Use of night-lights to attract food organisms into tropical marine fish cages

Abstract. A 91-day cage trial was conducted with juvenile seabass, Lates calcarifer (Bloch), and grouper, Epinephelus tauvina (Forskal), to ascertain the capacity of kerosene pressure lamps and fluorescent electric lamps as night-lights above the cages to attract pelagic food organisms into the cage and consequently sustain the survival and growth of the cultured fish. The experiment was conducted using 1×1×1·5m floating cages with three different net mesh sizes (1, 13, and 19mm) and four fish stocking densities (seabass—10, 20,30 and 40/m³; grouper —10/m³). A positive growth response and survival was observed with seabass and to a lesser extent with grouper with increasing net mesh size and decreasing fish stocking density. At the lowest tested density of 10 fish/m³ seabass survival increased from 5·0 to 95·0% and total cage fish biomass increased from −95·1% to +56·9% with an increase in net mesh size from 1 to 19mm over the 91-day culture trial, respectively. The results are discussed in relation to the current commercial marine finfish cage farming practices employed in Indonesia.     

Swimming behaviour as an indicator of low growth rate and impaired welfare in Atlantic halibut (Hippoglossus hippoglossus L.) reared at three stocking densities

The Atlantic halibut (Hippoglossus hippoglossus L.) is a new species in Norwegian aquaculture. However, in ongrowing trials, halibut shows variable and generally poor rates of growth. The halibut is a flatfish that spends most of its time resting on the bottom, and it was hypothesized that high stocking densities with frequent social interactions could lead to behaviour changes, reduced appetite and impaired welfare. Halibut were kept in six tanks at low, medium, and high densities (18%, 54% and 112% bottom coverage). All fish were individually tagged with Trovan™ passive implant transponder (PIT) tags, allowing an antenna to register fish swimming at the surface. Swimming and feeding behaviour was also recorded by underwater video cameras. Individual growth rates were highly variable, but food consumption and growth rates fell significantly with increasing stocking density, while individual swimming activity rose with increasing density. Frequent “surface swimmers” had a significantly lower growth rate than fish that were seldom recorded by the PIT antennae. Surface swimming may therefore be an indicator of suboptimal growth rates and impaired welfare in reared halibut.     

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.     

Effect of feeding delay after self‐feeder activation on growth performance and feeding behaviour of red porgy (Pagrus pagrus L. 1758): application to submergible cages with surface hopper

Red porgies (Pagrus pagrus) of 20.6±1.5 g mean weight were reared in tanks under four delayed self‐feeding conditions (0=control, 7, 30 and 90 s) after rod activation. The time intervals were chosen to simulate the time taken for a commercial pelleted feed to transit the tube linking a surface‐mounted feed hopper and the depth at which a cage might be submerged. Daily feeding rate, growth, food conversion index and condition factor were quite similar but fish behaviour differed among conditions. Fish remained close to the feeding point in the first two treatments (0 and 7 s delay) but foraged more widely in the remaining treatments (30 and 90 s delay), only reconsolidating around the feeding point a few seconds before feed was released. Results are discussed in relation to learning capacity and adaptation of fish to feeding behaviour flexibility, in order to develop reliable self‐feeding systems suitable for submerged cages.     

Comparative composition and shelf-life of fillets of wild and cultured turbot (Scophthalmus maximus) and Atlantic halibut (Hippoglossus hippoglossus)

Turbot and Atlantic halibut are highly valued fish species. However,very little is known about fillet shelf-life characteristics associated withboth species. Thus, fillet -tocopherol content and proximate compositionof wild turbot (1.5 kg) and Atlantic halibut (1.1 kg)caught off the south coast of Ireland and the north-west coast of Iceland,respectively, were investigated. In addition, the susceptibility of fillets, storedunder retail conditions, to lipid oxidation and colour change was studied.Proximate composition analysis showed that turbot had significantly highermoisture (P < 0.001) and lower protein (P < 0.001) contents compared toAtlantic halibut. Atlantic halibut incorporated significantly higher (P <0.001) levels of -tocopherol into fillets than turbot. Over 14 days ofstorage on ice, fillets from Atlantic halibut exhibited significantly lower (P =0.020) levels of lipid oxidation than those of turbot. However, malondialdehyde(MDA) concentrations were generally very low, never exceeding 0.6 gg^–1 fillet. Turbot maintained a significantly higher (P< 0.001) pH over the storage period. The lightness (L^* values) offillets from both species increased over 14 days of storage, but wassignificantly higher (P < 0.001) in Atlantic halibut than in turbot. Turbotdeveloped a relatively intense yellow colour during storage (decrease in hueangle and increase in b^* values), whereas this was not the case forAtlantic halibut. The results of this study demonstrate that fillets of wildAtlantic halibut stored on ice, were less prone to lipid oxidation anddiscolouration than those of wild turbot. However, quality changes in turbotwere very small showing that both fish have tremendous shelf-life capacities interms of lipid oxidation. These findings are considered in the context of knownmaterial for farmed fish.     

波浪作用下双层网底鲆鲽网箱水动力特性的数值模拟

根据有限单元法建立了波浪作用下双层网底网箱的受力运动模型,通过数值计算求解双层网底的位移与倾角。先将上层网底与下层网底的计算值进行比较,然后,将双层网底网箱中下层网底与单层网底网箱开展对比分析。计算结果显示,在波浪周期内,双层网底网箱的2层网底能保持相对平行的状态。2层网底的位移与最大倾角随着波高与周期的增大而增加,并且2层网底的倾斜方向一致。在相同波浪条件作用下,下层网底的水平位移大于上层网底,二者垂直位移差异较小,下层网底最大倾角值大于上层网底。研究发现,当波高为15 cm、周期为1.4 s时,双层网底网箱的2层网底的倾角相差最大,但并未发生接触碰撞,网底可以保持相对稳定。此外,双层网底网箱的下层网底的最大位移值小于单层网底网箱,最大倾角值大于单层网底网箱。研究表明,当波浪一定时,双层网底网箱的最大锚绳力均大于单层网底网箱。     

Stocking density and welfare of cage farmed Atlantic salmon: application of a multivariate analysis

The welfare of fish is receiving increasing attention and attempts have been made to control welfare in farmed fish through regulation of management practices, including stocking density. However, there is little published information on the influence of stocking density on welfare of fish in marine cages. This present study examined welfare in Atlantic salmon (Salmo salar) in cages on a commercial marine farm, exposed to densities ranging from 9.7 to 34 kg m⁻³. On three occasions over a period of 10 months, fish were sampled from each cage, weighed and measured; their fin condition assessed and blood samples taken for measurement of glucose and cortisol. A multivariate analysis was used to combine four commonly used measures of fish welfare (condition of body and fins and plasma concentrations of glucose and cortisol) into a single welfare score. As well as objectively reflecting a coherence within the data, this score was consistent with the evaluation of welfare by experienced farmers. A generalized linear model indicated that the median welfare score for each cage was significantly related to sampling period, to stocking density (mean over the previous 3 months) and to location of the cage. A model with all the data from individual fish proved to be more robust and also identified sample period, stocking density (mean over 3 months) and position of the cage as significant predictors of the welfare score. There was no significant association between the welfare score and the length of time since grading or lice treatment. Further analysis of the relationship between stocking density and the welfare score suggested that there was no trend up to an inflection point ca. 22 kg m⁻³, after which increasing stocking density was associated with lower welfare scores. This study suggests that, while stocking density can influence the welfare of Atlantic salmon in production cages, this is only one influence on their welfare and on its own cannot be used to accurately predict or to control welfare.     

Submerged light increases swimming depth and reduces fish density of Atlantic salmon Salmo salar L. in production cages

Artificial photoperiods that postpone sexual maturation and increase growth are now widely used in the Atlantic salmon Salmo salar L. farming industry. Few studies have been carried out to examine the effect of this treatment on fish behaviour and welfare in production cages. In this study, echo‐integration was used to observe the swimming depth and fish density of salmon in 20‐m‐deep production cages illuminated by lamps mounted above the water surface (SURF) or submerged in the cage (SUBS). From January to May, SUBS swam at a greater depth (5–11 m) than SURF (1–3 m) at night. SURF descended and SUBS ascended at dawn, but SUBS were still swimming at greater depth than SURF during the day from January to March. The difference in swimming depth resulted in SURF swimming at a median fish density about twice as high as SUBS at night and up to five times the calculated fish density. SURF increased the utilization of the cage volume as the biomass increased, but fish swimming at the highest density did so at up to 20 times the calculated fish density. The results suggest that salmon position themselves in relation to the artificial light gradient to maintain schooling behaviour and that the use of submersible lights may be a precaution to secure the welfare of caged salmon.     

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.     

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.     

Growth, feed conversion and chemical composition of Atlantic salmon (Salmo salar L.) and Atlantic halibut (Hippoglossus hippoglossus L.) fed diets supplemented with krill or amphipods

The effects of partial replacement of fish meal (FM) with meal made from northern krill (Thysanoessa inermis), Antarctic krill (Euphausia superba) or Arctic amphipod (Themsto libellula) as protein source in the diets for Atlantic salmon (Salmo salar L.) and Atlantic halibut (Hippoglossus hippoglossus L.) on growth, feed conversion, macro‐nutrient utilization, muscle chemical composition and fish welfare were studied. Six experimental diets were prepared using a low‐temperature FM diet as control. The other diets included northern krill where 20, 40 or 60% of the dietary FM protein was replaced with protein from northern krill, and two diets where the FM protein was replaced with protein from Antarctic krill or Arctic amphipod at 40% protein replacement level. All diets were iso‐nitrogenous and iso‐caloric. Atlantic salmon grew from 410 g to approximately 1500 g during the 160 day experiment, and Atlantic halibut grew from 345 g to 500–600 g during the 150 day experiment. Inclusion of krill in the diets enhanced specific growth rate in salmon, especially during the first 100 days (P < 0.01), and in a dose–response manner in halibut for over the 150 day feeding period (P < 0.05). Feed conversion ratio did not differ between dietary treatments, and no difference was found in dry matter digestibility, protein digestibility and fish muscle composition. Good growth rates, blood parameters within normal ranges and low mortalities in all experimental treatments indicted that fish health was not affected either Atlantic salmon or Atlantic halibut fed the various zooplankton diets.     

Appetite, gut transit, oxygen uptake and nitrogen excretion in captive Atlantic halibut, Hippoglossus hippoglossus L., and lemon sole, Microstomus kitt (Walbaum)

Atlantic halibut, Hippoglossus hippoglossus L., eat larger satiation meals (mean 11.7% body weight) than lemon sole, Microstomus kitt (Walbaum), (2.6% body weight). Total gut clearance time was about 120 h for halibut and 72 h for lemon sole. There are marked differences in feeding behaviour between the two species; halibut feed in midwater and require several body lengths of approach swimming before taking large items of food, while lemon sole eat only off the bottom. In shared tanks, no aggressive interaction was observed. A duoculture system holding small numbers of lemon sole with the more valuable halibut is recommended as a means of minimizing food waste and tank fouling. Oxygen uptakes of 0.07-0.11 ml O₂ g fish wt⁻¹ h⁻¹ (depending on nutritional state) were recorded for the two species. Ammonia nitrogen outputs were also similar. Starved halibut excreted 2.32 μg N g⁻¹ h⁻¹, fed animals 5.08 μg N g⁻¹ h⁻¹. The corresponding values for lemon sole were 3.26 μg N g⁻¹ h⁻¹ and 6.37 μg N g⁻¹ h⁻¹, respectively.     

Cage aquaculture in Neotropical waters promotes attraction and aggregation of fish

The influence of cage aquaculture on the attraction and aggregation of wild fish was evaluated with an experimental tilapia farming structure. The structure was installed in the Corvo River, Rosana Reservoir, Paranapanema River basin, for 140 days. Samples were taken before and after farming began. Gillnets on the surface and near the bottom at different distances from the cages (0, 100 and 400 m) were used for fish sampling. The effects of the food supply at two protein levels were also analysed: Phase 1 = 32% PB and Phase 2 = 28% PB. Changes in species richness and abundance were observed, with the number of individuals and the fish biomass increasing significantly just after the farming began. Some species, such as Iheringichthys labrosus, presented increased abundance near the cages, while others, such as Plagioscion squamosissimus, were more abundant far from the cages. Auchenipterus osteomystax was the most abundant species during the experiment, especially when the protein content of the pellets was higher. It was demonstrated that farming tilapia in cages profoundly altered the abundance and composition of the wild ichthyofauna, suggesting the need to propose effective regulations for such activities, including fisheries restrictions in farmed areas or even the prohibition of cage farming.     

Influence of hunger level and food availability on the spatial distribution of Atlantic salmon, Salmo salar L., in sea cages

Abstract. The spatial distribution of Atlantic salmon, