Fertilization efficiency of cryopreserved sperm from striped catfish, Pangasius hypophthalmus (Sauvage)

The fertilization efficiency of cryopreserved sperm was compared with fresh sperm from striped catfish, Pangasius hypophthalmus . Of the two sets of experiments carried out, the first compared four sperm doses using fresh sperm and fresh eggs. The second experiment compared six concentrations of cryopreserved sperm ranging from 6.94 × 10⁷ to 6.94 × 10¹⁰ to fertilize 100 eggs per batch. Fertilization, hatch and survival rates were compared between cryopreserved and fresh sperm. The highest fertilization rate (53.75±1.62%) was achieved with a sperm dose of 6.94 × 10⁸. Increasing the sperm dose to 3.47 × 10⁹ did not increase the fertilization rate, indicating that the optimum sperm:egg ratio lies between 6.94 × 10⁶ and 3.47 × 10⁷ sperm per egg. Both highest (6.94 × 10¹⁰) and the lowest (6.94 × 10⁷) sperm doses resulted in lower fertilization rates (2.04% and 16.90% respectively). No significant differences were found among four fresh sperm doses compared. Mean hatch and survival rates resulting from fresh and cryopreserved sperm were similar. The experiment shows that while only 1.89 × 10⁶ fresh spermatozoa was required to fertilize a fresh egg, 6.94 × 10⁶ (or 3.67 times more) cryopreserved sperm was required to achieve the same level of fertilization. This provides important information for making decision to cryopreserve sperm for commercial and/or conservation purposes.     

Cryopreservation of YamúBrycon siebenthalae Milt

The yamú Brycon siebenthalae is an endemic fish of the Orinoco river basin, but wild stocks are decreasing because of the disruption of their habitat. We evaluated a protocol for the cryopreservation of yamú sperm to contribute to the preservation of this endangered genetic resource. Milt was mixed with a cryoprotectant medium (5.5% glucose, 12% egg yolk, and 5%, 10%, or 15% dimethyl sulfoxide - DMSO) in a ratio 1:4 (milt:medium), stored in 0.5-mL French straws, frozen in nitrogen liquid vapor (-76 C), then immersed and stored in liquid nitrogen for 10 d or 12 mo. Motility of thawed spermatozoa was higher ( P < 0.001) in 10% DMSO medium than 5% DMSO or 15% DMSO mediums; but lower than the control ( P < 0.001). With sperm cryopreserved, the highest level of fertilization was achieved with 10% DMSO ( P < 0.001) after 10 d or 12 mo of cryopreservation. Fertilization of eggs inseminated with 6.4 × 10⁹ spermatozoa per g of eggs was higher ( P <0.05) than with 1.6 × 10⁹ spermatozoa per g of eggs. There was no difference (P > 0.05) in fertilization between insemination doses of 3.2 × 10⁹ and 6.4 × 10⁹ spermatozoa per g of eggs. Cryopreservation of yamu milt can be performed successfully with a simple medium combined with 10% of DMSO as cryoprotectant. The highest level of fertility was achieved using between 3 × 10⁹ and 6 × 10⁹ spermatozoa per g of fresh eggs.     

Vaccination of Mixed and Full-Sib Families of Channel Catfish Ictalurus punctatus Against Enteric Septicemia of Catfish With a Live Attenuated Edwardsiella ictaluri Isolate (RE-33)

These studies were conducted to evaluate the efficacy of a live attenuated Edwardsiella ictaluri vaccine against enteric septicemia of catfish. In one study channel catfish fingerlings (72 d of age post hatch) were immersed for 30 min in water containing E. ictaluri RE-33 at dosages of 1 × 10⁶, 1 × 10⁷ and 2 × 10⁷ CFU/ML of water. No mortalities were observed following vaccination. Following exposure to virulent Edwardsiella ictaluri the cumulative mortality of fish vaccinated with dosages of at least 1 × 10⁷ CFU/mL were significantly lower than that of non-vacccinated fish in both laboratory and field challenges. Vaccination with 1 × 10⁶ CFU RE-33mL provided some protection during the laboratory challenge but failed to protect fish under field conditions. In a second study, vaccination of 6 full-sib families of channel catfish at a vaccine dosage of 1 × 10⁷ CFU/mL resulted in a relative percent survival among families ranging from 67.1 to 100%. Significant differences in mortality were found among families and between vaccinated and unvaccinated groups, but there was no family by vaccine interaction. Families with the highest mortality after vaccination were also shown to have the highest mortality without vaccination (r = 0.82; P = 0.04).     

