Cage Fish Farming Research Articles

Zooplankton community resilience and aquatic environmental stability on aquaculture practices: a study using net cages

Fish farming in net cages causes changes in environmental conditions. We evaluated the resilience of zooplankton concerning this activity in Rosana Reservoir (Paranapanema River, PR-SP). Samples were taken near the net cages installed at distances upstream and downstream, before and after net cage installation. The resilience was estimated by the decrease in the groups' abundance after installing the net cages. The zooplankton community was represented by 106 species. The most abundant species were Synchaeta pectinata, S. oblonga, Conochilus coenobasis, Polyarthra dolichoptera and C. unicornis (Rotifera), Ceriodaphnia cornuta, Moina minuta, Bosmina hagmanni and C. silvestrii (Cladocera) and Notodiaptomus amazonicus (Copepoda). The resilience of microcrustaceans was affected in the growing points as this activity left the production environment for longer, delaying the natural ability of community responses. Microcrustaceans groups, mainly calanoid and cyclopoid copepods, had a different return rate. The net cage installation acted as a stress factor on the zooplankton community. Management strategies that cause fewer risks to the organisms and maximize energy flow may help in maintaining system stability.

Exploring consumer’s preferences for farmed sea bream

Sea bream (Sparus aurata) production plays a significant part in Italian aquaculture, contributing to almost 18% of national pisciculture sales revenue. In recent years, Italian firms faced higher competition from countries with lower production costs. This prompted responses toward both cost reduction and product differentiation. The objective of this study was to investigate the preferences of Italian consumers for sea bream from fish farms, with a focus on aspects of product differentiation as gleaned from the analysis of the market situation: price, product origin, type and place of fish farming, and, in particular, type of feed. Data were collected with a consumers’ survey using personal interviews conducted on a questionnaire that included a choice experiment. Consumer preferences were analyzed with choice models based on stated preference data. The models made it possible to evaluate the potential of products with different combinations of attributes for which there is currently no market information available. In particular, the country of origin emerged as an important element of consumer choice, and to a lesser degree, organic certification and fish farming in marine cages also play a relevant role and may command a price premium.

象山港南沙岛不同养殖类型沉积物酸可挥发性硫化物的时空分布

Xiangshan Bay,located on the east coast of China,is a semi-enclosed bay with slow rate of water exchange.Nansha Bay,lies in the middle of Xiangshan Bay,is an important fish cage farming area.This paper presented the results of the seasonal and spatial distribution of acid volatile sulfide(AVS) in sediments from three different mariculture areas including seaweed culture area,shellfish culture area and fish cage culture area in Nansha Bay in 2007.The results revealed that AVS content in the whole investigation region ranged from 0.01 to 30.03 μmol/g,the average value was 3.75 μmol/g.The mean value of AVS in shellfish culture area,seaweed culture area,fish cage culture area and the control area were 1.03,0.64,5.06,and 0.70 μmol/g,respectively.Although there was no significant change of AVS in surface sediment,significant difference of AVS in columnar sample(0—15cm) was found among winter,summer,spring and autumn,with the average value 3.48,3.05,8.31 and 6.57 μmol/g in,respectively.The value of AVS increased with the sediment depth,and reached the maximum in 6 to 9 centimeter,especially in summer and autumn.Cluster analysis showed the AVS distribution in the sediment of Nansha Bay could be divided into 3 categories: central cage area(S10) and surrounding cage area(S12 and S13);cage culture area(S6,S7 and S14) far away from central cage area;shellfish culture area(S1),algae culture area(S2) and control area(S5).The average values of AVS in different categories were 7.34,2.62 and 0.75 μmol/g,respectively.Overall,the AVS content was highest in central cage area and gradually reduced with the distance along the central cage area.The impact of fish cage farming on AVS mainly concentrated in the area within 200 m from fish cages and influence slightly far away from 500m.

