Infectious pancreatic necrosis virus in fish by‐products is inactivated with inorganic acid (pH 1) and base (pH 12)

The aquaculture industry needs a simple, inexpensive and safe method for the treatment of fish waste without heat. Microbial inactivation by inorganic acid (HCl) or base (KOH) was determined using infectious pancreatic necrosis virus (IPNV) as a model organism for fish pathogens. Salmonella and spores of Clostridium perfringens were general hygiene indicators in supplementary examinations. IPNV, which is considered to be among the most chemical‐ and heat‐resistant fish pathogens, was reduced by more than 3 log in 4 h at pH 1.0 and pH 12.0. Salmonella was rapidly inactivated by the same treatment, whereas spores of C. perfringens were hardly affected. The results indicate that low and high pH treatment could be particularly suitable for fish waste destined for biogas production. pH treatment at aquaculture production sites could reduce the spread of fish pathogens during storage and transportation without disturbing the anaerobic digestion process. The treatment could also be an alternative to the current energy‐intensive steam pressure sterilization of fish waste to be used by the bioenergy, fertilizer and soil improver industries.     

Supplemental Feeding of Tilapia in Fertilized Ponds

The addition of feed to fertilized fish ponds was evaluated by adding feed alone, feed plus fertilizer, or fertilizer alone to nine ponds stocked with Nile tilapia Oreochromis niloticus . Two experiments were conducted. The first had 500 fish per 250 m² pond in 3 treatments: ad-libitum feeding; fertilizer only; or fertilizer and ad-libitum feeding. The second experiment had 5 treatments with 750 fish per pond ad-libitum feed only; fertilizer only; or 0.25, 0.50, and 0.75 satiation ration plus fertilizer. Ponds in Thailand were maintained for 155–162 d, during which chemical and physical properties were monitored. In experiment 1 tilapia growth was highest in feed only ponds, and lowest in fertilizer only ponds. Net yield did not differ significantly among treatments, due to variation in survival. In experiment 2, tilapia growth was lowest in fertilizer only ponds, intermediate in 0.25 ration ponds, and highest in 0.50, 0.75, and ad-libitum ponds. The latter treatments were not significantly different. Multiple regressions for each experiment indicated only 47–87% of the variance in growth was explained by feed and fertilizer input, while 52–89% of the variance in yield was explained by those factors. For both experiments combined, 90.3% of the variance in growth was explained by feed input, fertilizer input, alkalinity, and total inorganic nitrogen concentration. For yield, R ² was 0.888 and the regression included feed input, pH, and number of low dissolved oxygen events. Experiment 1 appeared to approach carrying capacity near the end, while no reduction in growth occurred in experiment 2 at higher fish density and biomass. Reductions in growth in experiment 1 were not correlated with declining water quality late in the grow out. Combinations of feed and fertilizer were most efficient in growing tilapia to large size (500 g) compared to complete feeding or fertilizing alone.     

High rate algal pond treatment for water reuse in a marine fish recirculation system: Water purification and fish health

Regardless of the degree of closure of a recirculation system, effluents are produced and replacement water is needed, which limits the possibility of locating a seawater production system away from the shoreline. At the Palavas Ifremer station, in the south of France, a High Rate Algal Pond (HRAP) was operated during several years to treat the effluent from a recirculating aquaculture system before reusing it. The effect of the HRAP-treated water on the recirculation system and on the fish was investigated and the optimal algae growing conditions were defined. The experiments were carried out in three rearing systems: one flow through, one recirculating and one recirculating with a HRAP. The water flow rate, temperature, pH and salinity conditions were similar in all systems.The effect of reusing the HRAP-treated water is very limited (1) on the functioning of the recirculation system and (2) on fish performance, but it allows a significant reduction of the dissolved inorganic nitrogen and phosphorus concentration in the rearing water. HRAP treatment reduced metal accumulation in muscle and liver of RAS fish, except for chromium and arsenic. All biomarkers presented no significant difference between systems, except for Superoxide Dismutase (SOD) and EROD, which showed a higher concentration in RAS and in both recirculating system respectively.     

