Wading Bird Depredations on Channel Catfish Ictalurus punctatus in Northwest Mississippi

We interviewed farm managers about their perceptions of wading bird problems and conducted preliminary surveys of wading bird populations at 67 randomly selected channel catfish Ictalurus punctatus pond complexes in northwest Mississippi during December 1995. At a subsample of 24 complexes and 10 other complexes previously surveyed in 1990, we surveyed wading bird populations bimonthly throughout the year in 1996 and observed great blue herons Ardea herodias and great egrets Ardea alba feeding at catfish ponds. Seventy-five percent of farm managers questioned felt that wading birds were causing losses to their fish stocks, and 74% believed the problem was increasing. Consistent with interview results, 88% of the pond complexes surveyed had one or more wading birds present. Despite reported harassment programs by producers, great blue heron densities at 10 complexes previously surveyed in 1990 had increased by more than eightfold in 1996. Great blue heron densities varied with location, season and time of day, but the average 127-ha farm supported about 78 herons and 56 great egrets. Despite similar populations, the potential impact of these two species was quite different. Live catfish, averaging 10.3 cm in length (circa 10 g) comprised only 8% of the egret diet by weight, and most of the fish were obtained from fingerling ponds during periods when these fingerlings may be weakened by the bacterial disease, enteric septicemia of catfish. In contrast, live catfish, averaging 16 cm in length (circa 34 g), comprised 44% of the great blue heron diet by weight. Herons foraged from both fingerling and food fish ponds, primarily in the early morning and evening. Based on average population densities and foraging rates, herons at the average 127-ha farm in northwest Mississippi consumed 114,000 (circa 3,900 kg) catfish, annually. However, further studies are recommended to document production losses.     

Evaluation of a Methyl Anthranilate-Based Bird Repellent: Toxicity to Channel Catfish Ictalurus punctatus and Effect on Great Blue Heron Ardea herodias Feeding Behavior

Abstract— We evaluated the methyl anthranilate-based bird repellent, ReJeX-iT TP-40™ (TP-40), for 1) its toxicity to channel catfish fingerlings (catfish), Ictalurus punctatus; 2) its effect on great blue heron (heron), Ardea herodias feeding behavior; 3) its efficacy in reducing heron predation on catfish; and 4) its effects on catfish growth. TP-40 effectively maintained MA concentrations near the water's surface and below toxic levels for catfish in the water column. Water samples collected from 0.03 and 0.35 m below the surface of catfish rearing tanks (6,664 L) treated at application rates up to the equivalent of 200 kg/ha contained less than 5 ppm active ingredient, which is less than the no observable effect limit for catfish fry. No treatment-related mortality of catfish was observed. Handling times of catfish fingerlings captured by herons from tubs treated with TP-40 initially increased at application rates of 19.6 kgha or greater but decreased as a function of the number of catfish captured. Under simulated aquaculture conditions, TP-40 did not affect the number of catfish eaten by herons from ponds treated at surface application rates of 0, 2, 22, and 220 kglha. TP-40 had no affect on the time herons spent handling live or dead catfish. Ponds treated with TP-40 at 220 kgha had a 46% increase in visibility (secchi disk method) and a 58% reduction in total suspended solids, suggesting the formulation was phytotoxic. TP-40 did not affect fish growth. Analysis of individual behavior showed that herons may have habituated or become indifferent to the effects of the repellent after repeated exposure. Under the conditions of the study, herons did not maintain their body weight unless catfish were made available by disease or supplemental feeding, suggesting that herons may be inefficient at capturing healthy catfish. Surface applications of TP-40 at 20 to 220 kg/ha were not effective in limiting predation by herons.     