Benthic metabolism and nitrogen transformations affected by fish cage farming in the tropical Nha Phu estuary (Vietnam)

Effects of organic-waste loading from fish farming on benthic metabolism and nitrogen (N) cycling were studied in the tropical Nha Phu Estuary, Vietnam. The loading of fish excreta and feed waste enhanced benthic oxygen (O2) uptake two times and total carbon dioxide (TCO2) release three times, compared with the reference station. NH4+ was the major form of released N, comprising 94–100% of dissolved inorganic N (DIN) flux below and near fish cages. Only 3% and 1% of organic carbon (OC) and organic N (ON) deposited from the fish farm was degraded in the sediment, whereas the rest was dispersed to adjacent areas via tidal currents or buried into the sediment. Coupled nitrification–denitrification were almost 0 under fish cages but increased at distances greater than 10 m from fish cages. Consequently, biologically available N was not removed permanently near fish cages as the excess N deposited under cages were mineralised and released as DIN. The nutrient efflux could therefore potentially be a source for pelagic primary production in the vicinity of cages. However, the water currents and low water residence time may have distributed and diluted the nutrient effect of cages to the entire estuary and the adjacent ocean.

Mortalities of sea-cage salmon ( Oncorhynchus tshawytscha) due to a bloom of Pseudochattonella verruculosa (Dictyochophyceae) in Queen Charlotte Sound, New Zealand

Over a 6 day period in mid winter (June) 2010 about 200 tonnes of Chinook salmon ( Oncorhynchus tshawytscha) on a sea-cage farm at Ruakaka Bay, Queen Charlotte Sound died as a result of exposure to a bloom of the dictyochophyte Pseudochattonella verruculosa. The alga was isolated and its identity confirmed by morphology and large subunit ribosomal DNA sequencing. Cells densities of P. verruculosa over several tens of thousands of cells per litre were sufficient to cause fish mortalities. The bloom originated in the inland reaches of the sound in the Grove Arm and the farm was located near its seaward extension. Fish were affected and recovered as the bloom front moved on and off the farm site under the influence of tidal currents. Before the bloom reached its peak (at about 1.0 × 10 5 cells L −1) the farm was relocated to a site outside the affected area where surviving fish quickly recovered. The bloom took place when day length and seawater temperatures were near their annual minimum (9 h and 12 °C respectively), and after its peak it was rapidly displaced by the in situ development of a diatom bloom dominated by Skeletonema costatum. The P. verruculosa bloom arose after several weeks of persistent rainfall. This may have assisted in the development of a circulation pattern that led to the movement of increasingly buoyant, relatively warm, nutrient-enriched bottom water into the Grove Arm, shoaling to shallow depths at the head of the inlet. The high productivity of waters in this area at the time is believed to have been largely driven by this mechanism. Larger size (∼3.5 kg) fish were mainly killed by the bloom and examination of affected salmon tissues showed pathologies in the liver and kidneys. There are ambitious plans for the expansion of sea cage fish farming in New Zealand and this event is a timely reminder of the hazard these events pose to sea cage fish farming operations.

Persistent organic pollutants and trace metals in sediments close to Scottish marine fish farms

The global demand for aquatic food products is increasing and the aquaculture industry is expanding as it strives to meet this increasing demand. There are concerns about the environmental impact of aquaculture to the seabed close to fish-farm cages, including potential effects from persistent organic pollutants and trace metals, which may come from the feed or anti-foulants on the cages. To determine if this could be a problem in Scotland, three main aquaculture areas were examined; Western Isles, North-West Coast of Scotland and the Shetland Isles. Samples of sediment were collected from various sea lochs in these areas in 2005 and 2006 and concentrations of persistent organic pollutants (polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs)) and trace metals (copper (Cu) and zinc (Zn)) were determined. Concentrations of PCBs were below the EAC (environmental assessment criteria) for all bar one congener in one sample, and below the BAC (background assessment concentration) for most. PBDE concentrations in the sea lochs are comparable with those found at remote sites around Scotland and comparable with the lower end of concentrations found in the more industrialised Firth of Clyde. Although slightly elevated Cu and Zn concentrations were measured in sediments from < 330 m from some farms, concentrations in sediments outwith 25 m from any farm are below those that cause benthic effects. Only the farms in Loch Shell, Loch Greshornish and Loch Kishorn had concentrations for Cu and Zn which might cause adverse affects in the environment, and all of these samples were from within 25 m of the cages. Therefore it was concluded that any impact on the environment from organic pollutants or trace metals is of a local nature.