Inactivation of koi‐herpesvirus in water using bacteria isolated from carp intestines and carp habitats

Since its first outbreak in Japan in 2003, koi‐herpesvirus (KHV) remains a challenge to the carp Cyprinus carpio L. breeding industry. In this study, inactivation of KHV in water from carp habitats (carp habitat water) was investigated with the aim of developing a model for rapidly inactivating the pathogen in aquaculture effluent. Experiments with live fish showed that, in carp habitat water, KHV lost its infectivity within 3 days. Indications were that inactivation of KHV was caused by the antagonistic activity of bacteria (anti‐KHV bacteria) in the water from carp habitats. Carp habitat water and the intestinal contents of carp were therefore screened for anti‐KHV bacteria. Of 581 bacterial isolates, 23 showed anti‐KHV activity. An effluent treatment model for the disinfection of KHV in aquaculture effluent water using anti‐KHV bacteria was developed and evaluated. The model showed a decrease in cumulative mortality and in the number of KHV genome copies in kidney tissue of fish injected with treated effluent compared with a positive control. It is thought that anti‐KHV bacteria isolated from the intestinal contents of carp and from carp habitat water can be used to control KHV outbreaks.     

Hydroponic horticulture using residual waters from Oreochromis niloticus aquaculture with biofloc technology in photoautotrophic conditions with Chlorella microalgae

Protein‐dependent aquaculture generates large amounts of nutrient‐rich residuals; a feasible way to develop sustainable production systems is to integrate Decoupled Aquaponic Systems (DAPS) with residual water bioprocesses, to combine Photoautotrophic Biofloc Technology (P‐BFT) aquaculture and hydroponic horticulture. This study describes the characteristics of residual water from Oreochromis niloticus aquaculture performed with P‐BFT inoculated with Chlorella microalgae, reared during the nursery (180 fish m³) and grow‐out (55 fish m³) phases. The experiment included five treatments: photoautotrophic BFT inoculated with Chlorella sp. (M), C. sorokiniana 2714 (CV), and C. sorokiniana 2805 (CS), and chemoautotrophic (Q) and heterotrophic (H) as controls. Elemental characteristics in liquid and solid residual fractions (15 macro‐ and micronutrients) were compared among treatments and against Hoagland & Arnon solution with hydroponics and used in Nutrient Film Technique (NFT) hydroponic horticulture including five plant species: lettuce (Lactuca sativa), pak‐choi (Brassica rapa subsp. chinensis), rocket (Eruca sativa), spinach (Spinacia oleracea) and basil (Ocimum basilicum). The physicochemical parameters were ideal for O. niloticus and plants. The relationship between N:P was ideal until weeks 16–22 in the photoautotrophic treatments, compared with hydroponic solutions. Micronutrient content was greater in the solid than a liquid fraction. The best BFT effluent regarding fish and plant growth was photoautotrophic treatments. Oreochromis niloticus BFT aquaculture in photoautotrophic mode using microalgae Chlorella inoculations provided residual water beneficial to hydroponic horticulture in DAPS located in coastal arid zones where freshwater is scarce, improving aquaculture performance and reusing water and nutrients.     

Rhodopseudomonas palustris in effluent enhances the disease resistance,TOR and NF‐κB signalling pathway,intestinal microbiota and aquaculture water quality of Pelteobagrus vachelli

