Aquaculture, Fish and Fisheries最新文献

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.

Growing seed mussels (spat) to larger sizes in single-seed nursery culture systems prior to seeding onto coastal mussel farms is an effective approach for greatly reducing costly spat losses during this stage of mussel aquaculture. However, the production of single-seed mussel spat in nursery culture systems relies on first separating spat from the settlement substrata to which they are attached, whether spat are settled in a hatchery or gathered from the wild. This study sought to determine whether chlorination could be an effective approach for separating wild Greenshell mussel (Perna canaliculus) spat from beachcast macroalgal material (Kaitaia spat material) harvested from a beach in northern New Zealand. The results demonstrate that chlorination (i.e. in solutions of up to 0.625% sodium hypochlorite) is a highly effective approach for separating spat, resulting in the detachment of up to 94.6% in one treatment without increasing mortality relative to controls. The effectiveness of chlorination was modulated by spat density, with increasing spat densities, lowering rates of detachment. While chlorination is effective at separating small spat (i.e. successfully separating 72.4% of spat <750 μm in shell length) overall spat densities, further investigation is required to determine how to effectively separate larger spat (i.e. with chlorination only successfully separating 21.5% of spat >750 μm). The high survival (relative to the control treatments) also suggests that chlorine concentrations and exposure durations could be increased from those used in this study. These results demonstrate that chlorination can be used to separate spat from substrate prior to their transfer to nursery systems for ongrowing, paving the way for such approaches for reducing spat losses to be integrated into the aquaculture production cycle.

Aquaculture developmental plans represent a nation's determination for self-reliance on domestic fish production through resilient aquaculture. This study reviewed the 2012 Ghana National Aquaculture Development Plan (GNADP) and sought inputs from industry stakeholders to inform GNADP 2023 using the ecosystem approach to aquaculture (EAA). In furtherance of this, we also investigated the justifications for antibiotic treatments including the assessment of the sector that is supposed to regulate aquaculture growth. The findings suggest that GNADP 2023 must be strategized to address industry sustainability bottlenecks identified as input availability and quality, permitting, regulation and enforcement, financing schemes and technical expertise. In terms of technical expertise, the inclusion of women in aquaculture can diversify the skill sets for the improvement of capacity and competence in good aquaculture practices and fish health management. Sector partnerships can aid in leveraging the expertise and resources among sectors to address persistent industry issues. The justifications for antibiotic treatments are disease management, prophylactics, antibiotic availability, application, and effectiveness, capacity and competence, including regulation and enforcement. This also comprised the sense of ownership and responsibility as farmers feel they must safeguard their investment. It is therefore important for farmers to pursue preventative aquaculture biosecurity measures. The government sector was selected predominantly to regulate aquaculture growth. We however recommended a participatory approach as this could facilitate peer regulation to enhance the regulation and enforcement of aquaculture regulations. The findings in this study are worth considering as it pioneers the adoption of the EAA framework for aquaculture developmental planning in Ghana.

Drift by larval white sturgeon (Acipenser transmontanus) results in an ontological habitat shift during early life that may be influenced by changes in the trade-off between mortality risk and growth potential. Despite the importance of early life history to recruitment and conservation, for many species, including white sturgeon, we have a limited understanding of the mechanistic drivers of drift. We tested if two biotic factors, conspecific density and timing of food availability during the yolksac larvae stage, influenced the timing of drift behaviour. We evaluated larval drift timing for yolksac larvae reared in laboratory mesocosms at two densities (10 or 20 larvae) and three feeding initiation times (before exogenous feeding, at the initiation of exogenous feeding, or starvation). We found that drift occurred at 13 days post-hatch (dph) overall, 2 days after the shift from the yolksac stage to the feeding stage (11 dph at 14°C). The timing of food availability in the fed treatments did not affect the timing of larval drift, nor did the density of conspecifics. Starvation delayed drift timing by 2 days, to15 dph. This delay of drift from a habitat with no food availability may disadvantage starving larvae and reduce growth potential.

We evaluated the effect of probiotics on the growth and culture condition of rotifer in medium-sized culture tanks. The influence of probiotics on the changes in swimming patterns, velocity and sinuosity indices of rotifer was also examined. The rotifers (Brachionus rotundiformis) were cultured for 14 days in nine polycarbonate tanks containing seawater which were divided into three groups: a control group (Chlorella product) and two treatment groups: Chlorella + Probiotic I and Chlorella + Probiotic II. The rotifer population and the water quality parameters were monitored daily. To evaluate the locomotory behaviour of the rotifer, a sub-sample containing rotifers was obtained from each treatment and placed on a glass-bottomed dish. A high-speed camera mounted on a stereo microscope was used to record the rotifer movement. The footage was then analysed using motion analysis software to establish the swimming velocity, swimming pattern and sinuosity indices of the rotifers. Co-feeding rotifer on microalgae and probiotics resulted in a higher rotifer growth rate (0.51 ± 0.03) and decreased concentration of unionized ammonia (0.14 ± 0.02 mg L⁻¹). In addition, the probiotic-fed rotifers had 1.59 times higher average swimming velocity (0.97 ± 0.11 mm s⁻¹) and more straight swimming pattern compared to rotifers that fed on microalgae alone whose velocity was slow (0.61 ± 0.14 mm s⁻¹) and more sinuous. From these data, we can postulate that probiotics have the potential to attenuate rotifer culture conditions by decreasing ammonia concentration as well as influence rotifer swimming behaviour which could affect rotifer reproduction and the quality of fish larvae in aquaculture systems.

