Pond Density Research Articles

Mud crab, Scylla tranquebarica (Fabricius, 1798), crablet grow‐out in lined ponds with different stocking densities to support soft‐shell crab production

AbstractCrab stocking densities in brackish water ponds can influence crab growth rate, survival, and production volume. This study aimed to determine the optimum grow‐out stocking density for Scylla tranquebarica crablets reared in lined ponds to supply the soft‐shell crab industry. Three stocking density treatments (1, 4, and 8 ind./m2) were applied to crablets reared in lined ponds for 90 days. The crablets were fed low‐value fish (Leiognathus equula) at an initial rate of 100% of total body weight for two weeks, reduced to 3% toward the end of the study. Crablets stocked at 1 and 4 ind./m2 had a significantly (p < 0.05) higher net growth (NG) and daily growth rate (DGR) than crablets stocked at 8 ind./m2. Deformed crabs were also most common at the highest stocking density. The intermediate stocking rate achieved moderate survival and feed conversion rates, with the highest crab production volume (19.65 ± 0.10 kg/100 m2) and net income (6845.60 US$/Ha/2 crops/year). Based on these findings, a stocking rate of around 4 ind./m2 is recommended for the grow‐out of S. tranquebarica crablets in lined ponds.

Greenhouse gases emissions from aquaculture ponds: Different emission patterns and key microbial processes affected by increased nitrogen loading

Global aquaculture production is expected to rise to meet the growing demand for food worldwide, potentially leading to increased anthropogenic greenhouse gases (GHG) emissions. As the demand for fish protein increases, so will stocking density, feeding amounts, and nitrogen loading in aquaculture ponds. However, the impact of GHG emissions and the underlying microbial processes remain poorly understood. This study investigated the GHG emission characteristics, key microbial processes, and environmental drivers underlying GHG emissions in low and high nitrogen loading aquaculture ponds (LNP and HNP). The N2O flux in HNP (43.1 ± 11.3 μmol m−2 d−1) was significantly higher than in LNP (−11.3 ± 25.1 μmol m−2 d−1), while the dissolved N2O concentration in HNP (52.8 ± 7.1 nmol L−1) was 150 % higher than in LNP (p < 0.01). However, the methane (CH4) and carbon dioxide (CO2) fluxes and concentrations showed no significant differences (p > 0.05). N2O replaced CH4 as the main source of Global Warming Potential in HNP. Pond sediments acted as a sink for N2O but a source for CH4 and CO2. The △N2O/(△N2O + △N2) in HNP (0.015 ± 0.007 %) was 7.7-fold higher than in LNP (0.002 ± 0.001 %) (p < 0.05). The chemical oxygen demand to NO2-N ratio was the most important environmental factor explaining the variability of N2O fluxes. Ammonia-oxidizing bacteria driven nitrification in water was the predominant N2O source, while comammox-driven nitrification and nosZII-driven N2O reduction in water were key processes for reducing N2O emission in LNP but decreased in HNP. The strong CH4 oxidization by Methylocystis and CO2 assimilation by algae resulted in low CH4 emissions and CO2 sink in the aquaculture pond. The Mantel test indicated that HNP increased N2O fluxes mainly through altering functional genes composition in water and sediment. Our findings suggest that there is a significant underestimation of N2O emissions without considering the significantly increased △N2O/(△N2O + △N2) caused by increased nitrogen loading.

Prioritizing landscapes for mitigating the impacts of onshore wind farms on multidimensional waterbird diversity in the Yellow Sea