The use of traditional bait and medicament in freshwater aquaculture exacerbates environmental pollution and leads to frequent occurrence of diseases. Effluent collected after Rhodopseudomonas palustris‐mediated wastewater treatment could be reutilized as microbial feeds, medicament and aquaculture water to culture Pelteobagrus vachelli. Therefore, a novel integrated system of wastewater treatment using effluent containing R. palustris that improves yield, increases disease resistance and enhances the quality of aquaculture water for P. vachelli culture was proposed and investigated. P. vachelli can grow well in effluent containing R. palustris (ER). The survival rate, yield and whole‐body composition of the ER group were all increased compared to those of the control group (CK). The biochemical (B vitamin) and other substances in the effluent of R. palustris enhanced the activity of proteases, amylases, lipases, alkaline phosphatase (AKP), acid phosphatase (ACP), phagocytic, superoxide dismutase (SOD) and catalase (CAT) by up‐regulating the expression of AKP, ACP, SOD and CAT genes. Theoretical analysis showed that biochemical substances regulated the expression of these genes and enzyme activities as stimulus signal, component and active centre. Moreover, R. palustris and biochemical substances improved the target of rapamycin (TOR) and nuclear factor kappa B (NF‐κB) signalling pathways and intestinal microbiota. Furthermore, R. palustris inhibited Aeromonas hydrophila, which increased resistance to fish diseases and promoted the growth of intestinal probiotics. Meanwhile, R. palustris in effluent also purified the quality of aquaculture water. Use of this technology simultaneously helped improve aquaculture water quality, reduce water pollution and wastewater discharge and increased the output and disease resistance of P. vachelli.     

Effluent and production impacts of flow-through aquaculture operations in West Virginia

In light of recent changes to federal regulatory requirements placed on the aquaculture industry, aquaculture operators must act proactively to maximize their production to meet demands, compete with new operations, and maintain compliance with effluent standards. As a result, water quality characterization was conducted at six anonymous facilities using flow-through design, rearing mostly rainbow trout (Oncorhynchus mykiss) that were selected based on various water sources, operation, size, and effluent treatment.

Average concentrations and mass loadings of regulated parameters were within regulatory limits and increased in direct proportion to the mass of fish reared. However, when comparing effluent pollutant concentrations and loads with West Virginia National Pollutant Discharge Elimination System (NPDES) permit limitations, the potential for increased production existed at each facility. Based on the current West Virginia NPDES limit of 30 mg/L for total suspended solids (TSS), each facility could increase production from 147 to 819%. However, with a more stringent TSS limitation of 5 mg/L net used in states in the western US, two facilities would have to reduce production from 37 to 44%, while the other sites could increase production from 19 to 170%. Consequently, the opportunity to increase production under any set of regulatory constraints was a function of annual fish production, legal requirements, and the implementation of effective effluent treatment processes.     

A Survey of Water Quality Characteristics of Effluent from Hawaiian Aquaculture Facilities

Ten water quality parameters were measured in influent and effluent water at 11 aquaculture facilities in Hawaii. The data were grouped into four categories based on the types of organisms cultured: freshwater fish, freshwater prawn, marine fish, and marine shrimp. Within each category, concentrations of most parameters were lognormally distributed and spanned one to two orders of magnitude. Geometric mean concentrations of suspended materials, total nitrogen, total phosphorus, and pigments were highest in effluent from freshwater prawn ponds and lowest in marine fish pond effluent. Nitrate/Nitrite and total ammonia concentrations were higher in fish pond effluent than in crustacean pond effluent. Parameter concentrations were generally higher in effluent than in influent water, with freshwater fish and prawn ponds exhibiting the greatest increases in suspended materials and pigments. In contrast, nitrate/nitrite concentrations were lower in effluent than in influent waters. These data provide a basis for analyzing the environmental impacts of warm-water aquaculture effluent discharges.     

Waste treatment in recirculating aquaculture systems

Recirculating aquaculture systems (RAS) are operated as outdoor or indoor systems. Due to the intensive mode of fish production in many of these systems, waste treatment within the recirculating loop as well as in the effluents of these systems is of primary concern. In outdoor RAS, such treatment is often achieved within the recirculating loop. In these systems, extractive organisms, such as phototrophic organisms and detritivores, are cultured in relatively large treatment compartments whereby a considerable part of the waste produced by the primary organisms is converted in biomass. In indoor systems, capture of solid waste and conversion of ammonia to nitrate by nitrification are usually the main treatment steps within the recirculating loop. Waste reduction (as opposed to capture and conversion) is accomplished in some freshwater and marine indoor RAS by incorporation of denitrification and sludge digestion. In many RAS, whether operated as indoor or outdoor systems, effluent is treated before final discharge. Such effluent treatment may comprise devices for sludge thickening, sludge digestion as well as those for inorganic phosphate and nitrogen removal. Whereas waste disposed from freshwater RAS may be treated in regional waste treatment facilities or may be used for agricultural purposes in the form of fertilizer or compost, treatment options for waste disposed from marine RAS are more limited. In the present review, estimations of waste production as well as methods for waste reduction in the recirculating loop and effluents of freshwater and marine RAS are presented. Emphasis is placed on those processes leading to waste reduction rather than those used for waste capture and conversion.     

Effect of organic fertilizer on heterotrophs and autotrophs: implications for water quality management

Alfalfa meal as a source of organic fertilizer was used in a series of pond, enclosure and laboratory experiments to determine its effect on bacteria, algae and water quality. Bacteria and flagellate algae were increased, whereas nonflagellate algae were not significantly affected by organic loadings. Bacterial and algal turnover rates we re 1.9-2.7 times daily and 0.18-0.22 times daily at 20-25^oC, respectively. Oxygen consumption rates were enhanced by increasing organic input or temperature. Dissolved oxygen in ponds with organic fertilizer was significantly lower than that in ponds without organic input. Because of low N and P content and high oxygen consumption, organic fertilizer alone is unlikely to provide adequate nutrients for algae and sufficient oxygen for fish. To stimulate the growth of food organisms for fish in aquaculture ponds, a combined use of inorganic and organic fertilizer is recommended, but the amount of organic fertilizer should be determined with care to avoid water quality deterioration. The amount of 10mg alfalfa 1^?1 wk^?1 is considered the upper safety limit for organic fertilization. The nitrogen and phosphorus ratio should be kept weekly at 20:1 by weight to promote the development of food organisms in ponds.     

Effects of shrimp pond water on phytoplankton: importance of salinity and trophic status of the receiving environment

Aquaculture generates a large load of effluents rich in organic matter and nutrients that may be introduced into the environment. This study aimed to assess in a microcosm experiment, the effect of shrimp pond water mixed with Patos Lagoon estuary water on phytoplankton chlorophyll a and primary production, simulating two salinities. Chlorophyll a, dissolved inorganic nutrients and primary production were measured in two experiments. In Harvest I, salinity of shrimp pond and environment water was similar, and chlorophyll a showed different trends over time, according to the amount of nitrogen available. In Harvest II, with different salinities and high nutrient concentrations in environment water, chlorophyll a levels showed a similar increasing trend over time in all mixtures. Net primary production showed differences among treatments in the first sampling in Harvest I, but not in the second, whereas no differences were observed among treatments in Harvest II. We conclude that shrimp pond effluent can lead to short‐term variations in chlorophyll a and primary production levels, with similar salinities. Salinity differences result in lower chlorophyll a and primary production values than expected according to the nutrient input. Differences in salinity can be an important management strategy to choose the best harvest period.     

Water temperature,time of exposure and population density are key parameters in Enteromyxum leei fish-to-fish experimental transmission

Enteromyxum leei is a myxozoan histozoic parasite that infects the intestine of several teleost fish species. In gilthead sea bream (Sparus aurata), it provokes a chronic disease, entailing anorexia, delayed growth, reduced marketability and mortality. Direct fish-to-fish transmission, relevant in aquaculture conditions, has been demonstrated for E. leei via effluent, cohabitation, and oral and anal routes. However, the minimum time of exposure for infection has not been established, nor the possible effect on the fish immune response. Two effluent trials were performed at different temperatures (high: average of 25.6°C; and low: constant at 18°C), different times of exposure to the effluent (1, 3, 5 and 7 weeks) and different population densities. The results showed that 1 week was enough to infect 100% of fish at high temperature and 58.3% at low temperature. High temperature not only increased the prevalence of infection in posterior intestine, but also induced a higher production of specific antibodies, limiting the progression of the infection along the intestine. Longer time of exposure to the parasite and higher fish densities facilitated E. leei infection. These results show that effective diagnosis, lowering animal density and removal of infected fish are key aspects to manage this disease in aquaculture facilities.     

