Intelligent fish farm—the future of aquaculture

Aquaculture International - With the continuous expansion of aquaculture scale and density, contemporary aquaculture methods have been forced to overproduce resulting in the accelerated imbalance...     

Metal leaching and toxicity of denitrifying woodchip bioreactor outflow—Potential reuse application

The denitrifying woodchip bioreactor is designed to remediate nitrate-rich water, including those produced from aquaculture effluents. Reuse of treated bioreactor outflows in recirculating aquaculture would offer considerable water savings and valuable alkalinity recuperation. However, such bioreactors may leach detrimental wood-bound contaminants, preventing outflow reuse. To determine water reuse potential, woodchip media from two hardwood species (white ash, Fraxinus americana; Norway maple, Acer platanoides) were evaluated for 206 d under a range of operating conditions (start-up, steady-state, reducing conditions, and drying-rewetting cycles) for a spectrum of potentially harmful dissolved contaminants. Aerated outflows also were evaluated for acute and chronic toxicity to the biologically sensitive invertebrate Ceriodaphnia dubia. Dissolved metal leaching subsided within the first few weeks of operation, though initial concentrations of copper and zinc were detected at concentrations of concern. Elevated concentrations of tannins-lignin and total ammonia nitrogen were detected throughout the study and were influenced by operational phase. Acute toxicity was not generally detected, though chronic toxicity was observed during drying-rewetting cycles in the maple outflows. The measured toxicity was not correlated with water chemistry, indicating an additive effect of several toxicants. Overall, significant differences in outflow water quality between ash and maple wood species were negligible. Results indicated that bioreactor outflows may be applicable for aquacultural reuse, though reusing outflows immediately following start-up or restarting after a dry period would not be recommended.     

Start-up of a “zero-discharge” recirculating aquaculture system using woodchip denitrification,constructed wetland,and sand infiltration

Recirculating aquaculture systems (RAS) discharge management limits the development of the aquaculture sector, because RAS do not automatically result in low nutrient emissions. Research has helped develop discharge management systems such as wetlands and woodchip bioreactors that have been adopted by Danish commercial model trout farms. To further develop the Danish concept, we have modelled and built a novel “zero-discharge” recirculating aquaculture system with an annual capacity of approximately 14 tonnes. The aim of this paper is to describe the entire concept and present the results from the start-up phase of the whole system. The concept includes the treatment of RAS effluent (overflow and sludge supernatant) using a hybrid solution of a woodchip bioreactor, constructed vertical wetland, and sand infiltration. Using this three-step process, the nitrate, phosphorus, and organic matter effluent are decreased to acceptable levels to reuse the water in the RAS process reducing the need for new raw water. In the first nine months of operation, a water treatment field was used as an end-of-pipe treatment to ensure the water was safe to recirculate for fish. During the winter, the water temperature dropped to 2.7 degrees in the sand filter, but the frost did not reach the water levels in any of the treatment processes. It therefore appears that a hybrid solution can operate sufficiently even in winter conditions. In the first year of operation, a woodchip bioreactor can remove 97 % of the nitrate, although the slow start-up of the RAS caused the bioreactor to be N-limited. On average, 79 % and 92 % of the inflow phosphate concentration was removed in the woodchip bioreactor and the entire hybrid treatment field respectively. The wetland and sand filter removed organic matter sufficiently (35 %), but because of the longer than designed actual water residence, it leached from the bioreactor more than was expected. Further experimentation is needed to identify the financial applicability and performance during higher feeding rates.     