Abstract Ongoing wind energy developments play a key role in mitigating the global effects of climate change and the energy crisis; however, they have complex ecological consequences for many flying animals. The Yellow Sea coast is considered as an ecological bottleneck for migratory waterbirds along the East Asian–Australasian flyway (EAAF), and is also an important wind farm base in China. However, the effects of large-scale onshore wind farms along the EAAF on multidimensional waterbird diversity, and how to mitigate these effects, remain unclear. Here we examined how wind farms and their surrounding landscapes affected multidimensional waterbird diversity along the Yellow Sea coast. Taxonomic, functional, and phylogenetic diversity of the waterbird assemblages, and mean pairwise distances and nearest taxon distances with null models were quantified in relation to 4 different wind turbine densities. We also measured 6 landscape variables. Multi-dimensional waterbird diversity (taxonomic, functional, and phylogenetic diversity) significantly decreased with increasing wind turbine density. Functional and phylogenetic structures tended to be clustered in waterbird communities, and environmental filtering drove waterbird community assemblages. Furthermore, waterbird diversity was regulated by a combination of wind turbine density and landscape variables, with edge density of aquaculture ponds, in addition to wind turbine density, having the greatest independent contribution to waterbird diversity. These results suggest that attempts to mitigate the impact of wind farms on waterbird diversity could involve the landscape transformation of wind farm regions, for example, by including high-edge-density aquaculture ponds (i.e., industrial ponds) around wind farms, instead of traditional low-edge-density aquaculture ponds.

Landscape Drivers Influence the Efficiency of Management of Aquatic Invasive Alien Rodents in Western France

Managing invasive alien species (IAS) is a critical issue for many countries to preserve native biodiversity, ecosystem services and human well-being. In western France, we analyzed data of captures of aquatic invasive alien rodents (AIARs), the coypu and muskrat, by the local permanent control program from 2007 to 2022 across 26 municipalities encompassing 631 km2. We found that control activities removed up to 10.3 AIARs per km2 annually. The number of coypus removed per trapper per year increased by 220%, whereas it decreased by 85% for muskrats. The number of trappers increased from 2007 to 2014, peaking at 70, and then decreased by 50% in 2022. The number of AIARs captured per trapper per year increased with the density of ponds. The number of coypus captured per year decreased with an increasing amount of woodland per municipality, whereas it increased with road density. Finally, other tested landscape variables did not affect the number of AIARs removed per trapper per year. Our results are discussed in the context of control activities implemented against IAS in other countries. We advocate for stakeholders to assess whether control activities against AIARs effectively mitigate the impacts on social-ecological systems in France.

The Relationship Between Water Quality and Phytoplankton Abundance with Different Showing Density in Litopenaeus vannamei Ponds in Bayeman Village, Probolinggo District, East Java

Intensive ponds often experience a decrease in water quality and cause ponds to bloom due to the fertility of the pond bottom due to the buildup of organic material originating from leftover feed, feces and the remains of dead shrimp. The aim of this research is to determine the relationship between water quality and phytoplankton abundance in intensive pond types with different densities in Bayeman Village, Probolinggo Regency. The research was carried out from January to March 2023. Samples were taken using the purposive sampling method in 6 different pond plots. Phytoplankton analysis was carried out at the Laboratory of the Sand Source Freshwater Fisheries Technical Implementation Unit and the Hydrobiology Laboratory of the Fish Resources Section of the Faculty of Fisheries and Marine Sciences. Measurement of in situ water quality parameters, namely temperature, pH, brightness, DO, TDS, light intensity, salinity and ex situ nitrate, phosphate and ammonia using spectrophotometric methods. The correlation test results of physico-chemical parameters related to phytoplankton abundance have a strong and heterogeneous relationship only with the orthophosphate parameter

Growth rate and survival of green shells (perna viridis l.) In ponds, alue naga village, banda aceh

Alue Naga is one of the coastal and marine areas in the city of Banda Aceh which has the potential for aquaculture and high economic value, namely green mussels (Perna viridis L). This research aims to determine the growth and survival rate of green mussels with different stocking densities in Alue Naga ponds which are still influenced by the tides of seawater. The layout of the green mussel cultivation container is at the pond water gate. The method used is an experimental test method using a Completely Randomized Design (CRD) model with 3 treatments, each treatment 3 times repeated. Research shows that the best average growth and survival rate for green mussels are found in treatment A with a stocking density of 20 seeds/basket, absolute length growth with an average value of 45.52 ± 0.42 mm, weekly length growth rate with an average value -an average of 3.79 ± 0.03 mm/week and an average weight of 25.92 ± 0.19 grams, while the survival rate reached 91.66%. Differences in green mussel stocking density had a significant effect on absolute length growth (PM), absolute weight (BM), and weekly length growth rate (LPPM), while survival (SR) had no significant effect.