Do benthic biofilters contribute to sustainability and restoration of the benthic environment impacted by offshore cage finfish aquaculture?

Benthic biofilters were deployed under a cage fish farm and in two reference locations to assess the influence of the farm on the biofilters and the surroundings, as well as to verify the usefulness of this technology as a mitigation tool. The biofilters underneath the farm recruited a fouling community practically identical to that of the control biofilters, which included a variety of trophic strategies. The former showed a higher 15N enrichment, indicating that fouling beneath the farm was benefiting from the farm waste. The waste retention efficiency was low (0.02gNm−2month−1) beneath the farm. Benthic biofilters aggregated demersal wild fish around and within them. Pelagic wild fish also frequently used the biofilters beneath the farm, forming compact shoals around them. The increased complexity of the habitat below the fish farm enhanced biodiversity, but this improvement did not lead to the recovery of the sediments around the biofilters.

Influence of fish cage farming on water quality and plankton in fish ponds: A case study in the Rift Valley and North Shoa reservoirs, Ethiopia

The potential impact of Nile Tilapia ( Oreochromis niloticus) cage culture on water quality and pelagic community composition was investigated in two Ethiopian small water bodies, one located in the highlands (Yemlo) and the other in the Great Rift Valley (Allage). This study was designed to assess the difference between the cages and open water in relation to those water quality changes attributable to intensive inputs of fish waste and left-over fish feed. All physico-chemical water quality parameters including inorganic nutrients varied temporally, coupled with dry and wet periods. The reservoir's trophic state ranged from eutrophic to hypereutrophic, with a strong correlation between chlorophyll- a and total phosphorus. The phytoplankton community was dominated by Cyanobacteria (84% of total phytoplankton abundance), in particular by Anabaenopsis sp. in Allage reservoir, whereas Chlorophyta (70%), with Pediastrum simplex as the dominant taxon, prevailed in Yemlo reservoir. A total of 23 zooplankton taxa were recorded during our sampling; rotifers were the richest group with 14 taxa distributed in 6 genera, followed by cladocerans represented by 6 taxa (5 genera) and copepods by 3 taxa (1 genus). Dissolved inorganic nutrient concentrations and other physical parameters showed no significant differences between the cages and open water. The exceptions were dissolved oxygen and ammonium nitrogen, which were lower and higher in the cages, respectively. For the whole study period of 240 days, the mean net weight and daily growth rate per fish were 183.3 g and 1.1 g d − 1 , respectively.

Small tropical reservoirs and fish cage culture: a pilot study conducted in Machakos district, Kenya

The findings of this study provide useful insights into the key aspects of fish cage farming to be considered during setting and overall management of multi-purpose water resources so as to maximise their aquacultural potential. The study was conducted in Machakos District, Kenya, to characterise limnochemistry and algal composition of three small man-made reservoirs Ngeki, Ngei and Kavovi, used for cage culture of Nile tilapia (Oreochromis niloticus). In Ngeki, the open water was compared with areas in between the cages and significant differences in dissolved oxygen were found. For N, P and chlorophyll-a, no differences were noticed. In all the reservoirs, temporal variations were noticed for all parameters except NO3N and NH4N. Peak concentrations of nutrients occurred during the rainy season with lower values in the dry season (below detectable limits for SRP). All reservoirs were classified as hyper-eutrophic with a strong positive correlation between chlorophyll-a and TP. Algal abundances changed with season. Chlorophyta dominated at the start of the rainy season, while cyanobacteria prevailed at the onset of thermal stratification. Diatoms prevailed in the dry season but were notably absent in the rainy season. It was concluded that all the reservoirs are suitable for cage culture of Nile tilapia, but this should be undertaken with caution considering critical periods when anoxic conditions may occur.

Spat Settlement and Growth of Mediterranean Mussel (Mytilus galloprovincialis) in Fish Cage Farms in Southeastern Black Sea Coast

Spat Settlement and Growth of Mediterranean Mussel (Mytilus galloprovincialis) in Fish Cage Farms in Southeastern Black Sea Coast

Fish Farming Affects the Abundance and Diversity of the Mercury Resistance Gene merA in Marine Sediments

Microbes in sediments below fish farming cages are exposed to a variety of compounds used in aquaculture, such as antifoulants, antimicrobials and mercury. Here, we assessed the abundance of the mercury resistance gene merA in the sediment of four fish farms and four pristine sites using quantitative PCR, and at three fish farms and two pristine sites by constructing clone libraries and sequencing merA amplicons. The abundance of merA was consistently greater at fish farm sites than at pristine sites, and the merA phylotypes were different between fish farm and pristine sites. Mercury concentrations were too low to cause selection pressure and did not differ significantly among samples. The primers designed specifically for this study were capable of detecting two new potential merA clades.

Effects of cage fish farming on phytoplankton community structure, biomass and primary production in an aquaculture area in the middle Adriatic Sea

In this study, we investigated the physical, chemical and biological parameters of the water column at two stations under different trophic conditions during a 1-year period (from September 2005 to September 2006) in an aquaculture area. The investigation was performed monthly at a station inside the fish farm in Maslinova Bay (middle Adriatic Sea, Croatia) and at a control station located in the Hvar Channel in the vicinity of the farm. The results showed that the concentrations of dissolved nutrients were slightly enhanced at the farm station in comparison with the control station, although those differences were not statistically significant, nor were the differences in oxygen saturation recorded during the investigation period. As opposed to the chemical parameters, considerably higher deviations were recorded for biological parameters as demonstrated by a significant increase in phytoplankton biomass and primary production (measured in situ) at the farm station, particularly during the summer season. Phytoplankton community structure analysis showed that the phytoplankton composition at the farm was mostly determined by seasonal changes rather than by the influence of fish farming. In Maslinova Bay, no causal links were identified between increased biomass and the appearance of toxic species.

Physical–chemical measurements in the water column along a transect through a tilapia cage fish farm in Lake Malawi, Africa

The initiation of cage aquaculture in the shallow southeast arm of Lake Malawi has raised concerns about its possible impact on the surrounding environment and the highly diverse fish community. To evaluate the impact of the cage operation on the surrounding environment, observations were made over an annual cycle in 2007 at a production capacity of ~ 200 tonnes fish/year. Impacts of the cage wastes in the water column in the vicinity of the cages were minimal despite the substantial discharges from the cages. No significant differences were observed in concentrations of dissolved and particulate nutrients (ammonia, nitrate, phosphate, particulate C,N and P), chlorophyll, chlorophyll fluorescence, dissolved oxygen, total suspended solids, Secchi depths and extinction coefficient of photosynthetically active radiation between the cage site and the control stations upstream or downstream of the fish farm. Although sedimentation rates measured in traps were higher under the cages than at control sites, the sediment flux was a small percentage of total feeds added to the cages. Apparently cage wastes were efficiently dispersed by water currents which averaged 9.3 cm/s below the fish cages. Consumption of the wastes by wild fish species which aggregated around the fish cages and their movement in the vicinity of the cages also contributed to the dispersion of the cage wastes and served to dilute impact of the cages. In combination, these physical and biological processes reduced the immediate impact of the cage farming operation and must be considered in the siting of future cage farms.