Identifying invasive fish species threats to RAMSAR wetland sites in the Caspian Sea region—A case study of the Anzali Wetland Complex (Iran)

Risk screening tools play a crucial role in identifying potential high-risk non-native (NN) fish species. In this study, potentially invasive NN fish species in the Anzali Wetland Complex (AWC), which is located on the south coast of the Caspian Sea (Iran), were identified using the Aquatic Species Invasiveness Screening Kit (AS-ISK). Twenty-nine freshwater fish species were screened of which 13 exist in the AWC and 16 in close proximity to it (“horizon” species). Receiver operating characteristic curve analysis showed that AS-ISK could discriminate reliably between non-invasive and invasive fish species for the AWC. Mean threshold scores were 3.25 for the Basic Risk Assessment (BRA) and 11.75 for the BRA + CCA (BRA + Climate Change Assessment), and these, respectively, classified 89.7% and 86.2% of the species as high risk. The CCA resulted in an increase in the BRA scores for 86.2% of the species, suggesting the need to account in future NN species management for a likely increased invasiveness of those species under future climate conditions. These results suggest that AS-ISK could prove an effective tool for identifying potentially invasive NN freshwater fishes in other wetlands of the Caspian Sea basin.     

Can Mediterranean cephalopod stocks be managed at MSY by 2020? The Balearic Islands as a case study

According to the Common Fisheries Policy (CFP), all European fish stocks should be brought to a state where they can produce at MSY by 2015 wherever possible or by 2020 at the latest. Despite the high socio‐economical importance of cephalopods in the Mediterranean and the increased availability of stock assessments during the recent past, only few European cephalopod stocks have been assessed to date. Surplus production models were applied to analyse the exploitation state of octopus and cuttlefish stocks from the Balearic Islands (western Mediterranean) to estimate how far away they were from the MSY target established by the CFP using a long‐term data series (1977–2013). The stocks were overexploited (cuttlefish) or about to be overexploited (octopus) during the late 1970s; this state remains even now and will only recover from overexploitation by 2020 if severe measures are taken.     

Does marine fish farming affect local small‐scale fishery catches? A case study in the NW Mediterranean Sea

Fish farms have been shown to aggregate large numbers of wild fish in their surroundings. Although little is known about how this affects the local fishery, two hypotheses have been put forward; a trapping and a protecting effect on wild fish. This study provides the first monitoring of commercial and recreational fishing activity at a fish farm. We assessed the effect on the small‐scale fishery analysing the differences between fishing in farm proximity and away from the farm (in terms of catch rate, income and catch composition). Moreover, we estimated the biomass removal from fishing activities by farm employees inside the farm. The study was conducted from January 2011 to June 2012 at a Gilthead seabream farm in the NW Mediterranean. The findings revealed a relevant amount of commercial and recreational fishing effort in farm proximity. Yet, the results showed no benefit or difference of fishing in close proximity to the farm compared with areas away from the farm. Thus, we conclude that farm‐aggregated fish are protected from the commercial fleet by the farm leasehold area, but remain vulnerable to hidden fishing practices inside the farm, where farm employees harvest more than 4 t of wild fish annually.     

Profiles of sex steroids, fecundity and spawning of a migratory characiform fish from the Paraguay–Paraná basin: a comparative study in a three-river system

This study investigated for the first time the reproductive biology of Prochilodus lineatus in a system of rivers in southeastern Brasil, relating it to the role of tributary rivers in the reproductive success of this important commercial fish in the Upper Paraná River basin, where a cascade of hydroelectric dams were deployed. Specimens were caught bimonthly in three river sites: (S1) Grande River, downstream from the Porto Colômbia dam; (S2) Pardo River; and (S3) Mogi Guaçu River. Sex steroid plasma levels, fecundity, follicular atresia, oocyte diameter and gonadosomatic index (GSI) were compared among sites. In S1, fish exhibited changes in the reproductive parameters: lower GSI, oocyte diameter and fecundity and higher follicular atresia index, when compared to S2 and S3. Frequency of maturing fish was higher in S3 and spawning was only registered in S3. In sites S2 and S3, plasma concentrations of testosterone and 17β-estradiol in females and testosterone in males showed wide variations following gonadal maturation. Fish from S1 showed few significant variations in sex steroid concentrations throughout the gonadal cycle. These results indicate that P. lineatus does not reproduce in Grande River (S1), but probably uses the Pardo River (S2) as a migratory route towards the Mogi Guaçu River (S3) where they complete gonadal maturation and spawning. Our findings contribute for understanding the reproductive biology of P. lineatus and to highlight the importance of tributaries in impounded rivers as a favourable environment for migration and spawning of fish.     