Technological parameters of carp growing (Cyprinus carpio) at different stocking densities

This article presents a study of the technology of growing carp (Cyprinus carpio) using different stocking densities in feeding ponds. Carp is one of the most common and essential freshwater fish species for commercial farming and consumption. The study was conducted over several months, with an assessment of carp's growth, survival, and productivity when using different stocking densities in feeding ponds. Different stocking densities included low (sparse), medium, and high (dense) carp individuals per unit area. To experiment, four groups of carp individuals were kept in feeding ponds at different stocking densities from 2,000 to 3,500 specimens per hectare of water area. Using extensive planting material of carp with an average weight of 55 g makes it possible to obtain commercial carp with an average weight of 485 g to 650 g during a two-year cycle of cultivation in the conditions of the second fish farming zone without reducing fish production. At the same time, the largest concentration of carp was obtained in a pond with sparse planting of annuals – 2.0 thousand specimens/ha. An increase in the planting density of yearlings of carp to 3.5 thousand units/ha led to a decrease in the average daily weight of two-year-old carp to 510 g while maintaining a high fish production of 1122 kg/ha. At the same time, a hydrochemical analysis was carried out in the ponds, and the amount and biomass of the natural feed base (phyto-, zooplankton, and zoobenthos) were determined. The analysis of the research results indicates that the stocking density of carp has a significant impact on its productivity. The sparse stocking conditions promoted more significant growth and better development of the fish, which may be due to less competition for food and space. On the other hand, high stocking density led to a slight decrease in growth and did not affect survival and fish productivity. The results of this study have practical applications for fish farms engaged in the cultivation of carp. They emphasize the importance of an optimal balance between the number of fish, the availability of natural feed, and the area of the feeding ponds in order to achieve maximum growth and productivity with minimum costs of keeping and feeding the fish. Such research will help improve fish farming technologies and optimize production processes to ensure sustainable and efficient development of the industry.

Production Performances and Profitability of Stocking Homestead Ponds with Advanced Carp Fingerlings for Maximizing Family Nutrition and Income Generation

Coastal homestead ponds are flooded during the rainy season and only hold water for five to six months. For coastal rural people, these ponds have a substantial impact on household nutrition and income generation. However, choosing the right culture techniques, stocking density, and seed size are necessary for fish aquaculture to be effective in this sort of seasonal pond. Hence, an adaptive field experiment was conducted to reveal the growth performance, yield and cost–benefit using advanced carp fingerling at different stocking densities in homestead ponds. Advanced fingerlings of Gibelion catla, Labeo rohita, Cirrhinus cirrhosus, and Labeo calbasu with the mean individual stocking weight of 243 ± 1.87 g, 223.56 ± 2.35 g, 155.89 ± 1.69 g, and 158.72 ± 1.35 g, respectively, were stocked at three different stocking densities, e.g., 825 kg ha−1 in T1, 560 kg ha−1 in T2 and 370 kg ha−1 in T3 and reared for 5 months. Homemade supplementary feed with protein content of 24.25% was supplied twice daily. The specific growth rate (SGR) was recorded highest at T3 for all the cultured species as L. rohita (1.15 ± 0.01% day−1), followed by G. catla (1.12 ± 0.004% day−1), L. calbasu (1.09 ± 0.01% day−1), and C. cirrhosus (0.98 ± 0.002% day−1), respectively. An inverse relationship was detected between fish growth and stocking density for all treatments. A similar pattern was observed in the survival rate, where reduced survival rates were recorded at T1 for all species. Significant variation (p &lt; 0.05) was found among the treatments in terms of final weight, SGR, and survival rate. Economics of the carp polyculture also showed the highest net benefit (2609.77 ± 2.02 USD ha−1) and benefit–cost ratio (2.06 ± 0.002) at T3. Rearing of fish at 370 kg ha−1 stocking density yielded 129.21% and 110.96% higher production in T3 than T1 and T2, respectively. Overall, T3 treatment was more appropriate than T1 and T2 due to its low FCR, low investment but high survival rate, and net return. Therefore, stocking homestead ponds with advanced carp fingerling with a density of 370 kg per ha can be suggested as for increasing fish production and benefit in the homestead ponds of coastal rural area. In addition, further research is recommended to find out the effects of feeding and sources of seeds on the production performances.

An evidence-based study mapping the decline in freshwater ponds in the Severn Vale catchment in the UK between 1900 and 2019

Freshwater ponds have long been an overlooked biodiversity store and changing types of land use and the land management practices has led to a steady decline in pond numbers. Establishing the regional extent of pond loss is the first step in identifying key areas for conservation action. This study calculated pond loss in the Severn Vale catchment UK since 1900. Identification of pond location and surrounding land use on historic and contemporary maps enabled a comparison of total number, density and distance between present day and historic ponds. 57.7% of ponds present in 1900 were lost and pond density declined from 7.3 to 4.5 ponds km−2 between 1900 and 2019. This resulted in a 24.6 m increase in the average distance between contemporary ponds. Land use was an important factor in determining pond loss. Although in 2019 the highest density of ponds are in rural areas, 62.3% of ponds lost were from agricultural settings (arable or pasture). Our results highlight the significant pond loss experienced in the Severn Vale since 1900 and provide a valuable baseline for pondscape restoration. The methods described are widely applicable to other regions either with a history of ponds or an environment that could sustain them.

Water parameters correlated with the zootechnical performance of shrimp Litopenaeus vannamei grown in oligohaline waters

The present study aimed to correlate the influence of water quality, cultivation time, area, and density of ponds on the zootechnical performance of shrimp Litopenaeus vannamei in oligohaline waters. It was demonstrated that, under the conditions of this research, better control of temperature, pH and water alkalinity can be employed. Ammonia levels were within the normal range and correlated positively with the growth rate (ρ = 0.69859) and production (ρ = 0.66362) of the ponds. There was also a positive correlation between cultivation time and pond density with shrimp weight (ρ = 0.75305 and 0.68933) and pond productivity (ρ = 0.74763 and 0.79367, respectively). Negative correlations were observed between: I) pH with shrimp survival (ρ = -0.73238) and pond production (ρ = -0.68696); II) alkalinity and pond production (ρ = -0.66162). The results show that the cultivation of shrimp L. vannamei in oligohaline waters is viable and there is potential for increased productivity associated with better hydrological monitoring and use of higher density and cultivation time by some producers.

Growth and production of pacific white shrimp Litopenaeus vannamei (Boone, 1931) with different stocking densities in semi-intensive brackishwater liner ponds, Chennai, India: Technical report

Pacific white shrimp (Penaeus vannamei) is one of the main fishery products in fisheries sector. It has suitable for farming, stable production, easy to stocking high density, and highly diseases resistance. Most of the farmers in India choose to cultivate vannamei shrimp. Moreover, there are still other advantages of vannamei shrimp, its euryhaline species. No proper research yet been recorded on the effect of stocking density in survival rate and growth performance of L. vannamei. The aim of this report was to evaluate the growth, survival, and production performance of white shrimp (P. vannamei) in brackishwater liner ponds at different stocking densities.

The Assessment of Water Compatibility of Adaptable Stick-Net Cage for Resilience Milkfish Cultivation in Tanjung Mas, Indonesia

Milkfish cultivation becomes the main livelihood of farmers in coastal areas. However, the land for milkfish cultivation is shrinking due to land use for settlements, industries, and sea-level rise. A Stick-net cage is an aquaculture solution in limited space for an inland fishpond. It can be placed in seashore areas while maintaining the quality of the aquatic environment and nutrient circulation. This study aims to analyze water compatibility in the stick-net cage areas for supporting sustainable aquaculture activities. An exploratory observational study was conducted in Tanjung Mas Village, Semarang, Central Java, Indonesia. Ten sampling areas were determined purposively by considering the point locations toward household wastewater and industrial outfalls. Based on these criteria, the ten stations used as sample areas were divided into industrial outfall areas (1st – 5th station) and areas close to the open sea (6th – 10th station). Physical parameters in the sampling areas, including temperature, water-current, turbidity, and clearness, met seawater standards for milkfish cultivation. Chemical indicators, such as NH4 and P in water, were very high, which may be caused by domestic and industrial waste contamination and increased organic fermentation activity on the seabed. However, the existing stick-net cages have exceeded the capacity of the coastal water areas. In general, the physicochemical parameters in the Tanjung Mas water area are suitable for milkfish cultivation. However, it is necessary to reduce the amount of pond density to give growth space for milkfish. In addition, wastewater management and treatment plants should be built up to reduce water contamination.

Agricultural intensification alters marbled newt genetic diversity and gene flow through density and dispersal reduction.

Recent agricultural intensification threatens global biodiversity with amphibians being one of the most impacted groups. Because of their biphasic life cycle, amphibians are particularly vulnerable to habitat loss and fragmentation that often result in small, isolated populations and loss of genetic diversity. Here, we studied how landscape heterogeneity affects genetic diversity, gene flow and demographic parameters in the marbled newt, Triturus marmoratus, over a hedgerow network landscape in Western France. While the northern part of the study area consists of preserved hedged farmland, the southern part was more profoundly converted for intensive arable crops production after WWII. Based on 67sampled ponds and 10microsatellite loci, we characterized regional population genetic structure and evaluated the correlation between landscape variables and (i) local genetic diversity using mixed models and (ii) genetic distance using multiple regression methods and commonality analysis. We identified a single genetic population characterized by a spatially heterogeneous isolation-by-distance pattern. Pond density in the surrounding landscape positively affected local genetic diversity while arable crop land cover negatively affected gene flow and connectivity. We used demographic inferences to quantitatively assess differences in effective population density and dispersal between the contrasted landscapes characterizing the northern and southern parts of the study area. Altogether, results suggest recent land conversion affected T. marmoratus through reduction in both effective population density and dispersal due to habitat loss and reduced connectivity.

A Three-Phase Approach to Production of Shedding Crabs (Callinectes sapidus) in Low Salinity Ponds in Mississippi

The ability to reliably produce small blue crabs through aquaculture allows for expanded development of the soft crab industry in the United States with little or no impact to the wild fishery. Research on soft crab aquaculture in Mississippi is based on a three-phase approach: hatchery production of megalopae, salinity acclimation and grow-out of early juveniles in raceways, and final growth to shedding crabs in shallow ponds. Limited access to quality salt water or to hard water aquifers in Mississippi, coupled with the high cost associated with salting ponds led to the development of techniques to produce peeler crabs in reduced salinities. Hatchery success has been variable (average 14%) with significantly lower production following the Deepwater Horizon Oil disaster in 2011. Protocols for hatching and rearing of larvae and methods developed for intermediate grow-out and salinity acclimation of juveniles are reviewed as well as the adaptation of a folk-fishing technique to harvest peelers from the ponds. Economic studies defined production parameters necessary to reduce costs and attain profitability in low salinity (1) pond culture. Increased survivorship of larvae and juveniles during the hatchery, intermediate grow-out and pond phases and stocking density in ponds were key determinants of profitability. Simulation results at various stocking densities indicated that production of shedding crabs could be economically feasible. Although individual culture runs in the current research approached survival rates that would ensure profitability, routine survivorship is currently below the projected estimates necessary to achieve that goal.

Monthly biological larviciding associated with a tenfold decrease in larval density in fish farming ponds and reduced community-wide malaria incidence in northwestern Brazil

