Cage-reared Fish Research Articles

Parasite abundance distribution as a model of host-parasite relationships between monogeneans Gyrodactylus spp. and cage-reared rainbow trout Oncorhynchus mykiss.

Aggregation is a fundamental feature of parasite distribution in the host population, but the biological implications of the aggregation indices used to describe the relationships between the populations of parasites and hosts are not evident. It is speculated that the form of distribution in each case is predicated on the host's varying resistance to the infection, which is hard to control, making it difficult to adequately interpret the index values. This paper examines several cases from trout farms in Russian Karelia to explore the monogenean Gyrodactylus spp. infection in rainbow trout of varying ages. The genetic homogeneity of cage-reared fish and the direct life cycle of the helminths make the relationship between the species more lucid than in natural host-parasite systems. The results give no ground to speak of any specific patterns: as well as in the natural systems, the infection rates in trout vary widely, i.e., the helminth distribution has not become more uniform; the observed distributions in all cases are adequately approximated by the negative binomial model; the positive abundance-occupancy relationships (AORs) and abundance-variance relationships (AVRs) common for parasitic systems apply to the basic infection parameters. The form of the negative binomial distribution is shaped by two parameters-k and θ, the former being a metric of the infection variability, which depends on the host's individual resistance, and the latter representing the parasites' reproduction and establishment success rates. A rise in the parameter k indicates increased aggregation and a higher parameter θ points to a more uniform frequency distribution. These parameters can be used as a representative tool for monitoring the parasite communities in salmonid fishes, including in aquaculture.

The skin mucosal barrier of lumpfish (Cyclopterus lumpus L.) is weakened by exposure to potential aquaculture production-related stressors.

Various cleaner fish species, such as the lumpfish (Cyclopterus lumpus L.), are used in the sea cage production of Atlantic salmon (Salmo salar L.) as a control measure against the ectoparasitic salmon louse (Lepeophtheirus salmonis). Nonetheless, during severe lice infestation, alternative treatments are required to control parasitic burden. The aim of this study was to gain insight into how lumpfish skin responds to different chemicals used to treat parasites. The authors collected skin from lumpfish from both research facilities (tank-reared fish) and commercial production (cage-reared fish) and used operational welfare indicators, in vitro models, histology and transcriptomics to study how the skin responded to two anti-parasitic oxidative chemicals, hydrogen peroxide (H2 O2 ) and peracetic acid. Lumpfish sampled from the farm were classified as clinically healthy or weak based on their morbidity status, and fish from each category were used to gain insight into how the therapeutics affect the skin barrier. Differences between healthy and weakened (moribund) fish, and between treated fish from each of the two groups, were observed. Histological examination showed an overall reduced skin quality in fish characterized as moribund, including different grades of exposed bony plates. In vitro oxidant-treated lumpfish skin had reduced the migration capacity of keratocytes, a weakened epidermal barrier, and altered gene transcription, changes that are known predisposing factors to secondary infections. Skin from non-treated, healthy fish sampled from commercial farms exhibited similar features and attributes to oxidant-exposed tank-reared fish from a research facility, suggesting that apparently healthy cage-held lumpfish exhibited stress responses in the epidermal barrier. The results of the study outline the risks and consequences lumpfish can face if accidentally subjected to potential anti-parasitic oxidant treatments aimed at Atlantic salmon. It also strengthens the evidence behind the requirement that lumpfish should be removed from the cages before being potentially exposed to this type of treatment and outlines the potential risks of differing husbandry practices upon lumpfish health, welfare and resilience.

ON THE INFECTION OF WHITEFISH WITH PLEROCERCOIDS TRIAENOPHORUS NODULOSUS (PALLAS, 1781) IN THE NIZHNETULOMSKOE RESERVOIR (MURMANSK REGION)