A novel general model has been developed to fit biomass growth data of coleoid cephalopods as a function of time and temperature from hatching to maximum size in a single curve. This model has been obtained formally from a formulation of product-integral, solves the discontinuity problem present in two-phase growth models and describes both asymptotic and non-asymptotic growth. Within the usual temperature range in which the organism develops, our model describes a non-asymptotic growth achieving a good fit with the experimental data $��\left(��R^2�>�0.98��\right)�$. In particular, the model provides precise calculation of the time k at which the growth curve inflection occurs, time μ₁ at which sexual maturity begins and time μ₂ at which the maximum size is reached. When the model was parameterized as a function of temperature, it corroborated different results on Octopus maya fitness, in particular, 25.7°C was obtained as the temperature that generates the highest average growth rate and 21.7°C as the temperature with the highest biomass accumulation over time. This result confirms that the temperature range of 22–26°C is suitable for the growth of O. maya and shows that the developed model can be a useful tool for aquaculture.

This study examined factors affecting fishers' interest in participating in human immunodeficiency virus (HIV) testing at Elmina fishing community in the Central Region of Ghana. The study additionally inquired of respondents if they would be willing to submit to an HIV test and, if so, if they knew where to go for the test. The study also looked at the barriers that prevented fishers from getting tested for HIV. A cross-sectional convergent parallel mixed-method design was used to examine 385 fishers who were at least 18 years old and engaged in any form of fishing activity. Only about 9% of respondents reported having ever tested for HIV. Although the overall testing rate was low, the results indicate a higher testing rate in females than among males. Multivariate analysis shows that sex, age and type of fishing occupation are significant predictors of willingness to test for HIV among the study participants. Even though many people in the study location may know where to get tested for HIV, they are unwilling to do so. Many residents of the research area may be aware of where to get tested for HIV, but they are unwilling to go. This suggests a lack of enthusiasm due to misunderstandings and misconceptions about what HIV testing uptake entails. Additionally, stigmatization is a significant barrier to the acceptance of HIV testing in the study area and needs to be reduced by increased education.

Although small-scale fisheries and aquaculture provide opportunities to increase fish yield to supplement rural food and income, they remain undeveloped in Ghana. To contribute towards the development of the sectors, this study sought to assess the biology and ecology of Oreochromis niloticus and Sarotherodon melanotheron in the Brimsu reservoir to provide the requisite information for their management. From the results, mean temperature, dissolved oxygen, pH and transparency of the reservoir were 30.03 ± 0.27°C, 3.78 ± 0.38 mg/L, 8.30 ± 0.21 and 69.79 ± 1.76 cm, respectively. S. melanotheron had a sex ratio of 1:1.36; with mean condition factors of 2.177 ± 0.089 and 2.06 ± 0.029 (p = 0.08) for males and females, respectively. The sex ratio of O. niloticus was 1.45: 1; with mean condition factors of 2.208 ± 0.012 and 2.257 ± 0.014 (p = 0.07) for males and females, respectively. Both species exhibited positive allometric growth with no significant differences between the condition factors for males and females. In addition, there was no significant difference between the sex ratios for S. melanotheron but the number of males of O. niloticus was significantly higher than the females (p ˂ 0.05). Size at sexual maturity (L_m), form factor (a_3.0), growth coefficient (K), asymptotic length (L_∞) and natural mortality (M) of S. melanotheron were 18.00 cm, 0.020, 0.42 year⁻¹, 30.32 cm and 0.64 year⁻¹, respectively. For O. niloticus L_m, a_3.0, K, L_∞ and M were 18.57 cm, 0.0223, 0.26 year⁻¹, 38.42 cm and 0.41 year⁻¹, respectively. However, the catch per unit effort for O. niloticus was higher than that of S. melanotheron throughout the study period. The conditions of the reservoir were favourable for the growth of these cichlids. It is recommended that measures should be put in place for the sustainable management and exploitation of fish stocks.

Fisheries systems face enormous pressures from increased fish demand, decreased fish catches, and an ageing fishing population. As a case study, we investigate how climate change stressors, capacity-building opportunities, and the introduction of climate-smart innovations, tools and information may influence youths’ succession decisions in small-scale fisheries (SSF). We collected empirical data from a survey with the children of SSF actors to identify the factors promoting or hindering succession in fish harvesting activities through a simple random sampling of 415 youths in six fishing communities in Cameroon. The probit model results revealed that youth participation and succession decisions are positively influenced by their education, nationality, that is, being a migrant, desire to be employed full-time in fisheries-related activities, climate-smart innovations, tools and information, and capacity-building opportunities. Increasing temperatures and uncertainty in fish availability due to climate change negatively influence their succession decisions. We find that parents do not encourage their children to participate in SSF due to climate change impacts, which are reducing fish catch and due to a lack of suitable climate-resilient innovations and capacity-building opportunities. The study provides evidence that interventions that create an enabling environment for youths’ participation in fisheries-related activities are important to secure the future of SSF in Cameroon.