Chironomid farming — A means of recycling farm manure and potentially reducing water pollution in Hong Kong

In Hong Kong, chironomid larvae are grown on chicken manure. The larvae are used in large quantities as live food for aquarium fish and carnivorous fish fry in fish culture. In this survey, the culture technique and yield of chironomid farming were studied. The technique is simple: at temperatures of 15–30°C the yield is about 140 kg in a 675 m² field per cycle of 50 days. Since a large quantity of chicken manure, about 1440 kg, is consumed in each cycle, and there is also the possibility of using other farm wastes to grow chironomid larvae, this highly profitable chironomid farming may be developed to reduce the problem of stream pollution due to the farm wastes.     

A predator–prey model for evaluating the spatial behaviour of fishing fleets: a case study of the red grouper Epinephelus morio fishery of Yucatan,Mexico

A predator–prey model was applied to the red grouper Epinephelus morio fishery from Yucatan, Mexico, with the aim of understanding the spatial behaviour of a mid-sized fishing fleet. The heterogeneity of the environment was considered, and different habitat quality levels were determined to address environmental differences. The behaviour of the fleet was also evaluated based on a simulation of restricted fishing areas (RFA). The model was applied utilising 5 years of information on catch and fishing effort (1973–1977). Four levels of habitat quality were defined (low, medium, high and exceptional). The total costs and revenue for a fishing expedition in the areas of exceptional habitat quality were higher due to their location farthest from the base port. The fleet was most efficient during the winter at locations in the eastern continental shelf, with the number of these areas clearly decreasing in the autumn. The model simulation of the RFA showed a total revenue reduction of 7–27 % in scenarios of RFA for adult protection. When the RFA was implemented for the protection of juvenile fish, the total revenue was not reduced, indicating that this type of RFA might be a feasible management strategy for a sustainable fishery.     

What makes fish vulnerable to capture by hooks? A conceptual framework and a review of key determinants

Considerable time and money are expended in the pursuit of catching fish with hooks (e.g., handlining, angling, longlining, trolling, drumlining) across the recreational, commercial and subsistence fishing sectors. The fish and other aquatic organisms (e.g., squid) that are captured are not a random sample of the population because external (e.g., turbidity) and underlying internal variables (e.g., morphology) contribute to variation in vulnerability to hooks. Vulnerability is the probability of capture for any given fish in a given location at a given time and mechanistically explains the population‐level catchability coefficient, which is a fundamental and usually time‐varying (i.e., dynamic) variable in fisheries science and stock assessment. The mechanistic drivers of individual vulnerability to capture are thus of interest to fishers by affecting catch rates, but are also of considerable importance to fisheries managers whenever hook‐and‐line‐generated data contribute to stock assessments. In this paper, individual vulnerability to hooks is conceptualized as a dynamic state, in which individual fish switch between vulnerable and invulnerable states as a function of three interdependent key processes: an individual fish's internal state, its encounter with the gear, and the characteristics of the encountered gear. We develop a new conceptual framework of “vulnerability,” summarize the major drivers of fish vulnerability, and conclude that fish vulnerability involves complex processes. To understand vulnerability, a shift to interdisciplinary research and the integration of ecophysiology, fish ecology, fisheries ecology and human movement ecology, facilitated by new technological developments, is required.     

