Aquaculture, Fish and Fisheries最新文献

Information on yellow perch Perca flavescens population dynamics and responses to various abiotic and biotic factors in oligotrophic, north-temperate inland lakes is limited. Water level fluctuations are known to influence available habitat and biological communities within the littoral zones of lakes, yet research is lacking for yellow perch in Wisconsin. The goal of our study was to characterize yellow perch population-level responses to natural water level fluctuations in four northern Wisconsin lakes using a 39-year time series. On average, increasing water level periods correlated with lower mean fyke net and gill net relative abundances (catch-per-unit-effort), though generally not statistically significant. Yellow perch mean relative weight varied among lakes and was significantly greater during increasing water level periods for all lakes except one. The lack of statistically significant findings potentially suggests a buffering mechanism of north-temperate oligotrophic lakes due to their small surface area to volume ratios, relative lack of nutrients, and(or) littoral structural habitat compared to other systems (e.g., shallow eutrophic lakes). Our results suggest that natural water level fluctuations may not be an environmental concern for yellow perch populations in some north-temperate oligotrophic inland lakes.

Fishery enhancement methods are being explored globally to sustain commercial and recreational fisheries through improving the productivity and management of marine populations impacted by anthropogenic stressors. It is expected that access to important Atlantic surfclam fishing grounds will be limited or lost due to growing overlap with offshore wind energy development. This study explores the economic viability of large-scale hatchery production to improve fishery access and potentially offset additional costs, reduced revenues and potential job losses associated with the displacement of the fishing fleet. Reports and primary literature were used to understand the growth and survival of Atlantic surfclams in hatchery and nursery settings to calculate the scale of hatchery efforts needed to support one million (1M) bushels of fishery-sized clams (>120 mm). Data on labour, energy, construction and material inputs and costs for hatchery and nursery production were gathered by analysing available literature and information provided by hatchery managers, researchers and others knowledgeable about shellfish hatchery production. A techno-economic cost model and Monte Carlo analyses were employed to explore average costs and their variability. This study suggests that 374M–2.1B Atlantic surfclams are needed at the end of the hatchery stage to produce 1M bushels of market-sized product. Total production costs range from $3.7 to $15.1M, including $2.9–$13.3M in hatchery costs and $800K–$1.9M in nursery costs. Under current market conditions, where Atlantic surfclams regularly sell for $14–$17/bushel, this analysis suggests that hatchery production could be considered a viable fishery enhancement method that supports human access to the fishery, though several additional questions remain.

Lake Victoria is the second-largest freshwater lake in the world, with a surface area of 68,800 km². The lake is rich in natural resources that are essential to the local economy and livelihoods. However, International Union for Conservation of Nature (IUCN) ranks 76% of freshwater species endemic to the Lake Victoria Basin as threatened with extinction. The biodiversity richness of the lake is still diminishing, and the risk of species extinction is increasing. Many species are yet to be identified, and thus the number of species threatened with extinction exceeds what is currently known. Furthermore, the lake is home to species that are found nowhere else on the planet, but its protection is never given the attention it needs. Genetic diversity loss is harmful to future populations and influences sustainability of the ecosystem. The decline in Lake Victoria's biodiversity is primarily attributed to various pressing issues, including water pollution, invasive species, climate change, overexploitation and the challenges stemming from high human population density. These problems are exacerbated by inadequate regulatory enforcement and a lack of comprehensive data and information to inform and guide conservation efforts. If these factors are not addressed, they may have a detrimental impact on Lake Biodiversity. This article aims to document the main threats to aquatic biodiversity as well as potential management strategies for preventing further losses of the aquatic biodiversity in Lake Victoria. The study recommends reviewing, bolstering and reinforcing the rules and regulations governing the extraction, accessibility and discharge of nutrients into the lake. The national governments should work with local governments, non-governmental organizations and local people to safeguard and conserve the lake's biodiversity. The national governments of the riparian nations should also reserve funds each fiscal year specifically for research that would inform effective management measures to prevent further losses of the lake's biodiversity.

