Open Sea Cages Research Articles

Spatio-temporal variability of ichthyophagous bird assemblage around western Mediterranean open-sea cage fish farms

Ichthyophagous birds aggregate at cage fish farms attracted by caged and associated wild fish. Spatio-temporal variability of such birds was studied for a year through seasonal visual counts at eight farms in the western Mediterranean. Correlation with farm and location descriptors was assessed. Considerable spatio-temporal variability in fish-eating bird density and assemblage structure was observed among farms and seasons. Bird density increased from autumn to winter, with the great cormorant being the most abundant species, also accounting largely for differences among farms. Grey heron and little egret were also numerous at certain farms during the coldest seasons. Cattle egret was only observed at one farm. No shags were observed during winter. During spring and summer, bird density decreased markedly and only shags and little egrets were observed at only a few farms. Season and distance from farms to bird breeding/wintering grounds helped to explain some of the spatio-temporal variability.

Optimization of the stocking parameters for mud spiny lobsterPanulirus polyphagus(Herbst, 1793) capture-based aquaculture in tropical open sea floating net cages

Mud spiny lobsters, Panulirus polyphagus (Herbst, 1793), were reared at four different stocking sizes and stocking densities in open sea cages to evaluate their effects on growth performance. To evaluate the effect of stocking size on the growth performance, the lobsters were segregated into four different treatment groups according to size and were stocked at a density of 300 animals per cage. To evaluate the effect of stocking density on the growth performance, lobsters of 81–100 g were stocked in four different stocking densities, i.e. 16/m2, 24/m2, 32/m2 and 40/m2. The results showed that the growth rate of (60–80 g) size group, was significantly higher compared to the size groups, i.e. 101–120 g and 121–140 g comprising of larger individuals. The final body weight, though significantly higher in 81–100 g as compared to 60–80 g, the growth performance (i.e. weight gain percentage (WG %) and specific growth rate (SGR)) were not significantly different. The density‐dependent influence on growth performance was evident in this study. The WG % and SGR during 90 days’ culture period was significantly higher in 24/m2 compared to other groups. This study provides crucial information about the appropriate stocking density and stocking size of lobsters at the field level, which would help to promote sustainable lobster cage farming by maximizing the production potential of the system.

The oxygen threshold for maximal feed intake of Atlantic salmon post-smolts is highly temperature-dependent

In order to maximize the growth potential of Atlantic salmon (Salmo salar L.) in the on-growing phase in open sea cages, the dissolved oxygen (DO, % of air saturation) level must exceed the minimum DO required for maximal feed intake (DOmaxFI). The main aim of this study was to determine the effect of temperature on this important threshold DO, and secondly, to provide aquaculturists with a model that estimates feed intake as function of both temperature and DO. Quadruple tank groups of Atlantic salmon post-smolts (~0.3–0.5kg) were kept at 7, 11, 15 and 19°C, and subjected to seven DO levels per temperature, ranging from ≈32–92, 42–102, 52–112 and 62–122% O2, respectively, for 42days. DO levels were changed every second day, in random order. Fish were fed a known amount of feed in excess twice daily, waste feed was collected and daily feed intake (DFI, % of biomass, BM, per day) estimated. The routine oxygen consumption rate (MO2 rout, measured in partially fasted and active fish) and the DO below which MO2 rout started to decline (termed the routine limiting oxygen saturation, LOSrout) was determined in fasted fish at all four temperatures at the end of experimentation, and the latter was used to estimate the “zero feed intake DO” in the DFI model. The data demonstrate sustained appetite with decreasing DO until a threshold level (DOmaxFI) is reached, at which point appetite gradually decreases. Both the maximal level of feed intake (DFImax) and the DOmaxFI were highly dependent on temperature, increasing from 0.47 to 0.88% of BM/day, and from 42 to 76% O2, respectively, within the temperature range tested. The LOSrout ranged from 24 to 40% O2. The present study is the first to present the pronounced effect of temperature on DOmaxFI, and results suggest that the DO requirement of A. salmon has previously been considerably over-estimated, particularly at lower temperatures. Statement of relevanceThe study links growth performance to environmental temperature and oxygen.

