Sea Cage Culture Research Articles

Experimentally induced marine flexibacteriosis in Atlantic salmon smolts Salmo salar. II. Pathology

The fish disease marine flexibacteriosis is characterised by necrotic lesions on the body, head, fins, and occasionally gills, with erosive lesions on the external surface as the prominent clinical sign. In Australia, the main species affected are Atlantic salmon Salmo salar and rainbow trout Oncorhynchus mykiss in sea-cage culture in Tasmania. Using a dose-dependent trial to determine pathology, 2 forms of the disease were noted in Atlantic salmon. The acute form occurs within 2 to 3 d after inoculation at high doses (1 x 10(8) cells ml(-1)) and is characterised by the disintegration of the epithelium. The chronic form of the disease began as small superficial blisters of the epidermis, which develop into ulcerative lesions that leave musculature exposed. The predominant lesion sites were the dorsum and pectoral fins. Jaws were commonly affected, and gill necrosis was also noted. Behaviour of Atlantic salmon as well as the conditions under which they were kept contribute to the size and distribution of lesions observed. Lack of an inflammatory response in pathology and rapid and destructive mortalities observed in higher inoculum doses suggested a role of toxins in the pathogenesis of Tenacibaculum maritimum. This is the first study to examine the development of marine flexibacteriosis lesions and to utilise immunohistochemistry to verify that the bacteria observed in histology was T. maritimum.

Effect of extracellular products of Tenacibaculum maritimum in Atlantic salmon, Salmo salar L.

Keywords: Atlantic salmon, extracellular products, LD50, Tenacibaculum maritimum, toxins. Tenacibaculum maritimum (formerly Flexibacter maritimus) is a well-known pathogen in a number of cultured fish species worldwide (Wakabayashi, Hikida & Masumura 1986; Alsina & Blanch 1993; Chen, Henry-Ford & Groff 1995; Handlinger, Soltani & Percival 1997; Ostland, LaTrace, Morrison & Ferguson 1999). It is a marine bacterium that causes necrotic lesions on the body, head, fins and gills, with erosive lesions on the external surface as the prominent clinical sign (Carson, McCosh & Schmidtke 1992). In Australia, the main species affected are Atlantic salmon, Salmo salar L., and rainbow trout, Oncorhynchus mykiss (Walbaum), in sea-cage culture in Tasmania (Handlinger et al. 1997). Experimental investigation into the pathogenesis of T. maritimum showed that challenge at higher doses (c. 1 · 108 cells mL)1) had an acute lethal effect on Atlantic salmon (van Gelderen 2007). Mortalities occurred within days and the clinical sign was the disintegration of the epithelium. In addition, a lack of an inflammatory response is characteristic of early flexibacteriosis lesions. Handlinger et al. (1997) suggested that this was the result of powerful exotoxins that prevent a host response. These findings pointed to a possible role of toxins in the pathogenicity of T. maritimum in Atlantic salmon. Effects of T. maritimum toxins have been explored in red and black sea bream, Pagrus major (Temminck and Schlegel), and Acanthopagrus schlegeli (Bleeker) (Baxa, Kawai & Kusuda 1988). In both fish species, extracellular products (ECP) showed insignificant in vitro activity; however, this did not correspond with the toxic effects observed in vivo with ECP recording the lowest LD50. Baxa et al. (1988) did indicate that the pathogenicity of T. maritimum in black and red sea bream may be ascribed in part to ECP. The current study investigated ECP toxicity in vivo to observe direct effects rather than in vitro activity of different toxins. Further, this study provides the first observations of T. maritimum ECP toxicity in Atlantic salmon.