Digestive enzyme activities are known to fluctuate in abalone grown under different environmental conditions however the effects of different dietary regimes are less clear. Therefore, in a 12-week study, the effects of water temperature and dietary protein levels on digestive enzyme activity in postweaned (6-month-old) greenlip abalone (Haliotis laevigata) were investigated. The abalone were fed diets with crude protein levels that ranged from 27% to 36% and cultured at 14°C, 17°C and 20°C. Diets were formulated to be isoenergetic (12.5 MJ kg⁻¹ digestible energy) and isolipidic (3.6% crude lipid). Trypsin, α-amylase and lipase activities were measured in the gastrointestinal region. Trypsin, α-amylase and lipase activities significantly increased as water temperatures were raised. In addition, significantly higher α-amylase activities were observed as protein levels increased, potentially indicating a compensatory effect to increase carbohydrate utilisation for energy metabolism when in short supply. However, abalone fed high dietary protein levels may also utilise protein for energy metabolism. Further research investigating the dietary carbohydrate source for greenlip abalone is recommended. This study provides useful information on the digestive enzyme activity in postweaned greenlip abalone to improve diet strategies for sustainable production.

Abbreviated abstract: Post-weaned greenlip abalone digestive enzyme activity was examined after feeding four dietary protein levels at three different temperatures for a 12-week period. Enzyme activities were significantly increased with increasing water temperature. Additionally, significantly higher α-amylase activities were observed as protein levels increased.

The nutritional condition of seed mussels (spat) at the time of seeding is thought to play a major role in influencing spat losses on mussel farms, with nutritionally compromised spat thought to be more likely to be lost from aquaculture substrata than those in good condition. New Zealand's Greenshell^™ mussel (Perna canaliculus) aquaculture industry relies almost exclusively (∼85%) on wild caught spat, with the vast majority, typically > 90%, lost shortly after being seeded onto coastal mussel farms. This study sought to quantify the extent of the variability in the nutritional condition (i.e., calorific, protein, lipid and carbohydrate content) of samples of spat used by the Greenshell^™ industry between 2014 and 2021 (i.e., wild caught and hatchery produced) as a first step towards determining whether variability in nutritional condition may be a significant contributor to the marked variation observed in spat performance after it is seeded onto coastal farms. All parameters measured were highly variable among wild spat samples, with all but lipid content varying, including for samples of wild spat harvested at different times within the same month. Furthermore, there were no clear patterns in the nutritional condition of spat across months or years, suggesting environmental factors that limit feeding during the harvest and transport of spat may be contributing to marked differences in the quality of spat being used by the industry to seed farms. These results provide a baseline for assessing the nutritional condition of Greenshell^™ spat and point towards a need to develop interventions to improve the quality of wild spat supply for this industry to help and prevent the ongoing massive losses of spat from farms. These measures could include, testing nutritional condition of spat at harvest or prior to seeding, development of nursery culture methods and development of artificial spat feeds that have the potential to replace live phytoplankton during nursery culture.

Freshwater aquaculture can have negative impacts on chemical, physical and biological water quality. To contextualise the impact that these activities may have, a case study site in Ireland was monitored for 1 year. The study aims were to investigate the impact of freshwater aquaculture on water quality (biological, physical, and chemical) and the degree of the impact and recovery in water quality, within 1000 m downstream of a salmon smolt hatchery. The hatchery was monitored, at four locations (upstream, 10, 100, and 1,000 m downstream of the discharge point). Data on macroinvertebrate, macrophyte, hydromorphology and chemical characteristics were collected. Results for the physical monitoring indicated no significant changes in hydromorphology between up and downstream sites. Chemical water quality did decrease downstream in terms of nitrogen (N) and phosphorus (P). The greatest concentrations in N and P were found at 1000 m though it is likely additional contributions from agriculture impacted this site. Dissolved oxygen was steady throughout the monitoring campaign with a 13% variance between upstream and downstream locations. Changes in biological indices were statistically significant for taxa at all downstream sites. There were positive trends which indicated a degree of recovery in biotic indices.

Rainbow trout (Oncorhynchus mykiss) is among the most widely translocated fish species in the world. The current study evaluated the spawning interactions between naturalized and wild rainbow trout from two high-altitude second-order streams, in Kenya. Data on total length, weight, condition factor, fecundity, fertilization, egg diameter and fry survival were collected on spawning rainbow trout between March and December 2021. Length–weight relationship showed parabolic equations as W = 0.0144L^2.900, W = 0.0069L^3.0285 and W = 0.00027L^3.175 for wild fish stock, hatchery-reared and wild × hatchery-reared rainbow trout, respectively. Total fecundity differed significantly among the hatchery-reared, wild fish and the cross of the two (p < 0.05). The fertilization rate showed significant differences (p < 0.05), with no discernable difference observed between the hatchery-reared and crossed (wild × hatchery-reared). There was a positive correlation among the total fecundity to female egg weight, female body weight, fertilization rate and eyed egg survival in all the populations. Relative fecundity was significantly different among the three groups of fish (p < 0.05), but the differences between the hatchery and the crossed (wild × hatchery-reared) fish showed no significant differences. We recommend the use of crossed (wild × hatchery-reared) populations for fry production for use in aquaculture as they presented the highest fecundity and gave the best outcome of fry with high survival.

