Aquaculture Management Practices Research Articles

61 A Multifaceted Approach to Improving Fish Farming in Kenya’s Lake Victoria Region

OBJECTIVES/GOALS: This project adopts a multifaceted approach to improving aquaculture management practices in Kenya’s Lake Victoria region by identifying fish pathogens, measuring algal toxin levels in commonly consumed fish, surveying fish farming practices, and educating the public. METHODS/STUDY POPULATION: Limited existing data on the state of floating cage culture in Kenya influenced our decision to begin this portion of the project with a brief literature review of potential Nile tilapia pathogens. Databases were screened for mention of disease in either wild or caged Nile tilapia, with emphasis given to those in Lake Victoria. Results were compiled into a spreadsheet and analyzed for frequently occurring pathogens. The next portion involved creating an interview style survey to assess current cage culture management practices in the region. Editing was done to ensure questions remained unbiased, non-leading, culturally sensitive, multilingual and relevant to the situation. Data went through a quality control screening and analysis was conducted through the R programming language. RESULTS/ANTICIPATED RESULTS: Beginning with mortality, of the 93 farms surveyed, data analysis revealed that there is a higher probability that farms will have a mortality of approximately 20%, over the course of a production cycle. For biosecurity and fish health practices, data shows that 97% of farms do not disinfect scooping nets or other fish handling materials when moving from one cage to another. During the 2022-2023 production cycle, 44% of farms experienced fish kills of over 50 fish. 73% of the 93 farms do not contact any organization when a fish kill occurs. In a qualitative answer, it also appears that many farm workers dispose of their dead fish within the lake, feed it to livestock or dogs, or eat it. Algae blooms have been experienced at 80% of the farms surveyed and 43% of farms say they have seen fish gasping at the surface for air. DISCUSSION/SIGNIFICANCE: While farms are implementing good management practices in the areas of cage design, stocking, and feeding practices, there is room for improvement in fish health, biosecurity, and managing algal blooms. The findings provide insight into the areas that should be considered when taking action to improve the welfare of the region.

Enhancing aquaculture management: Utilizing cu-doped ZnO/graphene nanocomposite for effective reduction of antibiotics and antibiotic-resistant Bacteria in shrimp culturing ponds

Shrimp culturing ponds, and enclosed breeding environments, contribute to the dissemination of antibiotics and antibiotic-resistant bacteria (ARBs) in aquatic ecosystems. This study focuses on the synthesis of a ternary nanocomposite photocatalyst, comprising Cu-doped ZnO and reduced graphene oxide (GP), using a one-step microwave-assisted hydrothermal method. The photocatalyst was employed to effectively eliminate antibiotics and inactive ARBs from aquaculture water. The structure, morphologies, and optical properties of the synthesized composites were investigated. Tetracycline (TET) and florfenicol (FLO) were the most frequently detected antibiotics in shrimp pond water, followed by sulfamethoxazole and tiamulin. Photo-degradation efficiency of TET and FLO using composite significantly improved under both UV and simulated solar irradiation. After 60 and 180 min of irradiation, the removal percentages for TET were 87.5% and 80.3%, while for FLO they were 89.5% and 92.1% respectively. The Cu-ZnO/GP composite demonstrates potent antibacterial activity against both Gram-positive (E. faecalis V583) and Gram-negative (E. coli K12 MG1655) antibiotic-resistant strains under light exposure. Its photocatalytic properties augment reactive oxygen species (ROS) generation, thereby enhancing bacterial inhibition. After 24 h of light exposure, E. coli growth was inhibited by 78%, while E. faecium growth was suppressed by 92%. The composite achieved the highest inactivation levels for E. coli (Ln-3.8) and E. faecalis (Ln-2.8) after 15 min of light exposure. The efficacy of Cu-ZnO/GP composite treatments in bacterial inactivation was notable in both ultrapure water (UPW) and real wastewater (RWW) matrices, achieving significant inactivation levels after a 1-h treatment. These findings underscore the potential of Cu-ZnO/GP composites to improve aquaculture management practices, thereby mitigating antibiotic proliferation in aquaculture waters and the surrounding environment.