Grow-out culture of abaloneHaliotis tuberculata coccineaReeve, fed land-based IMTA produced macroalgae, in a combined fish/abalone offshore mariculture system: effect of stocking density

Haliotis tuberculata coccinea has been identified as a target species for European aquaculture development, in order to fulfil the rising demand for abalone. The effects of different stocking densities on the growth performance, feed utilization and survival of two different initial size groups (30 and 40 mm) of abalones, during the final grow-out to cocktail/market size (45–60 mm), were determined over a 6-month period. Trials were performed in abalone cages installed in a commercial open-sea cages fish farm. Animals were fed the red algae Gracilaria cornea and the green one Ulva rigida, both obtained from a land-based integrated multi-trophic aquaculture system. Survival rates were very high (94–98%) regardless the density employed. Sustained high linear growth was recorded both in shell and weight. However, a 17–19% reduction in weight gain was obtained by doubling the initial stocking density, suggesting a higher competition for space or food. Nevertheless, the high growth performance (70–94 μm day−1; 250–372% weight gain) and survival attained, even at high densities, denoted the suitability of the offshore mariculture system as well as the biofilter produced macroalgae for grow-out culture of H. tuberculata coccinea that overall could reach cocktail/commercial size in only 18–22 months.

Chronic stress due to high stocking density in open sea cage farming induces variation in biochemical and immunological functions in Asian seabass (Lates calcarifer, Bloch)

Stocking density is an important factor in cage aquaculture of finfish. Effects of high stocking density (35 fishcubicm(-1)) on a range of biochemical and immunological parameters in Asian seabass reared in open sea floating net cages were compared to fish held in relatively low density (15 fishcubicm(-1)). The results revealed that chronic stress due to high stocking density induced variations in most of the parameters studied as evidenced by increased cortisol and glucose levels and decreased activity of lysozyme, myeloperoxidase and complement. Production of reactive oxygen species, total leucocyte count and total serum protein were also decreased, whereas anti-protease, alkaline phosphatase and acid phosphatase activities were increased in high stocking-density group when compared to low stocking-density group. Effects of chronic stress due to high stocking density were discussed in relation to variations in these parameters.

Does fin damage allow discrimination among wild, escaped and farmed Sparus aurata (L.) and Dicentrarchus labrax (L.)?

Summary The present study compares fin damages in gilthead seabream (Sparus aurata) and European seabass (Dicentrarchus labrax) according to their wild, escaped or farmed origins. In addition, the potential applicability of fin condition indices (Fin Erosion Index ‘FEI’ and Fin Splitting Index ‘FSI’) as identification tools is discussed. Farmed seabream fins evidenced more erosion and splitting (FEI ± SD: 2.1 ± 0.3; FSI ± SD: 1.9 ± 0.6) than wild seabream fins (FEI: 0.8 ± 0.6; FSI: 1.2 ± 0.9), a result of farming conditions in open-sea cages. Escaped seabream fin erosion was between that of farmed and wild seabream (FEI: 1.6 ± 0.4), which could indicate that fins in farmed fish recover over time from farming abrasions once they are in the wild. However, the fins of escaped seabream seem to be weaker than those of the wild fish, and therefore might be more susceptible to suffer other types of erosion such as splitting or nipping (FSI: 2.3 ± 0.7). No significant differences were found in seabass FEI according to their origins, although wild seabass presented significantly more split caudal fins (FSI: 3.3 ± 2.8) than the farmed seabass (FSI: 1.2 ± 1.1) and escapees (FSI: 2.5 ± 1.6). Therefore, FEI for seabream could be used as tools not only to distinguish between wild and farmed fish, but also to identify recent escapees, improving further assessments on the contribution of seabream escapees in fishery landings. However, the healing potential of damaged fins must be considered for the proper identification of escapees. Use of fin condition indices from both species could be helpful for aquaculture management, to assess fish welfare in fish farms stocks, and improve the knowledge of handling, stock densities and open-sea cage environment conditions.

Vibrio alginolyticusinfection in Asian seabass (Lates calcarifer, Bloch) reared in open sea floating cages in India

Asian seabass (Lates calcarifer) has been designated as a candidate species for open sea cage culture in India. A case of vibriosis in Asian seabass reared in open sea floating cages is reported. Haemorrhage and ulcer were observed grossly in the diseased fish. The pathogen, identified as Vibrio alginolyticus based on biochemical and molecular characterization, was isolated from liver, gill, kidney, brain and blood. Histological examination of the diseased fish showed congestion, haemorrhage and necrosis in vital organs. The LD50 studies showed that the organism was virulent to Asian seabass, and the LD50 value was 103.2 CFU g−1 fish.

Infection Dynamics of Microsporidium seriolae (Microspora) Causing the Beko Disease of Seriola spp.

Infection dynamics of Microsporidium seriolae causing the beko disease of yellowtail Seriola quinqueradiata and amberjack S. dumerili were investigated at fish farms and an experimental facility. A 4-year survey (2006-2009) showed a sharp increase in prevalence of infection with M. seriolae in June or July soon after stocking net cages with yellowtail and amberjack wild fingerlings. Most cysts blackened and finally disappeared in November in the following year. However, in 2006 when the levels of infection were relatively high, some visible cysts still remained even in autumn of the following year. Infective periods and effects of fish size on M. seriolae infection were investigated via natural exposure of hatchery-reared yellowtail juveniles by transferring to an open sea cage in an endemic area. Invasion of the parasite into fish occurred in June and July but not after the mid-August. A comparison of M. seriolae infection among four size classes of yellowtail showed that the smallest fish (1 g in mean weight) had the lowest prevalence of infection.

Nitrogen budgets for the areolated grouper Epinephelus areolatus cultured under laboratory conditions and in open-sea cages

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 186:271-281 (1999) - doi:10.3354/meps186271 Nitrogen budgets for the areolated grouper Epinephelus areolatus cultured under laboratory conditions and in open-sea cages K. M. Y. Leung*, J. C. W. Chu, R. S. S. Wu** Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, China *Present address: Institute of Biomedical and Life Sciences, Graham Kerr Building, University of Glasgow, Glasgow G12 8QQ, Scotland, UK **Addressee for correspondence. E-mail: bhrswu@cityu.edu.hk ABSTRACT: The nitrogen budget of grouper Epinephelus areolatus (Forskål) in a culture system can be represented by the mass balance equation: consumption (C) = feed input (I) - feed wastage (W) = production (P) + mortality (M) + excretion (E) + faecal production (F). A nitrogen budget was constructed for individual groupers cultured for 1 mo under laboratory conditions; and an annual nitrogen budget was also constructed for a cohort of E. areolatus cultured in an open-sea-cage farm and fed with trash fish. Consumption was determined independently both by feeding experiments as well as by summation of P, M, E and F, to provide an estimate of the accuracy of the budget equation. In the laboratory budget, 27.5% of N consumed was channelled to growth, while 64.4% was excreted in the form of ammonia and 8.1% lost in faeces. The N-assimilation efficiency was 91.9%, while the net N-retention efficiency was 29.9%. For the annual budget constructed for the open-sea-cage farm, only 8.6% of total N input into the farm was harvested in the form of fish production, while loss to mortality was 3.7%. Ammonia excretion was the most important N loss (46.0%), followed by feed wastage (37.7%) and faecal production (4.0%). 66% of total N input could be accounted for in the laboratory N budget for individual groupers, but only 48% of N input into the culture system could be accounted for in the annual nitrogen budget constructed for open-sea-cage farming. It was estimated that 87.7% of the total N input to the farm was lost to the environment (equivalent to 321 kg N t-1 of fish production). Such a value is almost 3 times as high as N loss from temperate salmonid farms. KEY WORDS: Nitrogen budget · Assimilation efficiency · Grouper Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 186. Publication date: September 17, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.