Quantitative estimation of the predation of marine ranched striped jack <Emphasis Type="Italic">Pseudocaranx dentex</Emphasis> by herons

The Goto station of the Japan Sea-Farming Association conducted marine ranching experiments with striped jack Pseudocaranx dentex from 1988 to 1999 in the Goto Islands, Nagasaki, Japan. Marine ranching is a stocking method where released fish are fed for some period after release in order to decrease initial mortality from starvation. Ranched fish were fed for 0, 90, and 15 days after stocking in 1997, 1998, and 1999, respectively. During the experiment, herons (grey heron Ardea cinerea, black-crowned night heron Nycticorax nycticorax, and great egret Egretta alba) were often observed preying on released fish in the ranching area. The present study estimated the number of fish preyed upon by herons during observation periods in 1997, 1998, and 1999 from the number of herons that flew into the ranching area and the predation rate on ranched fish by herons. The former was counted during sightings. The latter was estimated from the sighting observations and heron regurgitations. The number of herons that flew into the ranching area increased with the feeding period. The numbers of fish lost to predation by herons in 1997, 1998, and 1999 were estimated to be 0, 5,741, and 829, respectively.     

Influence of improved feed quality and food conversion ratios on phosphorus loadings from cage culture of rainbow trout, Oncorhynchus rnykiss (Walbaum), in freshwater lakes

The expansion of freshwater cage culture in Scotland during the 1980s led to concern with respect to the impact of nutrient, particularly phosphorus (P), discharges on water quality in lakes. The primary route by which P enters the aquatic environment from cage farms is through the feed administered to the fish. In recent years, there have been considerable technological advances in feed manufacturing and improved feeding practices at farm level. This paper investigates how P inputs to freshwater lakes from cage farms may be reduced through changes in diets and improved food conversion ratios. The results demonstrate that there has been a significant improvement in the P content of freshwater trout diets in recent years and that it is possible to reduce waste P loadings from cage sites through the use of better-quality diets and improved feed management. In Scotland, production levels in freshwater cages are commonly set by the regulatory authority assuming a soluble waste P loading of 10 kg P tonne^?1 of fish produced. This study suggests that actual soluble waste P loadings are likely to be far lower than this and that, as a result, increases in water column total P levels may be overestimated.     

Transmission of some fish pathogenic viruses by the heron, Ardea cinerea

Abstract. Various possibilities of transmitting fish pathogenic VHS, SVC and IPN viruses by the heron, Ardea cinerea , were investigated. Shedding of IPN virus in the faeces could be demonstrated for a period of 7 days when about 1 g of IPN virus-infected trout fry was fed to the birds once only, whereas feeding larger quantities of infected fish on 5 consecutive days resulted in virus excretion for a further 5 days only. Infectious IPN virus could not be isolated from samples of blood and virus specific neutralizing antibodies could not be demonstrated in serum samples. A waterborne infection of trout fry was established by adding very small (0·2 g) quantities of faeces from herons fed IPN virus-contaminated fish to 20 1 water. Infectious SVC and VHS virus was also re-isolated from samples of food which were regurgitated by the herons at different times up to 120 min after feeding of contaminated fish. It was concluded that herons are able to act as mechanical vectors for IPN, VHS and SVC viruses and therefore, may be a potential source of infection and spread of the diseases.     

Salmonid Rearing in Floating Net Cages in Freshwater Reservoirs Owned by the Severn Trent Water Authority

The practical problems encountered by the Severn Trent Water Authority in setting up a cage rearing unit on a water supply reservoir are described. Rearing trials with rainbow trout and brown trout were undertaken over a two-year period. The results indicate that a higher stock density of fish per unit volume can be held in a cage than at an available fish farm. Feeding techniques and general management methods are discussed as food conversion ratios are approximately twice those at the fish farm, with growth and survival rates slightly lower. The capital and operating costs are considered to be less expensive than those for setting up a land based operation. A credit on total expenditure is recorded on a twenty year cash/flow analysis, with contrasted operating costs of £1,340 per tonne of rainbow trout produced at the cages and £1,562 at the fish farm.     

Solid waste production from rainbow trout, Salmo gairdneri Richardson, cage culture

Abstract. There is increasing concern over the environmental impact of freshwater cage culture, but there is a lack of information on the amounts and nature of the wastes produced. This study presents measurements of the total solid waste arid solid carbon, nitrogen and phosphorus loadings from five Scottish rainbow trout, Salmo gairdneri Richardson, cage farms, and shows a significant input of solids below the cages. The results indicate a considerable variability in solid output which was partly due to variations in the feeding rate of fish with the cages, but was also thought to be due to variations in management on individual farms. The results compare well with other studies on land-based pond and tank systems and provide useful estimates of solid waste loadings for the prediction of environmental impact.     

Acoustic conditioning for recall/recapture of escaped Atlantic salmon and rainbow trout

Escape of salmon from sea cages is a problem that continues to plague the aquaculture industry. Data collected during the past 15 years from Norway, Scotland, Ireland, Canada and U.S. suggest significant impacts on natural runs of fish and economic losses to producers. The present report investigated the feasibility of using acoustic conditioning as a means of recalling/recapturing escaped fish. Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) were found to respond to frequencies in the range of 50 - 400 Hz equally well. Subsequently, both species were conditioned to a 250 Hz acoustic tone during feeding. Juvenile and sub-adult fish readily conditioned to the acoustic signal within four days, with the maximum number of fish responding (85% salmon, 96% trout) by day seven. To assess retention of conditioning, fish were exposed to a single tone without feed reinforcement every one, two or four weeks. Salmon and trout continued to respond for a seven month period with no significant decrease (88% salmon, 97% trout) in response. No significant differences were observed in the response of either species to tones differing in frequency by up to 200 Hz (89% salmon, 96% trout) and intensity by 20 dB (91% salmon, 96% trout). Both species were reproducibly recalled to a cage or feeding ring in a 3.7 m tank, but were reluctant to re-enter the cage. The findings indicate that salmon and trout are readily conditioned to acoustic signals and retain that conditioning for an extended period of time without reinforcement. These characteristics suggest that acoustic conditioning has potential as a means to recall escaped salmon and when coupled with recapture, can reduce interactions with wild stocks and losses to the producer.     

A Comparison of the Performance of American Brook Trout (Salvelinus fontinalis Mitchell) and Rainbow Trout (Salmo gairdneri Richardson) Reared in Fish Farm Ponds and Freshwater Floating Net Cages

Following an upsurge in the interest to anglers of American brook trout (Salvelinus fontinalis) an investigation was carried out in 1978 and 1979 into their growth and survival when reared in fish farm earth ponds and freshwater floating cages. Their performance was compared with similarly reared batches of rainbow trout (Salmo gairdneri). This work shows that American brook trout require more care and attention than rainbow trout when reared artificially and that their survival to 1 year old is lower, although growth rate in the first year compares favourably.     

The effects of trout culture on diet and food availability of native freshwater fish populations

Cultivation of a species or population and distribution to various regions has raised the idea of negative impacts on native species. The effect of non‐native species on native species may be caused by competition for source, predation, hybridization, and parasite/disease transport. The present study aims to evaluate the possible effects of a trout farm established on the banks of Kocaba? Stream (Çanakkale, Turkey) on feeding characteristics of some freshwater fish (Phoxinus phoxinus, Barbus oligolepis, and Squalius cii). The samples were collected monthly over a year at two stations located before and after the trout farm and at a control station on the tributary not impacted by the effects of the farm. Fish and environmental samples were gathered monthly with an electroshocker and some fishing tools between August 2015 and July 2016. The fish diet and resource incorporation into biomass were evaluated by gut content and stable isotope analyses. Changes in diet preferences when the species are exposed to source stresses and some individuals fed on farm‐based feed contaminated from the farm in Kocaba? Stream. In this study, it was observed that native fish populations in aquaculture regions were influenced by diet preferences. Designing enclosed systems limiting feed and waste transit in aquaculture establishments may be suitable for sustainability of these species.     