Comparative sensitivity of carp, Cyprinus carpio L. and rainbow trout, Salmo gairdneri Richardson, to Renibacterium salmoninarum

Abstract. The pathogenicity of Renibacterium salmoninarum to carp, Cyprinus carpio L., and rainbow trout, Salmo gairdneri Richardson, was investigated. All carp injected with 4·8 × 10⁸ cells/fish, or 4·8 × 10⁷ cells/fish survived for 38 days. R. salmoninarum was isolated from all moribund fish, but not from the kidney of surviving fish, although R. salmoninarum antigen was detected in several of these fish by the dot blot assay. On the other hand, mortality in rainbow trout was 95% in the fish injected with 4·8 × 10⁸ cells/fish, and 15% in those which received 4·8 × 10⁷ cells/fish. R. salmoninarum antigen was detected by the dot blot assay in all surviving rainbow trout. The number of R. salmoninarum cells was immediately decreased by carp or rainbow trout serum, and the serum bactericidal activity of carp was higher than that of rainbow trout. Carp blood leucocytes had higher phagocytic activity than those of rainbow trout.     

The susceptibility of salmonid fish to an atypical strain of Aeromonas salmonicida that infects goldfish, Carassius auratus (L.), in Australia

Abstract. An enzootic, Australian, atypical strain of Aeromonas salmonicida isolated from diseased goldfish, Carassius auratus (L.), was inoculated into Atlantic salmon, Salmo salar L., brown trout, S. trutta L., rainbow trout, S. gairdneri Richardson, and brook trout, Salvelinus fontinalis (Mitchill), fingerlings by intraperitoneal injection (i.p.) and by bath challenge, the latter with and without prior abrasion of skin. The 10-day LD₅₀ (i.p.) was estimated to be 7·4 × 10^-3 colony forming units (cfu) for Atlantic salmon, 3·0 × 10^-2 cfu for brown trout, 3·7 × 10² cfu for brook trout and 6·4 × 10³ cfu for rainbow trout. Brown, rainbow and brook trout succumbed to bath challenges with between 10⁵–10⁶ cfu/ml, developing ulcers of the skin and septicaemia. The organism was trasmitted from inoculated fish to five of 195 within-tank control fish via water and established a carrier state in one of 14 Atlantic salmon. It was concluded that the organism poses a significant threat to the salmonid farming industry and wild salmonid fisheries in Australia.     

Temporal variation of seasonality of egg production and the spawning biomass of Pacific anchovy, Engraulis japonicus, in the southern waters of Korea in 1983–1994

Embryonic mortality, egg production and the spawning stock biomass of Pacific anchovy, Engraulis japonicus , off Southern Korea during 1983–1994, and their biological response to oceanographic features in spring and summer, were analysed. The instantaneous mortality rate (IMR) of embryonic stages decreased in spring and increased in summer, with a range of 0.33–1.23 day^–1 in spring and 0.78–1.69 day^–1 in summer. Egg production in summer was three times that during spring and production was low in the late 1980s. Mean lengths of yolk-sac larvae and adult females were greater in spring than in summer, whereas spawning fraction and spawning stock ratio (spawning biomass:adult biomass) were lower in spring than summer. Estimated mean spawning stock biomass ranged from 141 × 10³ to 380 × 10³ MT in spring and from 221 × 10³ to 557 × 10³ MT in summer. Statistically, the seasonal and long-term trends of embryonic mortality, egg production and spawning stock biomass of Pacific anchovy can be explained largely by spring warming, summer cooling and by less abundant zooplankton in the late 1980s.     