Stable isotope determination in wild and farmed gilthead sea bream ( Sparus aurata) tissues from the western Mediterranean

Stable isotopes of carbon and nitrogen ( δ 13C and δ 15N) have been determined in wild and farmed gilthead sea bream ( Sparus aurata) samples of white and red muscle, liver, gills and gonads. First, δ 13C and δ 15N values were determined in samples with and without lipid removal to check the possible effect of lipid content on the stable isotope values of the different tissues studied. Differences were found for δ 13C in all tissues studied apart from white muscle of wild fish, the tissue with the lowest lipid content. For δ 15N values no differences were found in wild fish tissues. Liver from farmed fish showed lower δ 15N value after lipid removing. Further conclusions were based on results obtained from lipid-free samples. δ 13C of cultured fish tissues showed a mean depletion of 2.9 ± 0.4‰ compared to wild specimens, suggesting different sources of carbon in the diet, probably due to the feed used during sea-cage culture. Cultured gilthead sea bream tissues were significantly more enriched in nitrogen than wild specimens by an average of 1.5 ± 0.2‰ in white muscle, indicating a slight increase in the trophic level. Determination of stable isotope signatures of gilthead sea bream tissues allows clear discrimination between wild and cultured sea bream, and characterisation of differences in diet and feeding conditions in any tissue studied.

Advances in the culture of striped trumpeter larvae: A review

Striped trumpeter, Latris lineata, was chosen as the best new candidate for sea cage culture in Tasmania in the late 1980s. It has a complex and extended post-larval or ‘paperfish’ stage lasting up to 9 months and has historically proven difficult to culture. Excellent progress has been made in understanding and controlling reproduction and broodstock are spawned year-round through photothermal control. Problems with early larval rearing have been overcome and egg incubation and early larval rearing protocols have been established. A mortality peak associated with first feeding has been reduced using better live feed production techniques and improved water quality. Using antibiotics showed that high bacterial loads were an important factor in larval mortality. A new water filtration and ozonation system has removed the need for antibiotics. Larval nutrition research focused on the link between potential deficiencies or imbalances in the three essential PUFA in live feeds: docosahexaenoic acid, eicosapentaenoic acid and arachidonic acid. Novel experimental emulsions were applied with dose response experimental designs to identify the dietary requirement for selected PUFA and vitamins. Despite the advances in live feed enrichments, the live feeds, particularly Artemia, were found to have sub-optimal lipid profiles. Copepods were cultured, as a supplement to traditional live feeds, and improved larval rearing success. Costs to scale-up production and to control extensive cultures presently restrict the usefulness of copepods. Important breakthroughs have occurred in health with the detection and control of nodavirus, myxozoan and bacterial disease. Ozone disinfection of eggs and sterilisation of hatchery seawater have been important control measures. Another bottleneck to production has been mortality of larvae from notochord flexion to metamorphosis. System changes to reduce nocturnal movements and a better understanding of optimal live feed densities, and weaning onto formulated diets, have improved survival and growth. High rates of jaw malformation remain a challenge and no definitive cause has been established. Reduced rates of malformations have been associated with one or a combination of high feed rates, lower larval densities and temperatures, and reductions in ‘walling’ behaviour. Future research is aimed at finding ways to reduce malformations, develop probiotics and early weaning strategies, control parasites and scale-up production to assess performance of juveniles in sea cages.

The effect of different holding systems and diets on the performance of spiny lobster juveniles, Jasus edwardsii (Hutton, 1875)

This study evaluated the growth and survival of lobster juveniles over 8 months when fed fresh Perna canaliculus mussel and stocked at a density of 35 ind. m − 2 in one of three holding systems: a prototype sea-cage design, a commercial sea-cage design, and small experimental land-based holding tanks. At the same time the growth, survival and nutritional condition of lobsters fed fresh mussel in the prototype sea-cages were compared with lobsters feeding only on the biofouling of the sea-cages or fed two artificial diets (dry and moist) three times a week. Survival in the prototype sea-cages (83.3 ± 2.3%) was similar to the experimental flow-through tanks (87.9 ± 8.0%) but significantly higher than the commercial sea-cage (55.4 ± 1.8%). Furthermore, the prototype sea-cages resulted in significantly higher specific growth rate (SGR = 0.96% BW day − 1 ) than the other system designs (flow-through tank SGR = 0.86 BW day − 1 and commercial sea-cage SGR = 0.77% BW day − 1 ). The growth rate in the prototype sea-cages was one of the fastest ever recorded for this species, over this size range of juveniles (3–31 g) and at comparatively low seawater temperatures (15.2 °C). The survival of lobsters in the prototype sea-cages did not differ between the three experimental feeding regimes. However, growth when feeding on biofouling alone or with the addition of artificial diets was comparatively inferior to the lobsters fed mussels (SGR = 0.96% BW day − 1 ; survival = 83.3 ± 2.3%). Lobsters fed the dry formulated diet (SGR = 0.78% BW day − 1 ; survival = 79.3 ± 1.2%) grew significantly faster than on the moist formulated diet (0.60% BW day − 1 ; 59 ± 17.8%) or on the biofouling only (0.38% BW day − 1 ; 66.3 ± 4.9%). The growth of lobsters fed the dry formulated diet in the prototype sea-cage was better than in previous tank growth studies using experimental diets and was probably attributable to animals feeding on biofouling of the sea-cages. Digestive gland histology supported the growth trends, with lobsters fed fresh mussel and the dry formulated diet being in best nutritional condition at the end of the growth experiment. The results indicate that sea-cage culture of juvenile spiny lobsters can provide significant growth advantages over tank systems possibly due to supplementary nutrition from biofouling. However, sea-cage structural design, feeding and diet type are important factors influencing the performance of J. edwardsii juveniles in sea-cages.

Review of captive bred species and fry production of marine fish in China

The artificial breeding of marine fish in China has been developed over a period of more than 50 years. Both species diversity and fry production have greatly increased since the 1980s. By the year 2000, at least 52 species belonging to 24 families of marine fish had been successfully bred. Large quantities of cultured fry can meet the needs of both sea cage culture and pond culture for most species. Fish fry production has entered a period of sustainable development. The number of artificially produced fry of large yellow croaker ( Pseudosciaena crocea) exceeded 1.3 billion in year 2000. The species for which more than 10 million fry is produced annually through aquaculture are: red drum ( Sciaenops ocellatus), Japanese sea perch ( Lateolabrax japonicus), redeye mullet ( Liza haematocheila), cuneate drum ( Nibea miichthioides), red seabream ( Pagrosomus major), milkfish ( Chanos chanos) and three-banded sweetlip ( Plectorhynchus cinctus). Several millions of artificial fry are cultured annually for the following species: Japanese flounder ( Paralichthys olivaceus), black porgy ( Sparus macrocephalus), silver sea perch ( Lates calcarifer), Russell's snapper ( Lutjanus russelli), javelin grunt ( Pomadasys hasta), miiuy croaker ( Miichthys miiuy), Chinese black sleeper ( Bostrichthys sinensis) and skewband grunt ( Hapalogenys nitens). Fishes belonging to the family Sciaenidae are now the major species for artificial propagation.

Technical Responses to Challenges in Milkfish Aquaculture

Milkfish (Chanos chanos) has been cultured in Asia for centuries. In 1999 the total world production of cultured milkfish was estimated at 381,930 metric tons. To meet the production target with less available land for farming, traditional culture in shallow-water ponds, which relied on wild-caught fry from coastal waters and on benthic algae as the main food, had to be modified. To increase unit production, a deep-water pond culture system was developed in the mid-1970s. As a result of the increased water depth and stocking density, in addition to the use of formulated feed and aeration devices, unit production underwent a 5- to 8-fold increase. In the Philippines, pen and sea cage culture methods were developed to increase production. The life cycle of milkfish was completed in captivity before technology for mass production in the hatchery was established in the late 1980s. Preventing overproduction of milkfish is currently an important issue in milkfish producing countries. IThe improvement in processing technology, the diversification of products, and the establishment of international marketing networks are important challenges to the industry. The extension of milkfish aquaculture technology to other countries is a goal that may greatly benefit mankind.