The role of aquaculture in the sustainable development of irrigated farming systems in Punjab, Pakistan

Natural resource managers in Pakistan today preside over a massive investment in water distribution infrastructure. An historical bias towards large-scale irrigation systems and a focus on water use for arable crop production appears to have contributed to an imbalance in food production in the region. This has resulted in the diminished supply and elevated price of fish and meat products, compounded by the disruption of natural fisheries. The situation is inconsistent with the regions food security needs and an important potential role exists for increased aquaculture development. Physically and organizationally, the integration of various fish production approaches into existing land and water use practices would also appear to be fundamentally feasible. There would appear to be strong economic justification for diversified water use involving fish production, especially small and medium-scale carp production in ponds, using ground water. More broadly, within the context of the limited potential for further expansion of water resources, integrated aquaculture could contribute a vital productive element to various components of the water distribution arid irrigated farming systems in the Punjab. These include: supply canals, provided diverse institutional and engineering objectives can be accommodated; groundwater (including potential application of saline groundwater); the farm sub-system, especially integrated rice and fish production options in conjunction with alternative pest control strategies such as Integrated Pest Management; and irrigation drainage systems, where water quality permits. Therefore urgent broad research objectives should include the definition, investigation and development of a series of distinct economic and environmentally sustainable approaches to integrated animal protein production from aquatic resources, presently managed principally for agricultural production. Approaches should involve both the replacement of lost fishery potential resulting from large-scale irrigation development and flood control management, and the development of net gains in aquatic output, and should focus particularly on efforts to promote recycling of agricultural residues, reduced pesticide use and efforts to make better use of scarce water resources through the integrated aquaculture production across a broad range of water resources. An increasing number of countries are approaching full development of their surface water resources, and like Pakistan many face the development of new management approaches to increase diversity and improve productivity in relation to water use. The lack of research in support of the development of integrated aquaculture, which lags many years behind comparable agricultural research, may be constraining the breadth of choice available to natural resource managers to meet their food security needs.     

Rates of fish waste production and effluent discharge from a recirculating system (biofish) under commercial conditions

Application of the regulatory principle of ‘best available technology’ (BAT) to fish farm effluent control has, to some extent, been a driving force for the development of new culture and treatment technology. In Norway today, there are a number of farms for the production of Atlantic salmon, Salmo salar L., smolts and brown trout, Salmo trutta L., fingerlings that utilize microstrainers for the removal of particles from the effluent water. At least one commercial farm also utilizes a simplified recirculation system called BIOFISH as a demonstration of new and alternative technology for the production of brown trout restocking fish. In this paper, calculated effluent discharge and rates of waste production from the biofish demostration trials are compared to literature data and to measurements on un-treated as well as microstrained effluents from the production of Atlantic salmon smolts in a traditional flow-through tank system. Rates of fish waste production in the biofish trials were obtained from mass-balance calculations based on measured concentrations of water quality parameters at several points in the system. The results of these calculations show fish waste production rates that are low, but comparable to data found in the literature. Given the level of waste treatment that takes place in the biofish tanks, the specific effluent discharge levels from those tanks, in terms of grams per kilogram biomass and grams per kilogram feed, are considerably lower than those found for salmon smolt production in traditional flow-through tanks. There are also substantial differences in hydraulic self-cleaning properties of the two systems and a corresponding difference in the distribution of effluent discharge during normal tank operation and during tank/effluent pipeline flushing. The results presented here give valuable information related to: (1) waste output characterization; (2) the long-term efficiency of commercially available particle separation systems; and (3) the capabilities of the simplified biofish recirculation technology under field conditions.     