Investigating Aquaculture Management Practices and Challenges in Selective Aquaculture Hatcheries Across Khyber Pakhtunkhwa, Pakistan

Investigating Aquaculture Management Practices and Challenges in Selective Aquaculture Hatcheries Across Khyber Pakhtunkhwa, Pakistan

Effects of stocking density and water flow rate on performance, water quality and economic benefits of African catfish larvae (Clarias gariepinus Burchell, 1822) in the aquaponic system integrated with Azolla fern

The effect of stocking on fish performance is known is most systems, and for many fish. Meanwhile water flow rate remains an important factor in recirculating aquaculture systems. However less information is still available on the influence of aquaculture management practices on the performance of aquaponics. This study determined the effect of stocking density and water flow rate on growth performance of African catfish larvae (Clarias gariepinus) and Azolla spp. in catfish-Azolla aquaponics system. The 4 × 4 factorial experiment consisted of four larval stocking densities (1500 larvae/m3, 3000 larvae/m3, 4500 larvae/m3 and 6000 larvae/m3) and four water flow rates (0.25 L/min, 0.5 L/min, 0.75 L/min and 1 L/min) executed in triplicate. The stocking density and water flow rate had an interactive influence (P < 0.05) on the concentration of DO, TAN, and NO3−. The stocking density and water flow rate had an interactive influence (P < 0.05) on the final mean weight, SGR, and survival of C. gariepinus larvae, but not for FCR and yield (P > 0.05). The highest fish weight was achieved under combination of stocking density 3245 larvae/m3 and water flow rate of 0.87 L/min, but growth will still be optimized upto a stocking density of 4850 larvae/m3 but at higher combinations of water flow rates (> 0.875 L/min). The stocking density and water flow rate had an interactive influence (P < 0.05) on chlorophyll a concentration, but not fresh weight, dry weight and yield (P > 0.05). Enterprise budgets for aquaponic with different stocking densities and water flow rate for fish and Azolla production allowed all the treatments to post positive returns to risk and were viable investments. Cash flow projections were made over a 10 year period for each of the units with the net present value (NPV) and internal rate of return (IRR) revealed that sales of larval fish and Azolla sp. at stocking density of 1500 larvae/m3 were not profitable. However, all the other stocking densities were profitable except at 3000 larvae/m3 and water flow rate of 0.25 L/min. Although at all stocking density the revenue were able to cover the variable costs, this study recommends stocking at 3000 to 4500 larvae/m3 and water flow rate of 0.75 L/min and 1.00 L/min.

Mapping of Sediment and Water Resources of Nadia District, West Bengal, India for Freshwater Aquaculture Management Practices

Present study relates to the fish growth, optimization and profitable fish production through pond sediment and water resources maps on sustainable basis. ALl blocks of Nadia district of West Bengal comprising of hot moist sub-humid agro-ecological region were thoroughly surveyed and physico-chemical characteristics of pond water and sediments were analysed. Based on the sediment and pond water resources an improved the fertilizer and manure management schedule, as well as maps have been prepared and demonstration of carp polyculture were carried out. All the fish species attained higher growth in the ponds of hot moist sub-humid agro-ecological regions (alluvial soils) following new nutrient management map over control. The average total fish production in experimental and control ponds was 5.184 and 3.095 tonnes/ha/yr, respectively.

A Study on The Level of Farmer Knowledge, Attitude and Practices on The Litopenaeus Vannamei Disease in Pond Culture

Litopenaeus Vannamei is a high-value commodity shrimp species in the aquaculture sector, especially Asia. Unfortunately, disease attack is a problem that emerges from shrimp aquaculture to gain high profit. Among the common disease that usually infects L. Vannamei are white spot disease (WSD) and Fusarium bacteria which causes black gill disease. This problem arises from farmers' lack of knowledge about shrimp disease, low management attitude and poor aquaculture management practices. Therefore, this research objective is to investigate a farmer's level of knowledge, attitude, and practices on the Litopenaeus Vannamei shrimp disease. The research method used in this study is a quantitative method (questionnaire survey) using a google form and the questionnaire was distributed online. The respondents were chosen from the L. Vannamei farmers (50 respondents) in Kota Bharu, Kelantan. The survey was open for one month between 15th November and 15th December 2021. The data was analysed using IBM SPPS software version 24.0 to obtain the frequency, percentage and descriptive analysis to analyse the level of knowledge, attitude and practices of L. Vannamei farmers on the shrimp disease in pond culture. This study showed that the level of knowledge, attitude, and practices of L. Vannamei farmers on the shrimp disease in pond culture is high, as can be seen by the good attitude in L. Vannamei management and having good aquaculture management practices. In conclusion, the high level of knowledge, attitude and practices of L. Vannamei farmers helps to motivate farmers to apply good management on shrimp cultivation to prevent the disease and increase the production of high-quality seeds.

