, whereas eDNA testing is not yet common. We analysed 85 samples collected from July 2014 to September 2015 from two water bodies in Minnesota with known infestations of zebra mussels (Dreissena polymorpha), and one water body (Duluth/Superior Harbour in Lake Superior) that is infested with both zebra and quagga mussels (Dreissena rostriformis). Using a probe-based quantitative PCR eDNA assay, we detected Dreissena eDNA in 34 of the 62 veliger-negative samples and 11 of the veliger-positive samples, whereas eDNA was not detected in 12 of the veliger positive samples. Our results suggest managers and researchers could improve early detection sensitivity by using eDNA testing of plankton tow-net sampling to complement microscopy detection of invasive bivalves. eDNA technologies, including large-volume tow-net sampling (with or without veligers present in the waterbody), can help prevent false negative detection outcomes and improve early detection of invasive mussel species.

Is there an ecological niche for ‘ocean ranched’ hatchery salmon, Oncorhynchus spp., to supplement wild salmon? Ecologically, I hypothesize that the carrying capacity for biota is: (1) limited; (2) filled with locally adapted biota competing and cooperating to nurture viable offspring; and (3) sustained by the biogeochemical recycling of their nutrient elements. Thus, biotic abundance is limited more by the space and food needed to nurture viable adults than by the numbers reproduced. Hatchery immigrants compete for space and food with wild biota, spawn with and reduce the fitness and biodiversity of wild salmon, and their growth and commercial harvest consume more biogeochemical resources than they recycle. This contributes directly to ecological overshoot and to the declining or depressed populations of wild salmon, Pacific herring Clupea pallasi and eulachon Thaleichthys pacificus now observed in Southeast Alaska and wherever there are production releases of hatchery salmon. Industrial-scale hatcheries do not have a niche in sustainable salmon management.

The aim of this study was to investigate the effects of Coccomyxa sp. on the survival, nutritional profile, pigments and digestive enzyme activities of Mystus gulio. A 75-day feeding trial was performed during which the fish fry were fed with microalgae as a partial replacement for other nutritional components. The fry were fed five different diets: a commercial feed, a control diet without Coccomyxa sp. and three experimental diets incorporating Coccomyxa sp. at varying rates of T1 (5% inclusion), T2 (10% inclusion) and T3 (15% inclusion). Fry (35 per tank) were cultured in triplicate 35 L glass tanks and fed twice a day at 5% of their body weight. The findings showed that among the treatment groups, T3 had the highest survival rate (81% ± 4.36%), followed by T1, T2, control and commercial. Furthermore, T3 had the highest quantities of protein (43.8% ± 6.55% dry weight) and lipids (25.9% ± 0.68% dry weight), whereas T2 had higher amounts of carbohydrate (14.9% ± 1.99% dry weight). Meanwhile, the polyunsaturated fatty acid (PUFA) content varied significantly (p < 0.05) among the treatments, whereas T3 was the highest (41.75 ± 0.12 ppm). Additionally, it was also found that the T3 group exhibited higher carotenoid and astaxanthin content in the fish body. Moreover, the T2 diet resulted in higher levels of amylase (13.7 ± 0.16 U/g) compared to the other diets. Conversely, protease (12.6 ± 0.15 U/g) and lipase (2.20 ± 0.13 U/g) activity were found greater in T3 treatment. These results suggest that microalgae can be used as a viable and alternative feed ingredient in aquaculture diets.

Cage fish farming has emerged as a key component of aquaculture in Lake Victoria, Kenya, providing critical contributions to food security, employment and local livelihoods. Despite its growth, the sector faces recurring challenges—including inadequate regulatory compliance, poor environmental management and frequent mass fish kills that threaten its long-term sustainability. Notably, there is a lack of empirical data and structured analyses on the economic consequences of these fish kills and the extent of non-compliance with statutory regulations. The mass fish kills that occurred in November 2022 in Kisumu and Homa Bay counties highlighted these systemic vulnerabilities, resulting in significant financial losses and ecological disruptions. This study addresses this critical gap by assessing the socio-economic impacts and governance shortcomings associated with fish kills in Lake Victoria's cage aquaculture. Specifically, the study quantifies economic losses, evaluates regulatory compliance among affected farms and proposes actionable recommendations to enhance sustainability and resilience in the sector. A mixed-methods approach was employed, involving surveys, stakeholder interviews and field observations across 10 affected beaches. The study found that fish kills led to total economic losses of $7.7 million, with Kisumu County incurring 95.35% of the losses. High-density cage farms, particularly at Ogal, experienced severe losses due to overcrowding, degraded water quality and nutrient accumulation. Harmful algal blooms exacerbated these conditions, leading to widespread fish mortality. Male-owned farms bore the largest financial burden, reflecting their dominance in the sector. The lack of compliance with statutory licensing requirements further amplified vulnerabilities. Inadequate governance, poor environmental management and limited farmer training are critical threats to cage aquaculture sustainability. Therefore, strengthening regulatory frameworks, promoting environmental monitoring and enhancing farmer capacity through training are recommended. Additionally, integrating Beach Management Units (BMUs) into formal governance frameworks and supporting cooperative farming models could enhance fish health resilience.