BackgroundLarvicides are typically applied to fixed and findable mosquito breeding sites, such as fish farming ponds used in commercial aquaculture, to kill immature forms and thereby reduce the size of adult malaria vector populations. However, there is little evidence suggesting that larviciding may suppress community-wide malaria transmission outside Africa. Here, we tested whether the biological larvicide VectoMax FG applied at monthly intervals to fish farming ponds can reduce malaria incidence in Amazonian Brazil.MethodsThis study was carried out in Vila Assis Brasil (VAB; population 1700), a peri-urban malaria hotspot in northwestern Brazil with a baseline annual parasite incidence of 553 malaria cases per 1000 inhabitants. The intervention consisted of monthly treatments with 20 kg/ha of VectoMax FG of all water-filled fish ponds in VAB (n ranging between 167 and 170) with a surface area between 20 and 8000 m2, using knapsack power mistblowers. We used single-group interrupted time-series analysis to compare monthly larval density measurements in fish ponds during a 14-month pre-intervention period (September 2017–October 2018), with measurements made during November 2018–October 2019 and shortly after the 12-month intervention (November 2019). We used interrupted time-series analysis with a comparison group to contrast the malaria incidence trends in VAB and nearby nonintervention localities before and during the intervention.ResultsAverage larval densities decreased tenfold in treated fish farming ponds, from 0.467 (95% confidence interval [CI], 0.444–0.490) anopheline larvae per dip pre-intervention (September 2017–October 2018) to 0.046 (95% CI, 0.041–0.051) larvae per dip during (November 2018–October 2019) and shortly after the intervention (November 2019). Average malaria incidence rates decreased by 0.08 (95% CI, 0.04–0.11) cases per 100 person-months (P < 0.0001) during the intervention in VAB and remained nearly unchanged in comparison localities. We estimate that the intervention averted 24.5 (95% CI, 6.2–42.8) malaria cases in VAB between January and December 2019.ConclusionsRegular larviciding is associated with a dramatic decrease in larval density and a modest but significant decrease in community-wide malaria incidence. Larviciding may provide a valuable complementary vector control strategy in commercial aquaculture settings across the Amazon.Graphical abstract

Selectivity of zooplanktonic preys in Heterobranchus longifilis larvae and fry

The present study was carried out to study the preferred prey in the larval and post-larval stages of Heterobranchus lonsifilis.Two hundred and forty larvae and fry of H. longifilis aged 2 to 23 days were stored in aquariums of 8 liters, fasted for 24 hours at the end of which they were fed to satiety with freshly collected zooplankton from fishponds. The day after feeding, the fish were euthanized and stored for stomach contents examination. The results showed that the zooplanktonic population density of the station ponds was 1356.73 individuals / L. This stand is composed of Cladocerans (455.85 individuals /l), nauplii (289.11 individuals / l), Rotifers (255.47 individuals / l), Copepodites (182.21 individuals / l) and Copepods adults (174.07 individuals /l). Furthermore, examination of stomach contents showed that adult Copepods were the most frequent and abundant prey category in stomach contents in terms of frequency of occurrence (66.7%) and numerical percentage (48.25%). In addition, these preys (adult copepods) constituted the preferred zooplankton prey in larvae and post-larvae of H. longifilis with an electivity index (E) equal to +0.5. Apart from the first size classes in which no prey has been observed in the stomach contents, the food preferences of H. longifilis larvae and fry do not vary with the size of the individuals. This study showed that adult copepods were the preferred zooplankton prey of H. longifilis larvae and fry.

Can shrimp farming wastewater negatively affect water quality and zooplankton community structure of a Neotropical estuary? A case study during a productive cycle of Litopenaeus vannamei

Aquaculture wastewater can influence various communities’ structures in both marine and freshwater environments. This study describes the zooplankton community structure and environmental variables in both Passos River estuary (Northeast Atlantic, Brazil) and commercial shrimp farming ponds associated with this estuary. Samples for water quality analysis and quantification and identification of zooplankton were taken during a shrimp culture cycle (July to September 2014) from eight sites (two across the main channel, downstream and upstream, and six shrimp farming ponds). The main water quality parameters showed difference between the shrimp farming ponds and the Passos River estuary – higher levels of total phosphorus and chlorophyll-a were observed in the shrimp ponds. The zooplankton structure at different environments was dominated by the copepods (53.3 to 83.7%) and rotifers (9.2 to 35.5%) but no significant difference was observed among the individual densities. Meanwhile, nutrients availability was a key for high plankton densities in shrimp ponds. These findings have suggested that wastewater from shrimp farming did not influence the zooplankton community on a Neotropical estuary on a short-time scale.

Hydroacoustics for density and biomass estimations in aquaculture ponds

The use of hydroacoustics is currently being studied and developed as a promising non-intrusive methodology to monitor and manage fish stocks in aquaculture farms. The main objective of this study was to develop an acoustic method for the estimation of fish density and biomass in inland aquaculture farms and test the accuracy and precision of the estimates with real data provided by the company. The study was conducted in sea bass (Dicentrarchus labrax) production ponds located in Seville (Southern Spain). A Simrad EK60 echosounder with two split-beam circular transducers operating simultaneously at 200 kHz was used for hydroacoustic surveys. Two different hydroacoustic designs were considered: central trajectories and zigzag trajectories. The accuracy and precision of the estimates were examined in order to select the best sampling design. Due to a non-homogeneous fish distribution in the pond caused by the avoidance behaviour, as a response to the sampling disturbance presented by fish, acoustic density and biomass were corrected by applying sampling theory according to the probability of fish detection. When density and biomass were corrected, the estimates became highly accurate and precise with respect to real data, which confirms that the proposed method is adequate. Similarly, acoustic estimates of fish weight were highly in agreement with real data, due to the use of specific equations developed “in situ” for the study. Although no significant differences were recorded in the density and biomass estimates with regard to the trajectory used (central vs. zigzag), it was observed that the most accurate agreement and precision were always obtained in central trajectories. Therefore, central design is proposed as the most appropriate design for hydroacoustic measurements in inland ponds. The results obtained in this study provide estimates of density and biomass that accurately match the real data, supporting the use of hydroacoustics as a potentially valid tool to manage inland aquaculture farms.

Keep your natural enemies close – native predators can maintain low mosquito densities in temporary ponds in a malaria expansion area in Northern Tanzania

Mosquitoes and the diseases they transmit are a global public health threat that affects most human populations. Mosquito abundances are strongly linked to the number of suitable larval habitats available. However, it is still not well understood how different land uses impact larval habitat quality in different parts of the world. We investigated links between land use practices and abundance of mosquito larvae in temporary ponds located in different land uses in a malaria expansion zone in Tanzania. Temporary ponds are often cited as important sources of mosquitoes but are also of substantial conservation concern being home to a unique fauna and flora. Often, they also have high socio-economic importance. Overall, encountered mosquito larval abundances were very low, both for the collected Anopheles gambiae s.l. and Culex quinquefasciatus. Although temporary ponds are important mosquito larval habitats in other parts of Africa, currently they are unlikely to be an important factor affecting the prevalence of mosquito borne diseases in the Manyara study region. Larval abundances in temporary ponds were higher in agricultural areas where more eutrophic conditions were found and minimal in residential areas. Overall, even though temporary ponds are often modified as rice paddies in the rainy season, they were in a good ecological condition and hosted a diverse assemblage of aquatic predators that likely prevented larval mosquitoes from reaching high densities. Maintaining this good condition by preventing pesticide and nutrient input as much as possible, can be important to prevent pond degradation that is likely to make these habitats more suitable for mosquitoes in the future.

Assessment of pond and integrated aquaculture (IAA) systems in six districts of Tanzania

Integrated agriculture and aquaculture systems (IAA) are well known for their ability to improve the overall farm productivity and profitability. This is through recycling of on-farm resources, such as nutrient rich fish pond water and agriculture remains that would otherwise be considered as wastes. The present study explores the existing and potential IAA systems in Tanzania. It also examines management strategies and their influence on fish yield and the economic returns between IAA and non-IAA fish farming. The study assesses farmer’s socio-demographic characteristics and their perception towards fish farming. The study was conducted through an on-site survey of 129 fish ponds owned by 89 farmers in six districts in Tanzania, involving 65 and 64 IAA and non-IAA ponds respectively. Results indicate that tilapia-vegetables is the most common type of IAA practiced by fish famers. Despite higher fish feed use and stocking density in non-IAA ponds, IAA ponds had an average fish yield of 2.46 t ha -1 , which was significantly (p<0.05) higher than the fish yield of 1.54 t ha -1 found for non-IAA ponds. IAA ponds had also 1.6 and 2.9 times higher (p< 0.05) revenue and net profit, respectively, than non-IAA ponds. Additionally, the net return from IAA ponds in an integrated system was significantly (p<0.05) higher than when practiced as stand-alone activities. IAA famers were more positive towards fish farming compared to non-IAA farmers. Thus, IAA systems should be promoted among small-scale farmers to cover for an increased fish demand and to improve food security.