Inland saline aquaculture increased carbon accumulation rate and stability in pond sediments under semi-arid climate

Similar to fresh- and brackish water aquaculture ponds, commercial shrimp farming in degraded saline areas holds the potential to bury carbon (C) in the sediments. However, studies on the mechanisms of sediment C dynamics and C-flux in response to inland saline aquaculture management practices are still scarce. Therefore, the objectives of the present study are to quantify the C burial rate in inland saline aquaculture ponds and assess the impact of inland saline aquaculture on sensitive C fractions in the bottom sediment of the ponds. The sediment samples (n = 12 from each pond) were collected from six shrimp farming ponds (1000 m2 area of each pond) of different ages. The sediment depth, sediment accumulation rate and the levels of total carbon (TC), total organic carbon (TOC) and sediment oxidizable organic carbon (SOC) and its different fractions were determined using standard procedures. The data were analysed by one-way analysis of variance (ANOVA), followed by the Duncan's multiple range test for comparing the means, and the Pearson correlation test was used to assess the relationship between the different pond sediment parameters and SOC content. The results revealed that the annual C accumulation rates varied from 902 to 1346 kg C ha−1 year−1 in 7-year-old earthen ponds (EPs) and bottom cemented ponds (BCPs), respectively. The sediment C fractions, including TC, TOC, SOC and its fractions (very labile, VLc; labile, Lc; less labile, LLc), and non-labile carbon (NLc)) were progressively increased over the pond age. The inland saline aquaculture practices over the years increased both active (AC) and passive carbon (PC) pools in the pond sediments, helped in the restoration and improvement of sediment quality and enhanced C sequestration potential of the sediments. Furthermore, a significant increase in the level of particulate organic carbon (POC) in BCPs justified that the non-ploughing practices at BCPs facilitated the formation of macro- and micro-aggregates, thereby increasing the C retention and stability of the pond sediments. This study suggested that the shrimp farming ponds in semi-arid saline soils represented considerable C burial hotspots, enhanced the stable passive C pools and improved the sediment quality.

Indonesian Government Mitigation Efforts towards Climate Change in the Marine and Fisheries Sector

Aims: This study aims to determine the Indonesian Government's mitigation efforts in dealing with climate change, especially in the marine and fisheries sector.&#x0D; Study Design: Literature study model.&#x0D; Place and Duration of Study: Yogyakarta, Indonesia; 2020-2021.&#x0D; Methodology: This study method utilized a qualitative approach with a literature study model. Sixty scientific national and international journals, online mass media, and legislations were collected. Data sources were used to explain the mitigation policy analysis of climate change in the marine and fisheries sector. The study stages started from article searching, theme classification, literature mapping based on discussions of various scientific journals, books, and online mass media with different orientations, data analysis, interpretation, and data presentation.&#x0D; Results: The results of the study reveal that the impact of climate change on the marine and fisheries sector is very significant so that the Indonesian government establishes various policies, undertakes mitigation efforts to strengthen its identity as a maritime country, eradicates illegal, unreported, unregulated (IUU) fishing, imposes a moratorium on ex-foreign ships, accelerates the growth of national economy, enhance food sovereignty and promote the development of maritime and marine economies. However, there are still problems in implementing policies, so it is necessary to improve the management system for climate change countermeasures in the marine and fisheries sector in Indonesia.&#x0D; Conclusion: Mitigation strategies in the marine and fisheries sector in Indonesia that can be implemented include applying sustainable aquaculture management practices suitable for carrying capacity and developing an integrated cultivation system. Various climate change mitigation policies in the marine and fisheries sector of the Government of Indonesia are commendable given many recognized successes, but there are still many problems with policy implementation. Ineffective application of policies is due to the government's focus on tackling climate change based on forestry and energy sectors, weak application of laws, and other problems. There is still a need for improvement in the management system for climate change countermeasures in Indonesia's marine and fisheries sector.