Evidence of improved water quality and biofilm control by slow sand filters in aquaculture – A case study

A rapid sand filter (RSF, 12 m³ m⁻² h⁻¹) and a rapid sand filter followed by slow sand filter (RSF-SSF, 0.1 m³ m⁻² h⁻¹) were compared to investigate whether the biological activity in the RSF-SSF would improve turbidity reduction and control of biofilm growth in seawater aquaculture of juvenile dusky grouper over a 31 days test period. The RSF-SSF combination produced water with lower turbidity than RSF, turbidity breakthroughs in RSF were effectively abated by SSF. Microbial growth potential (MGP) measured by a growth assay with Pseudoalteromonas spongiae in samples filtered through 0,2μm membranes was significantly smaller in SSF filtrate (MGP, 3.2 ± 0,1 logCFU) than in RSF filtrate (3.9 ± 0,6 logCFU). Turbidity in fish tanks fed with RSF-SSF and RSF effluent remained below 1 NTU and 6 NTU, respectively, inspite of the large amount of food not consumed by the fish and of the tanks remaining open to the atmosphere. Surface biofouling on PVC samples was assessed by protein and carbohydrate analysis. It was less pronounced on bottoms of tanks operated with RSF-SSF treated water but similar on tank walls for both types of water. Carbohydrates were present in much larger quantities than proteins in bottom biofilms, but the opposite occurred in wall biofilms. Diatoms were dominant in RSF but not in RSF-SSF tank biofilms. Dusky grouper survival and growth was similar for the two types of water. The benefit of reduction of microbial growth potential achieved in SSF pretreatment was successfully captured in lesser tank surfaces biofilm colonization and by lower water turbidity in the tanks.     

Do cannibalistic fish possess an intrinsic higher growth capacity than others? A case study in the Asian redtail catfish Hemibagrus nemurus (Valenciennes, 1840)

This study relied on the day‐by‐day analysis of bioenergetics and prey size preference in larvae and juveniles of Hemibagrus nemurus selected at random, held in isolation (28.5°C, 12L:12D) and feeding ad libitum on conspecifics [21 fish, 12–46 mm total length (TL), dry mass (DM) of 1–145 mg]. Several traits concur to make young H. nemurus highly cannibalistic: (1) high predation capacities (largest prey = 88% and 70% TL in fish of 8 and >40 mm TL, respectively), (2) opportunistic feeding behaviours with no marked size preference and (3) an unusual combination of high food intake (>100% DM at 1 mg DM) and very high gross conversion efficiency (>0.70). A growth model was constructed from the top performances of fish feeding maximally (16 of 21 fish) and indicated that the risk of cannibalism would be high and permanent except for meal frequencies over five daily meals. Cannibals emerging spontaneously under communal rearing (6 fish L^?1, three daily meals) grew more slowly or just at the same rate as predicted by the growth model constructed from siblings selected at random. This indicates that the individuals that become cannibals do not possess higher intrinsic capacities for growth than others.     

Wealth and welfare? Can fisheries management succeed in achieving multiple objectives? A case study of Lake Victoria,East Africa

Fisheries policies often pursue multiple objectives, which may, in some instances, be in conflict or competition with each other. It may not be possible, for example, to create or maintain employment and generate increasing volumes of revenue for government whilst also sustaining stocks and biodiversity. Two approaches to fisheries management, one focused on capturing wealth and limiting access and the other on maintaining access for employment and providing community development and welfare, present contrasting policy advice, with different points of emphases and objectives. This article examines the case of Lake Victoria, where the three main commercial fisheries are seen to contribute to different objectives for the lake's fisheries. Insights from the debate between wealth‐based and welfare‐based approaches to fisheries management provide a framework for the analysis of fisheries policy and practice on the lake. From the analysis, it is concluded that whilst there is much rhetoric in support of a wealth‐based approach, this has not been followed through in implementation, reflecting the lack of political support for new taxation and limiting access. The welfare functions of the fisheries are significant, but could be substantially strengthened through greater investment in the provision of services to fisheries communities. The approaches are not mutually exclusive, but pursuing wealth‐based management must support livelihoods, employment and development, as well as fisheries management objectives. Without the incorporation of welfare objectives, fisheries policies will not be politically accepted or fully implemented, suggesting the need for a balance between wealth and welfare objectives and measures.     