Progress in Controlled Maturation and Spawning of Summer Flounder Paralichthys dentatus Broodstock

Abstract— Wild-caught, adult summer flounder Paralichthys dentatus (avg. wt. = 740 g; range = 264–1,540 g; N = 60), collected in northeastern US coastal waters during October 1994, were transported to Vero Beach, Florida in March 1995 and held in 2.6-m³ indoor tanks through November 1995 under two artificial photothermal regimes: (1) natural regime, simulating natural habitat conditions; and (2) accelerated thermal regime, with seasonal temperature changes advanced by one month. A third group of fish was held in outdoor tanks under ambient photothermal conditions. Under all photothermal conditions, onset of vitellogenesis was associated with declining daylength and temperature, beginning in the accelerated group, then progressing to the natural and the ambient groups. From 20 September to 28 November 1995, 23 vitellogenic stage females from the accelerated and natural regimes were implanted with a cholesterol-cellulose pellet containing LHRH-a (100 μg/kg body wt). Females with initial mean oocyte diameters ranging from 258–456 μm spawned voluntarily 2.5–5.5 d postimplantation, while no maturational response was obtained from females with mean diameters ranging from 165–231 μm. Two females were spawned twice during the study period by LHRH-a pellet implantation. Infrequent, natural spawning without hormone intervention was also obtained. Females released from 22.7–396.9 × 10³ eggs on the first day of spawning, with fertilization and hatching rates of 0–93.470 and 0–81.1%, respectively.     

Natural Spawning of Captive Bigeye Scad Selar crumenophthalmus in Hawaii

Abstract.— Juvenile bigeye scad Selar crumenophthalmus were caught from the wild by hook and line and reared over 3 yr to establish a spawning broodstock of this species. The size at first maturity for captive males and females was 19-cm and 25-cm fork length (FL). Natural spawning of captive individuals occurred during the first year in captivity. The broodstock were observed to spawn repeatedly throughout their second and third years in culture. This species is a multiple spawner producing approximately 96 × 10³ to 121 × 10³ eggs/spawning group, 5 to 10 times per year. Stocking densities of 1–8 individuals/m³ were found to be suitable for natural spawning to occur. Collectively, the results indicate that this species exhibits notable potential for artificial propagation.     

Variation in fish community composition along an Iberian river basin from low to high discharge: relative contributions of environmental and temporal variables

Abstract – Factors associated with the spatial and temporal variation of the lower Guadiana basin (southern Iberia) fish community were determined using data from 20 sites sampled during the summer of 1994 (dry year following a period of low discharge, total discharge from 1992 to 1994=1.45×10⁹ m³) and again during the summer of 1996 (wet year following a period of higher discharge, total discharge from January 1995 to August 1996=6.18×10⁹ m³). From the 17 explanatory variables initially considered six were retained for analysis by a forward selection procedure: maximum depth, altitude, channel width, substrate coarseness, SALT (a dummy variable identifying sampling locations belonging to tributaries that discharge to the brackish Guadiana) and YEAR (a dummy variable identifying the sampling year). Further, we partitioned the total variability in the Guadiana fish community into that accounted uniquely by selected environmental variables (34.9%), uniquely by sampling year (4.1%), by both sampling year and environmental variables (0.3%), and unexplained (60.7%). ^NOTE     

Effects of temperature, salinity and irradiance on the growth of the toxic dinoflagellate Gymnodinium catenatum (Dinophyceae) isolated from Hiroshima Bay, Japan

ABSTRACT: Temperature and salinity ranges in which Gymnodinium catenatum (Hiroshima Bay strain) showed specific growth rates higher than 0.2/day were approximately 20–30°C and 20–32. The specific growth rate (μ), expressed as a polynomial equation as functions of temperature ( T ; °C) and salinity ( S ) were μ = (−6.84 × 10⁻⁴ T ² + 0.0354 T – 0.213) × (−1.03 × 10⁻³ S ² + 0.0579 S – 0.548)/0.31; the maximum growth rate (0.31/day) was obtained at 25°C and 30. From a comparison with field data recording temperature, salinity and light intensity, this species may be expected to bloom from summer to autumn in Hiroshima Bay.     

Preliminary investigations on the effects of dietary lipid on the spawning performance and egg quality of black sea bass Centropristis striata L