Assessment of Fish Farmers Use of Recommended Management Practices in Oyo State, Nigeria

The enhancement of fish production through aquaculture can be brought about by enhancing farmers’ utilization of information on new innovations and recommended practices. This study was carried out to assess fish farmers’ use of recommended management practices in Oyo state. One hundred and fifty fish farmers were selected from the four agricultural zones in the state using multistage sampling technique. Primary Data were analyzed using descriptive and multiple regression analysis. Most of the fish farmers were male (88%), 78% had tertiary education and 68% had &lt;11years of experience in fish farming. The study revealed that the rate of adoption of recommended aquaculture management practices was 46.7%. The regression analysis also revealed a linear relationship between the socio-economic characteristic and adoption of RAMP (R2 = 0879). Educational background (p&lt;0.05), years of experience (p&lt;0.1) and method of farming (p&lt;0.05) were positively significant. The use of these management practices were also limited by different factors as revealed in the study. In conclusion, the adoption of recommended management by fish farmers is not encouraging enough. Strong cooperation between the fish farmers and extension agents was highly recommended.

Farmers' use of Improved Aquaculture Managment Practices in Western Zone of Lagos State Agricultural Development Programme (ADP), Nigeria

Improved Aquaculture Management Practices (LAMP) always lead to increase productivity, generate greater income, reduce poverty and improve livelihood. This study assessed the extent of the use of IAMP by fish farmers in the Western Zone of Lagos state ADP, Nigeria to describe level of usage of IAMP and examine the constraints faced by fish farmers in the use of IAMP The primary data were collected with the aid of structured interview guide, administered through personal interviews and observations to elicit information from 100 fish farmers using simple random sampling and purposive technique. Descriptive statistics was used to analysis the socio-economic characteristics, while budgetary analysis was used to determine the profitability and multiple regression analysis. Findings show that the mean age of the respondents was 42.6 years, 71.0% were male, 90.0% married, 63.0% secondary occupation and 84.81% were aware of IAMP On a daily basis, 87.0% of the respondents were involved in record keeping, 82.0% carried out general observation in the farm and used concrete tanks while site selection, tank construction, pond liming and use of drugs were done occasionally. Constraints faced by the respondents were high cost of inputs (88.0%), flooding (79.0%),. predators (71.0%), mortality (61.0%), pollution (61.0%), inadequate technical know-how (61.0%) and disease outbreak (58.0%). Respondents' household size (r = -0.202, p&lt;0.05) and marital status (χ2= 61.082, P&lt;005) were significantly associated with factors affecting the use of IAMP. There were significant differences between IAMP used and revenue generated (t =4.641.,p&lt;0.05). In conclusion, adoption of IAMP leads to increase aquaculture productivity and changes of social status. Government should provide assistance in loan at low interest, appropriate land, grants, fish farm input at subsidized rate adequate marketing information and networking among fish farmers.

Aquaculture management practices associated with antimicrobial residues in Southwestern Nigeria

Aquaculture production has grown rapidly in Nigeria but with unbridled use of antibiotics which predisposes fish consumers to the risks of antimicrobial residues and resistance. A cross sectional survey of antimicrobial use in aquaculture and occurrence of their residues in African Catfish (Clarias gariepinus) samples from Southwestern states of Nigeria were carried out. The results showed that majority of the farmers lacked knowledge of drug residues in aquatic animals, and the food safety and public health implications on consumers. Frequently administered antibiotics include tetracyclines (27.5%), chloramphenicol (22.0%) and gentamicin (18.4%). About 84.7% of tested fish had residues with variable prevalence which were not statistically significant. Risk factor analysis indicated that fish farmers with tertiary and secondary education were more likely to produce fish that contained antimicrobial residues than those with primary education [odds ratio (OR) = 1.91, confidence interval (CI) = 1.24–5.99 and OR = 1.25, CI = 1.08–5.27, respectively] while fish from farms managed by men were about three times more likely to contain residues (OR = 3.25, 95% CI = 1.95–9.35) than those managed by women. Hence, most of the fish from Southwestern Nigeria were indiscriminately dosed with different antibiotics that predispose consumers to the risks of antimicrobial residues with food safety and antimicrobial resistance consequences. Implementation of good fishery management practices and farmers' education are advocated to reduce dependence on antimicrobials.

Characterization of a Y-specific duplication/insertion of the anti-Mullerian hormone type II receptor gene based on a chromosome-scale genome assembly of yellow perch, Perca flavescens.