The object of the study is the whitefish Coregonus lavaretus (Linnaeus, 1758), which inhabits the Nizhnetulomskoe Reservoir (NTV) in the Tuloma River catchment. Parasitological analysis of the whitefish sampled in the framework of annual ichthyological monitoring was carried out. In two fish specimens, many large cysts (up to 7.0 mm) containing plerocercoids of the parasite Triaenophorus nodulosus (Pallas, 1781) were found on the fish liver. In waters of the Murmansk Region, this was the first case of whitefish infestationwith this helminth species. The infection rate was 5.4 %. In recent years, the rainbow trout Oncorhynchus mykiss (Walbaum, 1792) has been farmed in the NTV waters. To cagereared fish, this cestode is a pathogenic and highly dangerous parasite. The paper considers the vulnerability of the reservoir’s ecosystem to the impact, and the manifestation of fish diseases of various etiologies in recent years. In particular, there are occurrences of a disease of unclear etiology, ulcerative skin necrosis, in anadromous Atlantic salmon migrants, as well as infestation of juvenile salmon with the monogenean Gyrodactylys salaris (Malmberg, 1957). In the light of the alarming epizootic situation and due to the finding of a helminth not typical in whitefish in the NTV, integrated ichthyological, parasitological and hydrobiological studies are needed. The aim of these studies is to determine the extent and dynamics of fish infestation with the cestode T. nodulosus, and to track the transmission of the infection along the food chain of aquatic organisms in the ongoing succession processes in the ecosystem.

Morphological characterisation and identification of four species of Cardicola Short, 1953 (Trematoda: Aporocotylidae) infecting the Atlantic bluefin tuna Thunnus thynnus (L.) in the Mediterranean Sea.

Blood flukes of the genus Cardicola Short, 1953 are considered the most potentially pathogenic parasites in bluefin tuna cultures. Morphological study and genetic analyses of the ribosomal internal transcribed spacer ITS-2 and the mitochondrial cytochrome c oxidase 1 (cox1) gene fragments revealed the occurrence of four aporocotylid species (C. forsteri Cribb, Daintith & Munday, 2000, C. orientalis Ogawa, Tanaka, Sugihara & Takami, 2010, C. opisthorchis Ogawa, Ishimaru, Shirakashi, Takami & Grabner, 2011 and Cardicola sp.) in 421 Thunnus thynnus (L.) from the Western Mediterranean (274 fished from the wild and 147 from sea-cages). Cardicola opisthorchis was the most abundant species, with higher prevalence in the cage-reared fish than in those fished in the wild (21 vs 6%, p < 0.05). Adults of three species were recovered: C. forsteri from both gills and heart, C. opisthorchis from heart and C. orientalis from gills. The secondary gill lamellae were profusely infected by eggs of C. orientalis. A fourth species was found in four tunas, based on the molecular analyses of eggs apparently indistinguishable in size and shape from the eggs of C. orientalis. The findings provided evidence that infections with Cardicola spp. differed in relation to locality, host origin (wild vs cage-reared) and site of infection. It is necessary to estimate the possible different pathogenic effects of each species of Cardicola in order to take appropriate control measures.

Infections of nervous necrosis virus in wild and cage-reared marine fish from South China Sea with unexpected wide host ranges.

The concerns about the impact of the nervous necrosis virus (NNV) infections in wild fish have been raised. This paper presents the results of quarterly surveys of NNV in wild and cage-reared marine fish from South China Sea. Samples of 892 wild fish belonging to 69 species and 381 cage-reared fish belonging to 11 species were collected and were detected by seminested PCR and nested PCR. In the case of seminested PCR, the positive signal was detected in 3.0% and 3.1% samples of wild and cage-reared fish, respectively. However, by nested RT-PCR, the positive signal was observed in 42.3% and 63.0% samples of wild and cage-reared fish, respectively. If the fish species were considered, the positive signal was detected in 21.7% and 72.7% species of wild and cage-reared fish by seminested PCR assay, respectively. However, by nested RT-PCR, the positive signal was observed in 65.2% and 100% species of wild and cage-reared fish, respectively. The nucleotide sequences of the nested PCR products were determined. Phylogenetic tree showed that all the obtained viral isolates belonged to the red-spotted grouper nervous necrosis virus (RGNNV) genotype. Thirty-five species of the marine fish were the new hosts of NNV.

Biometric and metabolic profiles associated to different rearing conditions in offshore farmed gilthead sea bream (Sparus aurata L.)

Modern multivariate methods are applied to both biometric measurements and NMR metabolic profiling of fillet to discriminate farmed gilthead sea bream reared in different farming conditions. Two fish groups having the same average size, from the same farm, were caught in May and October. Biometric data demonstrate that condition factor is higher for the leaner fish, sampled in May, while liver somatic index is lower in fish sampled in October. Biometric features are related to metabolic changes that involve lipid storage from May to September, and their mobilization from muscle and liver during prespawning season (September, October). Structural phospholipids (phosphatidylcholine, phosphatidylethanolamine) and essential fatty acids (eicosapentaenoic and docosahexaenoic acids) characterize the lipid profile of the May catch, while triglycerides, monounsaturated and diunsaturated fatty acids, likely from absorption of vegetable oil components of feeds, suggest fish fattening in the warm season and discriminate fish caught in October. Among polar metabolites, taurine, glutamine, glycine, alanine, and creatine/phosphocreatine confirm their role as good biomarkers for the discrimination among fish produced in different farming conditions, especially involving feed digestion and metabolism, chronic stress, and alteration of energetic balance in cage-reared fish. Qualitative traits of farmed fish are therefore the result of a complex combination of environmental factors and farming practices, which should be analyzed to increase consumers' and farmers' awareness.

Microcystin bioaccumulation can cause potential mutagenic effects in farm fish

This study investigated the bioaccumulation of microcystin and its potential mutagenic effects in cage-reared fish. For six months, three reservoirs (Acauã, Cordeiro and Camalau) in arid regions of Brazil were monitored. After five months, 10 fish (Oreochromis niloticus) were collected from each tank, and the amounts of microcystin in their muscles and viscera were analysed. Mutagenic effects were also evaluated. Species of cyanobacteria were present during all months of our study. The highest biovolume of cyanobacteria and microcystin in water occurred in the Acauã Reservoir; this was followed by Cordeiro and Camalau. All fish sampled contained microcystin, ranging from 16.01 to 37.09ngg−1 in muscle and 228.2–804.0μgg−1 in liver. We observed significant differences between the micronucleus count in experimental and control fish (p<0.05), suggesting a potential mutagenetic effect in the experimental fish. In all reservoirs, the fish microcystin level was well above the World Health Organization (WHO) tolerable daily intake, indicating a serious risk to consumers.

Check list of the parasitofauna in Adriatic sea cage-reared fish

Along with the fast development of aquaculture in the Mediterranean, a number of emerging parasitic diseases was observed in cage-reared fish, which in confined rearing conditions induced mortality or/and indirect economical losses related to suppressed growth. The trend of diversification of aquaculture products and the introduction of new fish species in the rearing system, helped the introduction of new parasitic pathogens along with their host in the new environment. The process resulted in the adaptation of parasites and in a switch to resident aquaculture species (sea bass and sea bream) or/and increase of prevalence and abundance of parasites on newly introduced fish species. In both cases, the parasitofauna of reared fish even impoverished in terms of species richness and showed greater population values than in the wild fish population. Even if the Mediterranean parasitofauna of reared fish was the issue of numerous publications in the past decade, only occasional findings and reports concerned its specificities in the Adriatic Sea.

Parasite communities of Adriatic cage-reared fish

From June 2001 to March 2002, 7 semi-offshore facilities in the Adriatic Sea rearing sea bass Dicentrarchus labrax, sea bream Sparus aurata, sharpsnout bream Diplodus puntazzo and red sea bream Pagellus bogaraveo aged 1+, were monitored for the presence of protozoan and metazoan parasites. Obtained data sets of abundance and prevalence were used to evaluate the structure and dynamic of infra- and component parasite communities. In all hosts, except the red sea bream, dominant parasites were monogenean specialists, showing clear seasonality. Average infracommunity richness was very low, ranging from 1 to 3 parasites per fish, while at component community level, values ranged from 3 to 8, depending on host species. Based on low diversity indices and a moderate to high similarity coefficient between different facilities, it can be concluded that the parasitofauna of Adriatic cage-reared fish is a stable and impoverished stochastic assemblage, with monogeneans as the predominant parasitic group.