A Spatial Analysis of Fish Farming in the Context of ICZM in the Bay of Izmir-Turkey

Cage fish farming is one of the fastest growing food industries, both worldwide and in Turkey. There are growing concerns about the manner of resolving the competing claims for the use of limited coastline and water body space. Matters connected with the siting of fish farming increase the need for the integrated coastal zone planning of aquaculture. This should be undertaken in collusion with other coastal stakeholders and with the cooperation of the government ministries that promote and regulate aquaculture development. In this study the integration and coexistence of fish farms is evaluated in the context of other activities in Izmir Bay. This study shows how different terrestrial and marine activities interact with each other, and that certain areas are subject to layers of multiple usages. One of the major sea users of the Bay, for example, is the fishery sector, which utilizes 850.4 km2 of a total surface area of Izmir's Bay of 960.4 km2. This overlaps with the 113.4 km2 that are used by marine transportation. Military zones encompass 63.1 km2 and fish farming utilizes only 1.23 km2. This study uses Geographic Information Systems (GIS) to build a spatial database that analyzes conflicting claims for integrating fish farming with other claimants. Clearly planned and properly managed fish farming development should be undertaken within a broader framework of integrated coastal zone management.

Effects of water flow velocity and fish culture on net biofouling in fish cages

The effects of water flow, fish feed and cage position on net biofouling was examined in a floating cage fish farm. Fouling of 16 mm mesh net panels suspended inside and outside net cages and exposed to different treatments were monitored weekly until net apertures were completely occluded by the fouling organisms (8 weeks). Results indicate a dramatic reduction in water flow velocity throughout the fish farm due to the cage units themselves and net biofouling. The reduced water flow (<10 cm s−1) inside net cages promoted rapid net biofouling, while rapid water flow outside the net cages (>25 cm s−1) kept the net fouling organisms at bay. Although fish rearing in net cages with inputs of commercial pellet feed increased sessile biofouling (222% higher than outside the net cages) and non-sessile biofouling (570% higher), the type of fish feed used did not significantly affect biofouling development. The study recommends that the geometry of serially arranged net cages, as commonly deployed in tropical tidal estuaries, be reconfigured to improve flow through in order to minimize the impact of fouling.

The fouling of fish farm cage nets as bioindicator of aquaculture pollution in the Adriatic Sea (Croatia)

A fouling assemblage (including density, species richness and diversity, and biomass) growing on netting of fish farm cages was investigated in Stracinska Bay--Location 1 and Peles Bay--Location 2 (Croatia) in order to test the efficiency of fouling as a bioindicator of organic pollution. A total number of 40 algal taxa in Location 1 and total number of 22 algal taxa in Location 2 were identified, with a dominance of opportunistic species (ESG II). We found domination of algal species over animal species and absolute dominance of Rhodophyta which are typical fouler in the Adriatic Sea. Low diversity and species richness with increase in value of the R/P index (occasionally higher than 6) were recorded in Location 2, indicating a certain impact of nutrient enrichment from fish culture facilities on a fouling community structure.

Fishing near sea-cage farms along the coast of the Turkish Aegean Sea

Summary This study reports on the yield of commercially important species captured intentionally around and under fish-cage farms using specific types of gear from both sea-cage farmers and artisanal fishermen, and to identify the species composition of these catches. The 2004–2008 research was carried out in 21 fish farms, randomly chosen along the coast of Izmir Province on the Aegean Sea. A total of 91 persons were interviewed, including directors, fishers from the fish farms and artisanal fishermen. The technical characteristics of a special trap used by some fish farmers were diagramed. Total wild fish catch quantities as well the species raised in the sea-cages were recorded. A total of 34 finfish and four invertebrate species were identified from the sea-cage farm fishery. Eight fish species according to the descending quantities raised were bogue (Boops boops), grey mullet (Mugil spp.), blackspot seabream (Pagellus bogaraveo), salema (Sarpa salpa), common two-banded seabream (Diplodus vulgaris), annular seabream (Diplodus annularis), striped seabream (Lithognathus mormyrus) and gilthead seabream (Sparus aurata). Mean quantities of wild fish caught from 2004 to 2008 in a sampled farm were 13 998 ± 210, 34 434 ± 482, 30 116 ± 529, 27 893 ± 429, and 32 366 ± 808 kg, respectively. There were significant differences between fish amounts and years (P < 0.05).