Poor and unreliable knowledge of the status of freshwater fisheries limits their inclusion in governance processes, thereby impeding effective management measures. This threatens the livelihoods of people, particularly in developing countries. Improved knowledge is required to draw the attention of policymakers and stimulate effective management measures to accelerate the sustainability of the freshwater fisheries. In line with this requirement, this paper provides the state of knowledge of the aquatic ecosystem and fisheries of the Lake Edward system, East Africa, focusing on lakes Edward, George and the Kazinga channel. The state of knowledge was accomplished by reviewing existing data and information on aspects of primary productivity and water quality, invertebrates, fish fauna, fish life history and ecology, and fisheries. The waterbodies have been monitored since the 1930s, albeit sporadically, providing data on all the above aspects but with substantial temporal gaps. Adequate and updated data and information exist on the water quality status of the water bodies, extant aquatic taxa (including fishes) and fish catches but with uncertainties in the latter. Data and information gaps exist on the abundance of biotic communities, fish life history, quantitative trophic ecology and fisheries management reference points. The aggregated data and information can directly support decisions for fisheries management. We recommend regular monitoring to fill the data and information gaps, more comprehensive stock assessments and the development of aquatic ecosystem models.

Stagnating capture fisheries and increasing fish protein demand necessitate aquaculture production to bridge the gap. Lake Victoria is a potential water body for increasing fish production through cage farming. The sustainability of Lake Victoria for cage farming depends on timely and holistic site selection. However, current site selection methods involve complex, resource-intensive field surveys that lack a holistic approach to integrate multiple factors. Accordingly, information regarding suitable sites for sustainable fish cage farming in Lake Victoria remains scarce. In this study, a transparent geographic information systems (GIS) and multicriteria evaluation (MCE) here after reffered to as GIS-MCE was used to reveal potential sites to be permitted or avoided during cage aquaculture development in the Mwanza Gulf of Lake Victoria (Tanzania). Our analysis involved weighting and integration of sub-models representing ecologically sensitive areas, physical environment, and socio-economic and water quality variables into a single spatial model portraying different site suitability levels in the Mwanza Gulf. The results indicated that the sub-models identified relatively larger suitable and most suitable sites compared to the overall model. No site maintained its status across all sub-models. The overall model designated a small area (5.10 km² or 1.52%) as the most suitable site, with 24.20 km² (7.44%) as suitable, 64.47 km² (19.82%) as less suitable, and 42.63 km² (13.12%) as unsuitable for cage fish farming. The remaining area (188.84 km² or 58.06%) was a constrained site to be avoided during cage aquaculture development. Taken together, the individual sub-models are ineffective in designating potential sites for fish cage culture and thus should not be used solely. The GIS-MCE general model provides a fast and timely method for identifying potential sites for cage farming in Lake Victoria. Fish farmers and managers should use the GIS-MCE overall model in inland waters to facilitate site selection for complying with licensing requirements and decrease field extensive surveys.

To allow sea urchin aquaculture to achieve its intended scale, efficient and precise methods for measuring large numbers of urchins in commercial-scale operations are needed. Current protocols for measuring urchin test (shell) dimensions and mass are time-consuming and prone to high measurement error, thus inconvenient in research and impractical in a commercial context. This study investigates and compares various measurement methods with a newly developed computer vision approach developed in this study, to establish a single protocol using precise, efficient and accessible methodology for measuring live urchins. We show that urchin wet mass can vary up to 8.73% depending on time out of water; this is significantly reduced to an average of 0.1% change by allowing urchins to drip-dry for at least 90 s prior to weighing. We found the conventional vernier calliper method used to measure urchin dimensions to be both time-consuming and imprecise (mean coefficient of variation (CV) of 2.41% for Tripneustes gratilla). Conversely, the computer vision programme we developed measures with higher precision (mean CV of 1.55% for T. gratilla) and is considerably faster. The software uses a series of hue saturation value filters, edge detection algorithms and distortions to measure the diameter of the test (excluding spines) of multiple urchins at once. The software is open-source, and the protocol does not require specialised equipment (can be performed with a mobile phone camera). When the computer vision application is combined with the simple procedures described in this paper, to reduce measurement inaccuracies, urchin wet mass and diameter can be more efficiently and precisely determined. For a larger scale context, this software could easily be incorporated into various tools, such as a grading machine, to completely automate various farm processes. As such, this study has potential to assist urchin data collection in both research and commercial contexts.