Treatment of spionid mud worm ( Boccardia knoxi Rainer) infestation of cultured abalone

Early attempts at sea cage culture of blacklip abalone ( Haliotis rubra Leach) in southern Tasmania, Australia were characterised by infestation with spionid polychaetes, commonly Boccardia knoxi. Large numbers of mud worms were associated with severe blistering and stock mortality. Immersion treatment using chemotherapeutics and air-drying treatment was tested for efficacy in eliminating mud worms and lethality to abalone. Air drying of spionid-infested abalone for 2–4 h at <64% humidity significantly reduced infestation levels of two species of spionid polychaetes. Such treatment produced no abalone mortality in the short term, and 100% of 40 mm H. rubra dried for 11 h survived a 54-day posttreatment observation period. Treatment air drying suppressed abalone growth in the long term in one of three trials. Such treatment is considered worthwhile in cases of heavy spionid infestation.

Sea-cage culture of the spiny lobster Jasus edwardsii in New Zealand

The potential for using suspended sea cages for the aquaculture of juvenile spiny lobsters was assessed for Jasus edwardsii in New Zealand. Lobsters were grown for a year in sea cages at three sites starting from pueruli and regularly fed on opened mussels. Larger juvenile lobsters of two size classes were also held in sea cages with small live mussels for food. Pueruli grew at rates that were close to or greater than those previously recorded from tank experiments. At the most northern site, lobsters grew most quickly to an average of 42.1 mm CL 0.4 s.e. and 36.9 g wet weight 1.0 s.e. in a year. The mortality of lobsters differed with site, but at one site was lower (14%) than was recorded in a previous tank-culture experiment (25%). The differences in growth and mortality among sites appear to be related to differences in ambient water temperatures. Larger juvenile lobsters were found to be unable to feed on the small live mussels. These results indicate that suspended sea-cage culture has considerable potential for the aquaculture of spiny lobster juveniles but will require the careful selection of sites and the development of effective feeding arrangements.

Economic Feasibility of Aquaculture of Spiny Lobsters Jasus edwardsii in Temperate Waters

AbstractAround the world there is strong interest in the aquaculture of spiny lobsters (family Palinuridae). However, there is little published information about the economic feasibility of spiny lobster aquaculture. For more than 20 yr there has been experimental grow out of the spiny lobster Jasus edwardsii in New Zealand in land‐based systems using seed animals (puerulus) taken from the wild. These studies provide sufficient information on growth, mortality, food conversion, handling and capital costs to enable an assessment of the economic feasibility of the commercial culture of spiny lobsters in temperate waters. This assessment suggests that profitable spiny lobster aquaculture will rely on greatly reducing the infrastructure and operating costs of land‐based farming operations, as well as lowering feed and labor costs. Financial simulations suggest that increasing productivity through faster growth rates and lowered culture mortalities will only have a minor effect on profitability unless infrastructure and operating costs can be reduced significantly. Seacage culture or sea ranching of spiny lobsters may offer a means of avoiding high infrastructure costs associated with land‐based farming operations. The development of a cost‐effective artificial feed would also appear to be a priority for improving the economic outlook for culturing spiny lobsters. The results of this study are relevant to the economics of spiny lobster culture developments in other temperate regions of the world.

Predicting aquaculture waste from gilthead seabream ( Sparus aurata) culture using a nutritional approach

A model to estimate the waste production from sea cage culture was established. Using known feed inputs of nitrogen, phosphorus and organic matter, the model quantifies waste discharge from seabream culture. Daily feed intake and growth in Sparus aurata fed a commercial diet with known composition were measured and found to be dependent on fish weight and water temperature. Digestibility of the commercial feed was measured using chromic oxide as a marker and collection of feces by stripping. The proximate composition of Sparus aurata at different sizes was determined and nitrogen and phosphorus content were on average 28.5 and 7.2 g·kg −1 body mass, respectively. Excretion of ammonia-nitrogen and inorganic phosphorus after metabolic processes was calculated as the difference.