Adult black sea bass Centropristis striata broodstock ( N =162) were fed three different dietary treatments: two commercially prepared diets with 45% protein and two different lipid levels (12% and 20%) (diets 1 and 2), and a diet of frozen Atlantic silversides Menidia menidia (SS, diet 3). Broodstock were held under controlled photothermal conditions and induced to spawn with an LHRHa pellet (72 μg kg⁻¹ bw). Dietary lipid had pronounced effects on spawning performance and egg quality. Diet 3 (SS) produced a significantly ( P <0.05) higher fertilization success (22.4%) than diets 1 (0.6%) and 2 (4.8%). The hatching success of fertilized eggs was similar in all diets (range=40–58.6%), but only two spawns from diet 1 (12% lipid) yielded viable yolk-sac larvae (YSL). Diet 3 (SS) also produced significantly more YSL per female (21.8 × 10³) than the diet 1 (0.3 × 10³). Eggs from diet 3 (SS) contained a significantly greater proportion of n-3 series fatty acids, with docosahexaenoic acid (DHA) as the largest fraction. Eggs from commercially prepared dietary treatments contained significantly more n-6 fatty acids. The poor spawning performance of fish fed diet 1 (12% lipid) may be related to higher levels of linoleic acid and lower levels of DHA in the diet.     

An experimental investigation on aspects of infectious salmon anaemia virus (ISAV) infection dynamics in seawater Atlantic salmon, Salmo salar L.

This study investigated infection dynamics of infectious salmon anaemia virus (ISAV) by conducting two experiments to examine minimum infective dose and viral shedding of ISAV. In terms of minimum infective dose, the high variability between replicate tanks and the relatively slow spread of infection through the population at 1 × 10¹ TCID₅₀ mL⁻¹ indicated this dose is approaching the minimum infective dose for ISAV in seawater salmon populations. A novel qPCR assay incorporating an influenza virus control standard with each seawater sample was developed that enabled the quantity of ISAV shed from infected populations to be estimated in values equivalent to viral titres. Viral shedding was first detected at 7 days post-challenge (5.8 × 10⁻² TCID₅₀ mL⁻¹ kg⁻¹) and rose to levels above the minimum infective dose (4.2 × 10¹ TCID₅₀ mL⁻¹ kg⁻¹) on day 11 post-challenge, 2 days before mortalities in ISAV inoculated fish started. These results clearly demonstrate that a large viral shedding event occurs before death. Viral titres peaked at 7.0 × 10¹ TCID₅₀ mL⁻¹ kg⁻¹ 15 days post-infection. These data provide important information relevant to the management of ISA.     

Importance of the Straits of Florida spawning ground to Atlantic sailfish (Istiophorus platypterus) and blue marlin (Makaira nigricans)

Much of the uncertainty in managing highly migratory pelagic species results from the scarcity of fisheries-independent data relevant to determining long-term trends in abundance, migratory movements, and the relative importance of different spawning grounds. To address these issues, we used an ichthyoplankton-based method to quantify the overall level of spawning of sailfish ( Istiophorus platypterus ) and blue marlin ( Makaira nigricans ) in the Straits of Florida (SF). We estimated that during the 2 years (2003–2004) of the study, 4.60 × 10¹¹ sailfish eggs and 4.49 × 10¹¹ blue marlin eggs were produced on an annual basis in this region. These egg production values, when combined with estimates of annual fecundity for each species and the most recent stock assessment estimate of total biomass, indicate that about 2.1% of Western Atlantic sailfish spawning and 1.6% of Atlantic-wide blue marlin spawning occurs in the SF. Additionally, pop-up satellite tags deployed on sailfish at the start of the spawning season revealed their short residency times in the SF, suggesting that a large (≈13%) transient portion of the sailfish population is responsible for the SF egg production. Overall, this study provides a critically needed fisheries-independent method of quantifying spatial and temporal trends in the abundance of highly migratory species. The application of this methodology in the SF indicated that above-average levels of sailfish and blue marlin spawning occur in this area and, possibly more importantly, that the SF is a migratory bottleneck for these species.     

Cultivation of Trypanosoma danilewskyi (Laveran & Mesnil, 1904) in serum-free medium and assessment of the course of infection in goldfish, Carassius auratus (L.)