A variable growth rate modification of von Bertalanffy's equation for aquaculture

Abstract. In aquaculture experiments of only a few months'duration, fish can approach their asymptotic size and growth rates may change greatly. One objective of aquaculture is to obtain a maximum economic return, and a growth model is needed to relate rate of growth to food consumption and other costs to find the optimum duration of growth cycles. Von Bertalanffy's equation is an asymptotic growth model which can be used for this purpose. A variable growth rate model was developed to describe fish growth oscillations observed in aquaculture experiments. This growth model provides improved estimates of von Bertalanffy's equation in aquaculture and can be used for an efficient evaluation of fish production during production cycles.     

基于有机水产养殖对农业面源污染的比较研究

我国农业面源污染的核心问题是水体的氮、磷富集,目前尚无有效的工程治理方法,本研究通过有机水产养殖减轻水体的氮、磷污染。结果表明,有机水产养殖可以有效降低养殖水体的COD、无机氮和无机磷的浓度,有机海水养殖控制污染物排放的效果较有机淡水养殖更明显;有机养殖方式下严格而系统的管理措施及饵料质量的控制可能是减少氮、磷富集的主要因素。     

Environmental Conditions and Channel Catfish Ictalurus punctatus Production under Similar Pond Management Regimes in Alabama and Mississippi

This study was conducted to compare water quality and channel catfish production in earthen ponds located in two dissimilar physiographic regions of the southeastern United States and supplied with water of disparate quality. Ponds at Auburn, Alabama are on acidic Piedmont soils and filled with poorly mineralized runoff water; ponds at Stoneville, Mississippi are on slightly alkaline alluvial clays and filled with groundwater of high total alkalinity and hardness. Channel catfish were stocked at 8,750 fish/ha, fed daily, and provided nightly aeration in 0.04-ha ponds at both sites. Ponds were managed as similarly as possible. Minimum daily water temperatures and pH were higher at Stoneville than at Auburn, and there were greater concentrations of suspended clay turbidity, dissolved inorganic phosphorus, total ammonia-nitrogen, and nitrite-nitrogen at Auburn than at Stoneville. The taxonomic composition of the phytoplankton community was broadly different between the two sites. Taste tests revealed off-flavor in fish at both sites, but there were no significant differences (P > 0.05) in flavor scores between sites. The quality of flavor was somewhat different between sites, and these differences in quality were thought to result from observed differences in the taxonomic composition of phytoplankton communities. All differences in water quality seemed to be directly or indirectly related to the dissimilarity in the quality of the water supply and soils at the two locations. Although some water quality variables differed between sites and changed over time at both sites, environmental conditions never deteriorated enough at either site to cause serious stress or mortality in fish. There were no significant differences (P > 0.05) in average net fish production, survival, weight of individual fish at harvest, or feed conversion ratios. Average net fish production and feed conversion ratios, respectively, were 4,905 kg/ha and 1.27 at Auburn and 5,286 kg/ha and 1.27 at Stoneville. The results of this study demonstrate the need for site-specific investigations when conducting certain types of aquaculture research.     

Review of trends in the development of European inland aquaculture linkages with fisheries

Aquaculture is a multifaceted, dynamic food production sector in Europe. The average annual growth rate of aquaculture production in Western Europe was 5.5% between 1988 and 1998, while in Eastern Europe production declined by 56% during the same period. The main growth in aquaculture production has taken place in the marine environment, particularly in the expanding salmon, Salmo salar L., industry of Northern Europe. Inland aquaculture only contributed 19% of the total aquaculture production in 1998. Trout in Western Europe, and common carp, Cyprinus carpio L., in Eastern Europe are the dominant species in inland aquaculture. Inland fisheries production has been stagnant in Western Europe and has declined considerably in Eastern Europe. The importance of recreational fisheries is increasing all over Europe, although no reliable data are available on angler catches. The major interactions between aquaculture and fisheries are pollution by untreated effluents from farms and impacts on indigenous fish stocks. The conflict is decreasing as more advanced systems are used in inland aquaculture, including water recirculation and effluent treatment. The positive benefit of aquaculture is that the sector supports extensive stocking programmes in commercial and recreational fisheries all over Europe.     

Review of Aquaculture Research and Development of the Australian Freshwater Fish Silver Perch,Bidyanus bidyanus

Silver perch, Bidyanus bidyanus (Mitchell), is a freshwater fish that is endemic to the Murray‐Darling River System, Australia. Over recent decades, its distribution and abundance in the wild have declined, and it is now a threatened species with the conservation status of “vulnerable.” Silver perch is a schooling, omnivorous fish, with white flesh, few bones, and high levels of omega fatty acids, and its aquaculture potential has long been recognized. Hatchery techniques, based on hormone‐induced spawning of captive broodfish in tanks and rearing of larvae in fertilized earthen ponds, were developed in the early 1980s. Fingerlings are currently used for stock enhancement and conservation or sold for commercial grow‐out or stocking farm dams. Research into the grow‐out of silver perch commenced in 1990 and demonstrated that it is an excellent fish for culture in static aerated earthen ponds with high survival rates (>90%), fast growth rates (2–5 g/fish/d) at high stocking densities (20,000/ha) leading to high production rates (10 tonnes/ha/yr). Since 1996, there has been research into nutrition, diet development, feeding strategies, broodfish domestication and management, culture in tanks and tank‐based recirculating aquaculture systems, diseases, health management, genetic improvement, and cage culture. Silver perch is a hardy species that performs well under different culture conditions and on diets with no or low levels of fish meal. Technology has been transferred to industry through major conferences in 1994 and 2003 as well as workshops, field days, extension, seminars, and numerous scientific and technical publications. The high quality of silver perch and its excellent culture attributes suggest that the species has the potential to form a large industry based on high‐volume, low‐cost production. However, despite these features and a strong technical base provided by research and development, industry growth has been limited and a relatively small industry currently produces only around 500 tonnes annually. Development has been restricted by a number of factors: poor site selection and design of some farms; use of inappropriate husbandry and/or production strategies; difficulties with pond production, including significant losses to bird predation and diseases; high costs of feeds; limited marketing and promotion; no processing component; no large‐scale investment; and the failure of many farms that were too small to be economically viable. Recent research has found that silver perch performs well in cages (high survival [>90%], good growth [1.7–3.5 g/fish/d], and high production rates [50–90 kg/m³]), and cage culture has advantages such as ease of management and prevention of bird predation that may help overcome some of the problems associated with pond production. Improved health management, new production strategies, cage culture, use of interstrain hybrids and other genetically improved fish, and integration with cotton and other irrigation industries offer opportunities for increased production and efficiencies, and further development of the silver perch industry. The potential of silver perch for commercial aquaculture remains very high.     

Utilization of the filter feeder polychaete Sabella

The filter feeder sabellid Sabella spallanzanii Gmelin (Polychaeta, Sabellidae) was proposed as biofilter in the treatment of wastes from intensive aquaculture. The species was previously studied concerning reproductive traits and ecological requirements; moreover, previous laboratory experiments indicated a positive action of its feeding activity on solid removal from water column coupled with an interesting microbiological activity. In the present paper data on settlement and growth rate from a natural population, together with data on the bioremediation activity of an adult population, relative to an experiment conducted in a small fish farm are reported. Results seem to encourage further studies on S. spallanzanii for a future utilization in bioremediation of fish farms with recycled water. Data from natural annual settlement indicated, however, the unreliability in obtaining settlers from natural populations, so that the artificial reproduction of the target species will be one of the main points of further investigations.