Post-tsunami rehabilitation of fish cage farms on the Andaman coast of Thailand

A post-tsunami rehabilitation of cage culture along the Andaman Sea coast of Thailand was carried out in five provinces (Ranong, Phang-nga, Krabi, Trang and Satun) from September 2007 to February 2008. Based on the survey conducted, the money compensated subsequently used to buy materials for cage re-construction and cage repair accounted for 28.1% of the total, and to buy seed, feed and chemicals for culture operations, 15.8%. A surprising finding is that 56.1% of compensated money was used for other purposes. The analysis showed that the quality and quantity of equipment, seeds and feeds invested in aquaculture farms were increased in comparison with the pre-recovery period. Importantly, the farm area, growth rate, amount of product and revenue were improved during the post-tsunami rehabilitation period. Additionally, the area and quality of houses, household consumption, household infrastructures, health care and education were also improved. The satisfaction level of cage farmers in regard to the recovery programs was high (weigh average index = 3.88). The results from this study showed that the net economic profit (NEP) achieved was 41,030.49 baht/crop (33.9 baht = 1 US$) for sea bass culture, while NEP for grouper culture was 59,529.98 baht/crop. The result from the present study indicated that the economic value of cage culture farms was profitable. However, the seed shortage, high cost of trash fish, disease outbreak and marketing were among key problems and constraints encountered. In this study, we also found that the knowledge about fish marketing and culture techniques was poor. Therefore, technical, marketing and financial support are required for the future.

The fate of organic matter derived from small-scale fish cage aquaculture in coastal waters of Sulawesi and Sumatra, Indonesia

To determine the fate of organic matter derived from fish cage aquaculture, carbon and nutrient cycling processes in waters and sediments, and water circulation, were examined at two fish cage farms of different size and utilizing different food types, on Sulawesi and Sumatra islands, Indonesia. Mass balance models of C, N and P were constructed to assess the pathways of waste utilization and dispersal. At the smaller farm in Sulawesi (64.5m2 cage area; 3t annual net production) using pelleted food, there was proportionally less waste (≈40% of total C input) than at the larger Sumatran farm (2432m2 cage area; 9t annual net production) using trash fish (≈70% of total C input) as food. At the small farm, the mass balance and hydrographic models indicated a maximum dispersal area of 1180m2, equivalent to 18 times the farm area. Within this area, 30% of total organic matter input (farm waste+fixed phytoplankton carbon) was buried in sediments with 30% mineralized in the water-column and 40% mineralized in the seabed. At the larger Sumatran farm, the models indicated a maximum dispersal area of 29 220m2, roughly 12 times the farm area. Within this area, 30% of total organic matter input (farm waste+natural pelagic input) was buried in sediments with 50% mineralized in the water-column and 20% mineralized on the seabed. There was some evidence of benthic enrichment at both farms, mostly as enhanced dissolved nutrient release, but sulfate reduction accounted for <25% of total C flux, and denitrification/ammonium oxidation accounted for only 4–17% of N lost from sediments. There was no clear evidence of impact with distance from the cages at either farm. Phytoplankton gross primary production accounted for 60–77% of the total organic input to the receiving environment, suggesting that the relative importance of fish cage wastes must be assessed against natural inputs of organic matter.

‘Ghost nutrients’ from fish farms are transferred up the food web by phytoplankton grazers

Several studies have failed to detect sig- nificant changes in chl a content of the water column in the vicinity of fish farms despite the large amount of nutrient wastes discharged into the marine envi- ronment. To trace the fate of these disappearing (or 'ghost') nutrients, experiments using dialysis bags deployed in situ along gradients of nutrient enrich- ment (at different distances from cage fish farms) were carried out at 2 coastal locations in the eastern Mediterranean. The productivity of the water column decreased with distance from the nutrient discharge point, as indicated by the chl a content found in the dialysis bags. However, comparison of the results from bioassays with and without grazer exclusion showed that grazing plays a key role in regulating phytoplankton biomass, keeping chl a at very low levels and effectively transferring nutrients up the food web. The fact that this type of response was found in otherwise oligotrophic conditions is proba- bly due to the structure of the phytoplankton com- munity in such areas, which is based on small cell- size primary producers that can be easily grazed on by planktonic ciliates.