Yellow perch, Perca flavescens, is an ecologically and economically important species native to a large portion of the northern United States and southern Canada and is also a promising candidate species for aquaculture. However, no yellow perch reference genome has been available to facilitate improvements in both fisheries and aquaculture management practices. By combining Oxford Nanopore Technologies long-reads, 10X Genomics Illumina short linked reads and a chromosome contact map produced with Hi-C, we generated a high-continuity chromosome-scale yellow perch genome assembly of 877.4 Mb. It contains, in agreement with the known diploid chromosome yellow perch count, 24 chromosome-size scaffolds covering 98.8% of the complete assembly (N50=37.4Mb, L50=11). We also provide a first characterization of the yellow perch sex determination locus that contains a male-specific duplicate of the anti-Mullerian hormone type II receptor gene (amhr2by) inserted at the proximal end of the Y chromosome (chromosome 9). Using this sex-specific information, we developed a simple PCR genotyping assay which accurately differentiates XY genetic males (amhr2by+ ) from XX genetic females (amhr2by- ). Our high-quality genome assembly is an important genomic resource for future studies on yellow perch ecology, toxicology, fisheries and aquaculture research. In addition, characterization of the amhr2by gene as a candidate sex-determining gene in yellow perch provides a new example of the recurrent implication of the transforming growth factor beta pathway in fish sex determination, and highlights gene duplication as an important genomic mechanism for the emergence of new master sex determination genes.

Management practices in the beel aquaculture system at Rajshahi, northwest Bangladesh

Open aquatic system such as beel is an important freshwater resource for agriculture and aquaculture.This study was conducted (July-December 2014) to describe the beel aquaculture management practices in the Hagla Beel at Bagmara upazila under Rajshahi district.The Beel fish farming area was 20.25 ha and irregular in shape with average depth 1.5 m. During the study period, the measured water quality parameters of the beel were within the suitable range for aquaculture. Eight genera of phytoplankton and eight genera of zooplankton were identified from the beel water body. Four native and 4 exotic fish species with sizes ranging from 0.15-1.11 kg were stocked for growing in the beel. At the end of culture period, the production of fish was 2,622.15 kg/ha and cost-benefit ratio (CBR) was 1:1.42. Environmental problems such as increasing of water temperature and decreasing of water level during summer, and parasitic diseases were some of the risks in beel fish farming system. The results of this study should be useful for beel aquaculture, and for the farmers and resource manager for harnessing maximum benefits from the beel resources in Bangladesh.&#x0D; J. bio-sci. 28: 43-50, 2020

The role of sedimentation in the structuring of microbial communities in biofloc-dominated aquaculture tanks

In no water exchange aquaculture operations, sedimentation has been employed to control the level of microbial flocs to decrease oxygen consumption and to prevent clogging of gills in cultured organisms. Nevertheless, the impact of this practice on the culture microbial community was not documented. The current study evaluated the impact of adding different concentrations of sedimentation from an intensive shrimp culture tank on the microbial communities in an experimental tank system operated with no water exchange. The trial evaluated three concentrations (mg L−1) of total suspended solids levels: <200, 680, and 1030. The analysis showed that settleable microbial community has a different set of species compared with the unsettled biomass, which was also less diverse. We argue that the difference in species composition is probably related to the biological flocculation, i.e., the ability exhibited by microorganisms to spontaneously form large, dense and quick settling aggregates. The results suggest that settling tanks act as a selective force by reducing the abundance of microorganisms strongly associated with the settled flocs, whilst favoring planktonic lifestyle bacteria or microorganisms associated with small and open flocs. These effects, especially loss of diversity, need to be considered in aquaculture management practices since it can increase the risk for invasion of opportunistic pathogenic species.

Identification of Vibrio species isolated from cultured olive flounder (Paralichthys olivaceus) in Jeju Island, South Korea

Olive flounder (Paralichthys olivaceus) is the major species developed for aquaculture in South Korea. Over the long history of olive flounder aquaculture, complex and diverse diseases have been a major problem, negatively impacting industrial production. Vibriosis is a prolific disease which continuously damages olive flounder aquaculture. A bacterial disease survey was performed from January to June 2017 on 20 olive flounder farms on Jeju Island. A total of 1710 fish were sampled, and bacteria from the external and internal organs of 560 fish were collected. Bacterial strains were identified using 16 s rRNA sequencing. Twenty-seven species and 184 strains of Vibrio were isolated during this survey, and phylogenetic analysis was performed. Bacterial isolates were investigated for the distribution of pathogenic and non-pathogenic species, as well as bacterial presence in tested organs was characterized. V. gigantis and V. scophthalmi were the dominant non-pathogenic and pathogenic strains isolated during this survey, respectively. This study provides data on specific Vibrio spp. isolated from cultured olive flounder in an effort to provide direction for future research and inform aquaculture management practices.