Quantifying current and future risks of invasiveness of non-native aquatic species in highly urbanised estuarine ecosystems—A case study of the River Neretva Estuary (Eastern Adriatic Sea: Croatia and Bosnia–Herzegovina)

Biological invasions are a major driver of global environmental change as invasive non-native species can exert severe environmental impacts on invaded ecosystems. Estuaries are especially vulnerable to biological invasions, which in highly urbanised areas are further facilitated by introduction pathways linked to commercial activities. This study provides a risk screening of non-native invasive species for the highly urbanised River Neretva Estuary (Eastern Adriatic Sea: Croatia and Bosnia–Herzegovina). In total, 12 species of non-native aquatic organisms were identified and screened for their invasiveness with the Aquatic Species Invasiveness Screening Kit. Of these species, eight were classified as carrying a high risk of invasiveness under current climate conditions and nine under future climate conditions. Amongst the high-risk species, blue crab Callinectes sapidus has already caused impacts in the risk assessment area, where it also represents an important economic resource. The “horizon” species Pacific oyster Crassostrea gigas and Manila clam Ruditapes philippinarum also carried a high risk of invasiveness, which for the latter species applied under predicted global warming. The present findings will contribute towards preventative management and control measures for the conservation of the natural ecosystem of the River Neretva Estuary whilst accounting for aquatic farming demands.     

Does orientation of raft helps in augmenting yield during lean period?: A case study of Gracilaria edulis cultivation in open sea by vertical raft alignment along the south-eastern coast of India

The food grade agar in India has been almost exclusively obtained from Gracilaria edulis, but the industrial production overwhelmingly relies on exploitation of natural resources. United Nations efforts through Food and Agriculture Organization under Bay of Bengal Program highlighted the necessity of undertaking commercial farming of this species along Indian coast for socio-economic benefits. The pilot-scale experiments established viability of large-scale cultivation by floating raft method. Nevertheless, drastic reduction in yield and quality during summer months due to enhanced sedimentation and severe epiphytism is found to be a major hindrance. Altering the positioning of rafts from horizontal to vertical alignment improved the growth and yield under open sea condition at two different locations along south east coast of India. The average yield in horizontal raft was found to be 3.08 ± 0.61 kg fr wt raft⁻¹ with corresponding DGR of 1.87 ± 0.63% day⁻¹ while same in case of vertical rafts was 13.76 ± 3.86 kg fr wt raft⁻¹ and 5.00 ± 0.5% day⁻¹ in Gulf of Mannar under 45 days growth cycle. The corresponding values along Palk Bay were 2.98 ± 0.52 g fr wt raft⁻¹ and 1.38 ± 0.42% day⁻¹ for horizontal raft and 13.02 ± 6.06 kg fr wt raft⁻¹ and 4.14 ± 1.18% day⁻¹ for vertical raft. ANOVA clearly indicated that raft position significantly influenced the biomass yield and DGR at Palk Bay (F = 75.77; F = 112.81) as well as Gulf of Mannar (F = 27.21; F = 59.16) at p = 0.001. The increment of 1.9–2.6% in fresh weight of individual frond was reported in vertically aligned rafts. The computational fluid dynamics (CFD) based unsteady numerical simulations have confirmed that vertical alignment of raft facilitates relatively free movement of water due to which sedimentation and epiphytism are either minimised or eliminated. Thus these studies can help us to deduce important conclusions pertaining to management of sustained commercial cultivation of this alga in Indian waters.     

Is it possible to differentiate between environmental and fishery effects on abundance‐biomass variation? A case study of blackspot seabream (Pagellus bogaraveo) in the Strait of Gibraltar

We assessed the potential for simulation and modelling of the blackspot seabream (Pagellus bogaraveo) population in the Strait of Gibraltar to discriminate the environmental effects of fishery impacts. A discrete biomass–abundance dynamic model was implemented to obtain a simulated monthly time series of blackspot seabream biomass. On this simulated time series, autoregressive integrated moving average (ARIMA) models were fitted. The best ARIMA fit provided a significant correlation of 0.76 and persistence index higher than 0.85. The proportion of variance non‐explained by the ARIMA models was correlated with a time series of sea surface temperature (SST) and North Atlantic Oscillation (NAO). The analysis of global, annual and winter correlation between the proportion of variance not explained by the ARIMA models and environmental variables showed that significant associations were not detected over the full time series. Our analysis therefore suggests that overexploitation is the main factor responsible for the commercial depletion of blackspot seabream in the Strait of Gibraltar.     

Tub gurnard Chelidonichthys lucerna L.: a new fish species suitable for farming? First answers evaluating the growth of juveniles reared at different stocking densities,welfare and fillet quality

A trial was conducted to evaluate the growth performance and survival of Chelidonichthys lucerna. A total of 13 352 180‐days old juveniles (5.5 ± 2 g; 5 ± 1 cm) were reared at two different densities (A‐EXP = 68 fish m^?3; B‐FFA = 15 fish m^?3) in eight tanks (four tanks per group) for 360 days. The welfare status and meat quality of fish were evaluated for the A‐EXP and B‐FFA groups in comparison with wild‐caught fishery gurnard (C‐WID). The survival rate was high for both A‐EXP (79%) and B‐FFA (93.5%). B‐FFA fish had the highest specific growth rate (1.16 vs. 1.07; P < 0.05), and were heavier than A‐EXP fish (321 ± 40 g vs .239 ± 44 g; P < 0.01). Rearing conditions did not affect blood metabolites, except for glucose concentrations, which were higher in C‐WID (P < 0.05). The meat quality traits showed that reared groups were fatter (2.8–3.2%) than C‐WID (0.94%); total n‐3 fatty acids (19.02–19.26%) were lower in reared groups than C‐WID (29.99%); and EPA + DHA were similar in all groups (15.1–16.61% vs. 27.99%). Despite the good growth and survival, the final mean weight was below that requested by the market (400–500 g). Future research efforts should focus on reducing the feed conversion rate (3:1).     

Assessment of perceived farming risks,communication of risk management practices,and evaluation of their efficiency in Pacific white shrimp (Penaeus vannamei) farming—a survey-based cross-sectional study

Aquaculture International - Pacific white shrimp (Penaeus vannamei) farming is an important commercial aquaculture production system contributing substantially to the economic and societal...     

Are brown trout Salmo trutta fario and rainbow trout Oncorhynchus mykiss two of a kind? A comparative study of salmonids to temperature‐influenced Tetracapsuloides bryosalmonae infection

Proliferative kidney disease (PKD) of salmonids caused by Tetracapsuloides bryosalmonae causes high mortalities of wild brown trout (Salmo trutta fario) and farmed rainbow trout (Oncorhynchus mykiss) at elevated water temperatures. Here the aim was to compare the temperature‐dependent modulation of T. bryosalmonae in the two salmonid host species, which display different temperature optima. We used a novel experimental set‐up in which we exposed brown trout and rainbow trout to an identical quantified low concentration of T. bryosalmonae for a short time period (1 hr). We followed the development of the parasite in the fish hosts for 70 days. PKD prevalence and parasite kinetics were assessed using qPCR. Exposures were performed at temperatures (12°C and 15°C) that reflect an environmental scenario that may occur in the natural habitat of salmonids. T. bryosalmonae infection was confirmed earliest in brown trout kept at 15°C (day 7 post‐exposure) while, in all other groups, T. bryosalmonae was not confirmed until day 15 post‐exposure. Moreover, significantly greater infection prevalence and a faster increase of parasite intensity were observed in brown trout kept at 15°C than in all other groups. These results indicate that PKD is differentially modulated by water temperature in related host species.