Occurrence and prevalence of infectious pancreatic necrosis virus in rainbow trout (Oncorhynchus mykiss) cultured in cages in the Black Sea

Rainbow trout (Oncorhynchus mykiss) cultured in cage systems in the South Eastern Black Sea were surveyed for the type, occurrence and prevalence of infectious pancreatic necrosis virus (IPNV). Two nearby farms (designated as Farm A and Farm B) were visited monthly in 2007 and 2008. At each farm, 385 fish were selected randomly from five cages. Another farm with infected trout from a hatchery also was monitored for IPNV from the transfer to harvest. IPNV was found to be prevalent in both farms surveyed. In Farm A, IPNV was present throughout the growing period, from January to May, and all five randomly sampled cages tested positive for IPNV in March and April of 2007. In Farm B, IPNV was present only in February and March in 2007, and in 2008, IPNV was observed in January (two cages) and February (one cages) at low levels. Interestingly, IPNV was absent 2 weeks after transfer to the sea at 17.5°C. The same strain of IPNV, genotype III that was isolated from the same stock of fish at the hatchery, reoccurred when water temperatures dropped to 12°C in December in the Black Sea. Transferring fish to the sea at high water temperatures could lessen the negative impacts of IPNV on growth of rainbow trout in brackish water.     

Assessment of infectious salmon anaemia virus prevalence for different groups of farmed Atlantic salmon, Salmo salar L., in New Brunswick

Abstract Infectious salmon anaemia (ISA) virus (ISAV) has been causing disease in New Brunswick since 1996. As a control measure, all fish in an outbreak cage are killed. The objective of this study was to compare ISAV prevalence in cages experiencing an outbreak with healthy cages from the same farm, neighbouring farms and distant farms. Atlantic salmon from five different groups were tested using an RT-PCR test. Groups included moribund fish from a cage experiencing an outbreak (A), healthy fish from an outbreak cage (B), healthy fish from a negative cage from a farm experiencing an outbreak in a different cage (C), healthy fish from a negative farm near an outbreak farm (D), and healthy fish sampled at a negative farm located in an area with only negative farms (E). Apparent prevalences (standard error) for the different groups (A-E) were 0.94 (+/-0.026), 0.41 (+/-0.062), 0.29 (+/-0.040), 0.08 (+/-0.037) and 0.08 (+/-0.037), respectively. All groups were significantly different (P < 0.002) from each other except for groups B and C and groups D and E. Because the prevalence of the virus was significantly higher in the outbreak cage (B) compared with other sites, early harvest of outbreak cages will remove one source of virus. However, ISA negative cages (C) that remain on the positive farm may potentially act as a viral reservoir.     

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.     

Development,prospects and problems of the tilapia cage culture industry in The Philippines

The Philippines has vast freshwater resources for cage culture of fish. Two tilapia species, Tilapia mossambica and Tilapia nilotica, are cultured commercially in cages in several lakes.Field testing for cage culture of Tilapia nilotica, the preferred species, is described. A pilot commerical cage farm has been established.The major problems affecting development are the short supply of quality fingerlings, the lack of a standard commercial feed, and the increasing costs of cage construction. Recommendations for resolving these problems are given.     

Impact of Great Blue Heron Depredations on Channel Catfish Farms

With the growth of channel caffish Ictalurus punetatus production in the Delta Region of Mississippi over the last 30 years have come concurrent depredation problems caused by great blue herons Ardea herodias . Biomass in stomachs from herons collected at catfish farms averaged 41% catfish, 38% sunfish Lepomis sp ., 17% shad Dorosoma cepedianum , and 4% gambusia Gambusia sp.; whereas observations of herons foraging indicated that 45% of the prey taken were gambusia. Our observational data indicate that herons take an average of 12 10-cm catfish fingerlings daily. The diurnal density of foraging herons on catfish ponds averaged 0.17 herons/ha in 1990, which means that the average 127-ha farm supports approximately 22 herons. Nocturnal foraging, especially on dark nights, appears to be minimal. If our data are approximately correct, the average catfish farm could be losing $30/ha per yr to herons, assuming that this catfish fingerling mortality can be attributed solely to heron depredation.     

Effect of Stocking Density on Growth,Yield, and Costs of Producing Rainbow Trout,Oncorhynchus mykiss,in Cages

Abstract

Rainbow trout, Oncorhynchus mykiss, were raised in culture cages (1 m³) to determine the effect of stocking density on growth, survival, and percentage of market-size fish. Large fingerling rainbow trout (20-25 cm, 232 g average weight) were stocked into six cages located in a 0.4-ha pond. Two stocking densities (100 or 200 fish/cage) were used, and fish were grown for 140 days (2000-April 2001). Average total harvest weight (35.0 kg) in the low-density cages was approximately one-half the average total harvest weight (61.2 kg) in the high-density cages. Average weight gain (11.7 kg to 15.1 kg) and feed conversion (1.2 to 1.5) were also smaller for the low-density cages. Average survival was 96.7% for the low-density cages and 94.2% for the high-density cages, with the percentage of market-size fish (< 29 cm) averaging 50.3% and 52.0%, respectively. Production costs for the actual experiment and the revenues from fish sold at the end of the study were collected. An enterprise budget based on the experimental results for the two densities was developed to determine if a culture operation of this size would produce a net return. Production costs and revenues from the experiment resulted in a large negative return (-$3,124) and high breakeven price ($13.53/kg).     

Effects of sea cage salmon farming on sediment nitrification and dissimilatory nitrate reductions

Within a few months of the establishment of a sea cage salmon farm in the Marlborough Sounds, New Zealand, sediment physical and chemical characteristics reflected the extremely high sedimentation rate immediately underneath the fish cages. In the surface sediment, dry weight was reduced to about one-third, density was halved and the volatile solids content increased about seven-fold compared with nearby sediments. Similarly, the sediment pools of ammonium, organic N and total phosphorus were much higher underneath the cages than at farther removed sites. The total N/P ratios were the same (1.5) in the surface sediment underneath the cages and in the feed but markedly higher in the less affected areas. In situ nitrification and denitrification were not measurable in the immediate vicinity of the salmon farm. The potentials for nitrification and denitrification gradually increased from virtually nil underneath the fish cages to commonly observed rates about 30 m from the cages. The complete absence of denitrifying enzymes in the salmon farm sediment to a depth of 6 cm explained why nitrate diffusing from the water column into the sediment was not denitrified. Within 10 m of the fish cages the bulk of added ¹⁵N-nitrate was reduced to ¹⁵N-ammonium. The results demonstrate that nitrification/denitrification in the immediate vicinity of a sea cage fish farm is not a significant mechanism of N removal.     

Behaviour of rainbow trout, Salmo gairdneri Richardson, in marine cages

Abstract. Underwater television was used to observe the distribution and swimming behaviour of groups of farmed rainbow trout, Salmo gairdneri Richardson, in marine net cages. Undisturbed rainbow trout (mean total length 240 mm) aggregated near the surface, remaining motionless in slack water and formed polarized shoals at higher current velocities. Larger fish (mean total length 317 mm) occupied deeper parts of the cage and were more active during periods of slack water. The results are compared with previous work on farmed Atlantic salmon, Salmo salar L., and discussed in relation to the biology of wild rainbow trout and recent work on exercise, growth and condition in salmonids.     

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.     

A synopsis of smolt production in cages in a coastal freshwater lake in Norway

Abstract. Fish farming activities based on salmonid smolt production in cages were monitored in a coastal freshwater lake in western Norway. Yearly ongrowth in the fish farm increased from 350kg in 1979 to 15150kg in 1985, while maximum biomass of standing stock increased to nearly 14000kg in the same period. Maximum daily mortality observed was 0·37% of total stock in August 1983 due to an Ichthyobodo necator infection.
Except for 1983, between 61 and 73% of annual amount of feed was used in the second half of the year. Total feed amount used in 1979–85 was 77750kg. The phosphorous effluents decreased from 88 to 90% of the feed content to 80·4% in 1984–85.
A set of easily calculated parameters for judging management possibilities and success in cage farming is proposed: annual heat sum; mortality rate; growth rate; feed conversion; and phosphorous retention in fish.