Economics of Sustainable Intensification of Aquaculture: Evidence from Shrimp Farms in Vietnam and Thailand

AbstractThere is growing interest in sustainable intensification of aquaculture production. Yet little economic analysis has been done on farm‐level effects of the economic sustainability of production intensification. Data from 83 shrimp farms (43 in Vietnam and 40 in Thailand) were used to identify (through principal component and cluster analyses) 13 clusters of management practices that reflected various scales of production intensity that ranged from 0–1999 kg/ha/crop to 10,000 kg/ha/crop and above, for both Penaeus monodon and Litopenaeus vannamei in Vietnam and Thailand. The clusters identified reflected sets of management practices that resulted in differing yields despite similarities in stocking densities among some clusters. The enterprise budget analysis developed showed that the more intensively managed clusters outperformed the less intensively managed clusters in economic terms. More intensively managed farm clusters had lower costs per metric ton of shrimp produced and were more profitable. The greater yields of shrimp produced per hectare of land and water resources in more intensively managed shrimp farms spread annual fixed costs across a greater volume of shrimp produced and reduced the cost per metric ton of shrimp. Costs per metric ton of shrimp produced decreased from the lowest to the highest intensity level (from US$10,245 at lowest intensity to US$3484 at highest for P. monodon and from US$24,301 to US$5387 for L. vannamei in Vietnam and from US$8184 at the lowest intensity level to US$3817 at the highest intensity level per metric ton for L. vannamei in Thailand). Costs of pond amendments used in shrimp production were particularly high in Vietnam and largely unwarranted, whereas fixed costs associated with the value of land, production facilities, equipment, and labor were sufficiently high in Thailand so that net returns were negative in the long run. Nevertheless, economic losses in Thailand were less at greater levels of intensification. The study demonstrated a clear value proposition for shrimp farmers to use natural resources (such as land) and other inputs in an efficient manner and supports findings from corresponding research on farm‐level natural resource use efficiency. Additional research that incorporates economic analysis into on‐farm studies of sustainable intensification of aquaculture is needed to provide ongoing guidance related to sustainable management practices for aquaculture.

Metal content of kelp (Laminaria digitata) co-cultivated with Atlantic salmon in an Integrated Multi-Trophic Aquaculture system

Aquaculture is the most rapidly expanding food production sector and this trend is projected to continue in the coming decades. Intensification of farming methods alongside a tendency for farming higher trophic level species has led to concerns over nutrient loading of coastal waters. Where this is the case, Integrated Multi-Trophic Aquaculture (IMTA) has been proposed as a best-practice management option for reducing environmental impact. Fed aquaculture can also affect metal concentrations of surrounding biota by acting as a point source of contamination or by altering the abiotic environment in a manner that affects the capacity of organisms to accumulate metals. Seaweeds are integral to IMTA in providing the inorganic nutrient extraction component of the system, however it is unknown whether their close proximity to other aquaculture operations facilitates increased metal accumulation. As a result, the effect of cultivation and growth environment on accumulation of metals in the kelp Laminaria digitata (Hudson) J.V. Lamouroux was investigated, providing the first comparative experimental data examining the effect of multi-species cultivation on trace metal content of macroalgae. Thalli of L. digitata growing wild, cultivated as a single species (mono-cultivated), and cultivated alongside organic Irish salmon aquaculture facilities (IMTA) were analysed for metal content (As, Ba, Cd, Co, Cu, Mn, Sb, V, Zn). Cultivation in an IMTA context raised the content of Cu, Mn and V relative to that in mono-cultivated seaweeds however concentrations of metals were within the range of those from algae collected from undisturbed wild populations. Metal levels in the seaweeds do not pose a concern over inclusion as a dietary component with the possible exception of arsenic that exceeded some legislative limits. The results of this study provide novel information that can inform policy and sustainable aquaculture management practices aimed at reducing contamination of the aquatic environment and the impact on consumers. Statement of relevanceThis study provides the first comparative investigation of metals in seaweed from different cultivation environments and can be used to support best-practice management decisions involving IMTA. Laminaria digitata metal content was marginally increased for copper, manganese and vanadium at IMTA sites. Vanadium and antimony (emerging contaminants) in the commercially important seaweed L. digitata are reported for the first time.