The impact of climate change on aquaculture threatens global food security, disrupting fish productivity and sector sustainability. Climate-smart aquaculture (CSAq) offers a viable strategy to mitigate these challenges, particularly during droughts, through practices such as adjusted fish stocking, dam lining, tanks, boreholes and pond covers. Despite their benefits, adoption among smallholder fish farmers in Kakamega County remains low. This study examines factors influencing CSAq adoption among 220 smallholder fish farmers, selected through a multistage sampling technique. A multivariate probit model was employed to analyse the data. Results indicate that farming experience, gender, education level, age, land ownership, household size, extension service frequency and access to CSAq training significantly influence the adoption of these practices. Farmers with more experience, higher education and greater access to training and extension services were more likely to implement CSAq techniques. The findings highlight the need for targeted interventions to enhance CSAq adoption. Policies promoting knowledge dissemination, improved farmer training and increased access to extension services are crucial for strengthening climate resilience in aquaculture. Investment in these areas will encourage smallholder farmers to adopt CSAq practices, ensuring sustainable fish production and long-term sector stability amid climate change challenges.

Saccharina japonica is a cold-water macroalga mainly distributed in the coastal areas of the North Pacific Ocean and the Atlantic Ocean, and it is one of the seaweed varieties with the largest culture production in the world. S. japonica cultivation plays a pivotal role in the aquaculture industry of China's coastal provinces. In recent decades, China's S. japonica production has steadily increased, and the country has become the largest producer and exporter of S. japonica in the world. This paper presents in detail the development status of China's S. japonica industry from the aspects of S. japonica varieties, main production areas, culture production and area, seedings, processing, brands, import and export trade, culture models and disease. The paper further discusses the challenges faced in the development of China's S. japonica industry and proposes a series of strategic solutions to foster its sustainable growth. These efforts aim to provide Chinese experiences and viable strategies for other S. japonica farming countries in the world.

Designing aquatic nest boxes is rarely afforded detailed scientific account. Here we provide some historical context for nest boxes used in production of large-bodied fishes of the Australian freshwater cod genus Maccullochella. Our experience with eastern freshwater cod is used as a case study to: (a) convey aspects of the complexity of the nest box design process and to (b) demonstrate the importance of visual literacy in project communication across the variety of contributors to the eco-design process. Specifically, we describe a new, two-variant, triangular nest box design for application in rivers and modifications to a standard stainless steel nest box for hatchery-pond-based spawning of eastern freshwater cod M. ikei. We designed the boxes to test adult preference for single versus double entrance/exits to cavities in hatchery and field environments. An important consideration specific to hatchery production is harvesting demersal, adhesive eggs prior to hatching to minimise fungal infection of eggs and physical loss of larvae, in addition to providing critical first feeding of larvae. In contrast, field nest box design incorporated multiple factors and associated trade-offs related to both internal and external design, ranging from manufacturer capability, material types, cost, transportability, hydrological performance, biodegradability, retrievability, as well as biological and ecological function. Only preliminary findings from field nest box deployments are provided here, and we focus primarily on elements of visual language in the form of conceptual drawings, sketches and final schematics which have been central to our process. We emphasise the benefit of harnessing input from multiple fields of expertise and documenting and testing designs of nest boxes for cavity nesting fishes, under both controlled hatchery and more complex field conditions.

Cage fish farming, a recent development in aquaculture, has enhanced fisheries production due to its higher stocking densities than traditional pond and open-water systems. Although it can enhance production, the system can pose biodiversity threats when there is an unintentional or intentional release of stocked fish into the wild. In this review, we examine the expansion of Nile tilapia (Oreochromis niloticus L.) cage aquaculture in Africa and the potential threats that this may have on congeneric Oreochromis species. Threats such as interspecific competition, disease transmission and hybridisation, which are drivers of genetic diversity loss among native fish populations, have been reported. However, most studies have focused on investigating cage fish production, water quality and the associated economics, but research assessing the genetic and ecological impacts imposed by the escaped fish from cages on native species is still limited across African countries. While direct evidence of hybridisation due to cage fish farming is lacking, genetic mixing of Nile tilapia with native Oreochromis species has been reported in some African water bodies. Further, only Egypt, Kenya and Uganda have functional Fisheries and Aquaculture regulations for guiding the aquaculture activities. Thus, there is an urgent need to institute regulatory frameworks that not only provide clear guidelines on aquaculture production but also balance between environmental conservation and economic sustainability.