Increment patterns in otoliths and scales from mature Atlantic salmon Salmo salar

This is the first work to note a similarity in increment patterns between otoliths and scales up to maturation, helping to understand better the biological and physical mechanisms guid- ing otolith and scale growth and increment formation. We demonstrate, with returning 1- and 2-sea winter Atlantic salmon Salmo salar, that transverse otolith thin sections to the core expose increments that represent seasonal growth during the marine phase. These increments are similar to those that form on scales, albeit with greater increment-width variability. From cage-reared fish, we noted that the number of increments on otoliths and scales formed during the period of marine residence is the same, and that the average mean deposition-time is slightly over 1 wk in the first year and ca. 2 wk in the second year.

Quality characteristics of sharpsnout sea bream ( Diplodus puntazzo) from different intensive rearing systems

An experimental investigation was carried out on sharpsnout sea bream ( Diplodus puntazzo) reared in cage and in tank to evaluate the influence of the different culturing conditions on the nutritional quality of the fish. Fillets from fish of the same genetic origin and size, reared separately in tank and in cage, were analysed for proximate composition, inorganic elements, unsaponifiable lipid fraction compounds, fatty acid profiles of total, neutral and polar lipids and for textural properties. The proximate composition of differently-reared fish did not differ significantly except for the greater lipid content of the tank-reared specimens. High performance liquid chromatography of unsaponifiable lipids showed significantly higher levels of squalene, cholesterol and all- trans retinol in tank-reared fish fillets. Gas chromatography of total, neutral and polar lipids showed few differences between the fatty acid profiles of tank- and cage-reared fish. Firmness and amount of expressed liquid were also influenced by the rearing techniques.

Growth, Body Composition, and Organoleptic Evaluation of Channel Catfish Fed Diets Containing Different Percentages of Distillers' Grains with Solubles

Juvenile channel catfish (Ictalurus punctatus) were stocked in twelve 1.25-m3 floating cages at densities of 320 fish/m3 and fed to satiety twice daily for 110 d with one of four diets. Each diet contained a certain percentage (0, 10, 20, or 30%) of distillers 1 grains with solubles (DCS), which partially replaced soybean meal and corn. Individual weights of fish, survival, food conversion (FC, weight of feed given/weight gain by fish), and body composition (percentage moisture, protein, fat, and ash) of waste (head, skin, and viscera) and dressed carcasses were not significantly different (P > 0.05) among treatments. Fish fed a diet containing 10% DCS (mean individual total length, 26.7 cm) were significantly shorter (P 0,05) from fish fed diets with 0 and 20% DCS. Average individual weight was 219 g, survival was 92.1%, and FC was 1.6. Percentage fat (dry-matter basis) in the carcasses of cage-reared channel catfish averaged 38%. Organoleptic evaluation of fillets indicated that the fat complex flavor was of significantly higher intensity (P < 0.05) in cage-reared fish than in pond-raised fish. However, Organoleptic evaluation indicated that DCS impart no adverse taste to channel catfish. These data indicate that DCS can be used in a least-cost diet formulation for channel catfish at rates of up to 30%. This option allows feed producers flexibility in diet formulations for commercial catfish diets. Least-cost diet formulations offer economic ad- vantages in the preparation of a nutritionally com- plete diet by allowing change in diet formulations when ingredient prices fluctuate. Evaluation of al- ternative protein sources remains a high priority for fish nutritionists. Distillers' grains with solu- bles (DGS) are primary fermentation residues from

Three Years of Experience with a Channel Catfish Catchout, Pond in Illinois

Abstract A 0.2-hectare channel catfish, Ictalurus punctatus, catchout pond was operated for three fishing seasons to develop techniques beneficial to both angler and pond owner. During the first two seasons catfish were cage-reared to catchable size in the catchout pond and periodically released to replace fish caught by anglers. The larger and/or faster-growing catfish were more vulnerable to capture by hook-and-line angling than the smaller and/or slower growing individuals. During the second season cage-reared fish were released more frequently, while “hard-to-catch” fish were trapped or seined from the pond and caged for a week before returning them to the pond. Caging the fish for a short time did not improve catchability, but fish reared in cages were highly vulnerable to angling when released. During the third year largemouth bass, Micropterus salmoides, were stocked along with the catfish, and both species were maintained on a pellet diet. In 65 fishing days anglers harvested 90% of the catfish an...