Integrating spatial land use analysis and mathematical material flow analysis for nutrient management: a case study of the Bang Pakong River Basin in Thailand.

Rivers in developing and emerging countries often lack good water quality. Tools to assess the water quality in rivers, including identification of possible sources of pollution, are therefore of increasing importance. The aim of this study is to apply mathematical material flow and spatial land use analyses to identify and geographically locate the main nitrogen and phosphorus sources and processes in Bang Pakong Basin (BPB). Potential measures to mitigate the nitrogen and phosphorus loads to the water system can then be efficiently evaluated. The combination of these two methods reveals the overall nutrient load as well as local "hot spots." This allows possible mitigation measures to be discussed with regard to their spatial location. This approach goes beyond previous work in which mathematical material flow analysis was shown to be a useful tool to investigate sources of nutrients regardless of their location. The results show that the main sources contributing nutrients to waterways are aquaculture, such as shrimp, tilapia, catfish, and sea bass farming, as well as rice paddies along the main river. Additional sources contributing nutrients to this basin are field crops, livestock, aquaculture, households, and industry. High levels of nutrient inflows come from feeds and fertilizers through aquaculture and rice cultivation. The excess nutrients run into the waterways by direct discharge from aquaculture and runoff processes from rice paddies. Scenario analysis shows that management practices for aquaculture, rice, pig, and poultry farming are key drivers for reducing nutrients in the BPB.

Adoption of Improved Aquaculture Management Practices by Cluster Fish Farmers in Delta State, Nigeria

The adoption of proven fish production management practices portends many economics and social implications. Interview schedule was employed to generate primary data from 146 respondents in the four cluster fish farms (estates) in two local government areas and analyzed with descriptive and inferential statistics. Information on socio economic characteristics revealed that most of the respondents were in the active age bracket of 30-40 years, well educated and small scale fish farmers with fewer years of experience members at fish farmers association and married. Fellow farmers (57.5%) were major source of information on fish farming since the farmers were brought together under the umbrella body of fish farmers’ association. The study further revealed a low adoption level for all the management practices on adoption index of 0.43 which means that the farmers had only 43% adoption of the practices. Age, education and fish farming experience of fish farmers correlate with the adoption of some improved aquaculture management practices. In view of prevailing evidence regular training and workshops to update the knowledge and information on modern aquaculture practices should be organized for fish farmers.

Jackknife-corrected parametric bootstrap estimates of growth rates in bivalve mollusks using nearest living relatives

Quantitative estimates of growth rates can augment ecological and paleontological applications of body-size data. However, in contrast to body-size estimates, assessing growth rates is often time-consuming, expensive, or unattainable. Here we use an indirect approach, a jackknife-corrected parametric bootstrap, for efficient approximation of growth rates using nearest living relatives with known age–size relationships. The estimate is developed by (1) collecting a sample of published growth rates of closely related species, (2) calculating the average growth curve using those published age–size relationships, (3) resampling iteratively these empirically known growth curves to estimate the standard errors and confidence bands around the average growth curve, and (4) applying the resulting estimate of uncertainty to bracket age–size relationships of the species of interest. This approach was applied to three monophyletic families (Donacidae, Mactridae, and Semelidae) of mollusk bivalves, a group characterized by indeterministic shell growth, but widely used in ecological, paleontological, and geochemical research. The resulting indirect estimates were tested against two previously published geochemical studies and, in both cases, yielded highly congruent age estimates. In addition, a case study in applied fisheries was used to illustrate the potential of the proposed approach for augmenting aquaculture management practices. The resulting estimates of growth rates place body size data in a constrained temporal context and confidence intervals associated with resampling estimates allow for assessing the statistical uncertainty around derived temporal ranges. The indirect approach should allow for improved evaluation of diverse research questions, from sustainability of industrial shellfish harvesting to climatic interpretations of stable isotope proxies extracted from fossil skeletons.