Abstract. Purification and in vitro cultivation techniques were developed for the fish haemoflagellate, Trypanosoma danilewskyi. The parasites were isolated and purified from the peripheral blood of experimentally infected goldfish, using a combination of Ficolt-paque gradient centrifugation to remove fish red blood cells and in vitro incubation to remove the remaining fish leucocytes. A serum-free culture medium for T. danilewskyi supported both short- and long-term cultivation of the haemoflagellates. The serum-free medium is a mixture of reagents available commercially: Leibovitz's L-15 medium, Dulbecco's Modified Eagle Medium and Hank's balanced salt solution. The doubling time was calculated to be 44.4 × 7.8h. Typically, a two- to five-fold increase in the number of cultured parasites was observed on day 7 after subculture with 1 × 10⁶ and 5 × 10⁵ trypanosomes ml⁻¹, respectively. When administered to fish, the in vitro -derived parasites caused an infection and pathology whose characteristics were similar to those observed following infection with trypanosomes obtained from infected goldfish. The freshly isolated and in vitro -grown parasites were successfully cryoprescrvcd in the culture medium containing 10% glycerine at −80°C for at least 3 months. Although the viability of the parasite decreased by 40–50% after thawing, cryoprcserved parasites retained the ability to infect goldfish.
Correspondence: Dr M. Belosevic, Associate Professor, Department of Zoology, CW-312 Biological Sciences Building, University of Alberta, Edmonton, AB, Canada T6G 2E9.     

The infectivity by different routes of exposure and shedding rates of Aeromonas salmonicida subsp. salmonicida in Atlantic salmon, Salmo salar L., held in sea water

Abstract. The infectivity of the bacterial fish pathogen Aeromonas salmonicida subsp. salmonicida to Atlantic salmon, Salmo salar L., in sea water was investigated and found to be similar to that reported for fresh water. The minimal infective dose in short duration bath exposures (1–3 days) was 10⁴ colony-forming units (cfu) per ml, while prolonged exposure for three weeks, but not for 1 week, produced infection with 10² cfu/ml. Intragastric intubation of A. salmonicida established infection with doses of >10⁵ cfu. Release of bacteria from dead or morbid infected fish was monitored and found to be in the order of 10⁵–10⁸ cfu/fish/h. These results emphasize the importance of removing dead fish from farm sites.     

Effects of dry pellets containing astaxanthin and squid meal on the spawning performance of striped jack Pseudocaranx dentex

ABSTRACT: This study was conducted to investigate the effect of squid meal and astaxanthin in dry pellets on the spawning performance of striped jack. Two groups of 8-year-old fish with an average bodyweight of 3.5 ± 0.4 kg were used. The control group was fed a raw fish mix (RF) and the experimental group was fed steam dry pellets (as-DP) containing 10 p.p.m. astaxanthin and squid meal, the latter replacing half the fish meal. Each group was fed once a day, three times a week in floating net cages for a period of 5 months. Seven females and seven males were selected from each group and transferred to 65 m³ indoor concrete tanks for spawning, where they were kept at optimum spawning conditions (22°C) for 1 month. The average bodyweights of selected fish were 3.8 ± 0.5 kg and 3.8 ± 0.6 kg for the RF and as-DP groups, respectively. Both groups spawned a total of 18 times and the mean total egg production and egg quality, measured in terms of buoyancy, fertilization and hatching rates, showed no significant differences ( P > 0.05) between groups. Total larval production was 679.9 × 10³ and 678.1 × 10³ larvae/kg-female for the RF and as-DP groups, respectively. These results show that the combination of astaxanthin and squid meal in dry pellets for striped jack broodstock improved the overall spawning performance to a level similar to that of fish fed on RF.     

The life-history patterns of Barbus bocagei sclateri (Günther, 1868) in a tributary stream of the Guadalquivir River basin, southern Spain

Abstract– The age, growth and reproduction of Barbus bocagei sclateri (Günther, 1868) were studied from November 1987 to September 1989 in a tributary stream of the Guadalquivir River basin. The maximum ages observed were 8 + in males and 11 + in females. The seasonal growth began in April and lasted 4–6 months. The males matured during their third year of life (2 +) and females during their fifth/sixth year (4 +/5+). There was a significant difference in the overall sex ratio of 1. 3: 1 (961 males to 740 females). Reproductive activity started in April/May and lasted until June/July. The end of the reproduction period coincided with a fall in the percentage of oxygen saturation. During this reproductive period, females spawned 2 batches of eggs. The relationship between fecundity (Fec) and fork length (FL, mm) was: Fec= 7.54 × 10⁻⁴ FL^3.06 The maximum contribution to the fecundity of the population was observed in the 6 + female group. The reproductive effort was also maximum in this age. Compared with the rest of the European barbel populations studied, the life-history patterns of this stock are characterized by low annual growth, early maturity, reduced longevity and high fecundity.     

The Induction of Tetraploidy in Salmonids

The induction of tetraploidy was attempted in three intraspecies crosses (autotetraploid) of sal-monid: chinook salmon ( Oncorhynchus tshawytscha ), coho salmon ( O. kisutch ) and rainbow trout ( Salmo gairdneri ), and in the interspecies hybrid (allotetraploid) coho × Atlantic salmon ( Salmo salar ).
Pressure treatments of 6.2 × 10⁴ kPa (9,000 psi) were applied for six minutes at intervals from 50% of the time to cleavage to beyond first cleavage. Analysis of eyed stage embryos via flow cytometry indicated two periods of tetraploid induction existed corresponding to 55–75% and 100–110% of the first cleavage interval (FCI).
The effects of different pressures and the times of application were analyzed in a study with rainbow trout. Treatments of 4.8 × 10⁴ kPa (7,000 psi) for eight minutes, and 5.5 and 6.2 × 10⁴ kPa (8,000 and 9,000 psi) for four minutes, were applied at 65, 78, and 100% FCI. Tetraploids were found in the 5.5 and 6.2 × 10⁴ kPa group treatments only when applied at 65% FCI.
The results indicate that, while tetraploidy is inducible in salmonids, further experimentation is necessary to discern the appropriate time and treatment for optimal tetraploid induction in each species.     

Herpesviral haematopoietic necrosis virus (CyHV-2) infection: case studies from commercial goldfish farms

Herpesviral haematopoietic necrosis is a disease of goldfish, Carassius auratus , caused by Cyprinid herpesvirus-2 (CyHV-2) infection. Quantitative PCR was carried out on tissue homogenates from healthy goldfish fingerlings, broodfish, eggs and fry directly sampled from commercial farms, from moribund fish submitted to our laboratory for disease diagnosis, and on naturally-infected CyHV-2 carriers subjected to experimental stress treatments. Healthy fish from 14 of 18 farms were positive with copy numbers ranging from tens to 10⁷ copies μg⁻¹ DNA extracted from infected fish. Of 118 pools of broodfish tested, 42 were positive. The CyHV-2 was detected in one lot of fry produced from disinfected eggs. Testing of moribund goldfish, in which we could not detect any other pathogens, produced 12 of 30 cases with 10⁶–10⁸ copies of CyHV-2 μg⁻¹ DNA extracted. Subjecting healthy CyHV-2 carriers to cold shock (22–10 °C) but not heat, ammonia or high pH, increased viral copy numbers from mean copy number (±SE) of 7.3 ± 11 to 394 ± 55 μg⁻¹ DNA extracted after 24 h. CyHV-2 is widespread on commercial goldfish farms and outbreaks apparently occur when healthy carriers are subjected to a sharp temperature drop followed by holding at the permissive temperature for the disease.     

Continuous exposure to infectious pancreatic necrosis virus during early life stages of rainbow trout, Oncorhynchus mykiss (Walbaum)

Rainbow trout, Oncorhynchus mykiss (Walbaum), were exposed continuously to infectious pancreatic necrosis virus (IPNV) at 0, 10¹, 10³ or 10⁵ plaque forming units (pfu) L⁻¹ of water to estimate the effects of chronic IPNV exposure on early life stages. Fish density averaged 35 fish L⁻¹ (low density) or 140 fish L⁻¹ (high density), and the tank flow rate was 250 mL⁻¹ min. Virus exposure began at 6 days before hatch and continued until fish were 44 days old. Cumulative per cent mortality, analysis of survival and hazard functions, and discrete-time event analysis were used to explore the patterns of survival and mortality. In eggs and fish exposed to IPNV, mortality significantly greater than in the 0 pfu L⁻¹ exposure did not occur until IPNV concentration was 10⁵ pfu L⁻¹ at low fish density and 10³ pfu IPNV L⁻¹ at high fish density. These results suggest that in the natural aquatic environment, where rainbow trout densities are likely to be considerably lower than in this study, mortality resulting from infection with IPNV will very likely not occur when ambient concentrations of virus are ≤10³ pfu IPNV L⁻¹. In aquaculture rearing units, trout density is likely to be as high or higher than the densities used in this study. Therefore, continuous inputs of virus at concentrations greater than 10¹ pfu L⁻¹ may result in IPN epidemics in aquaculture facilities.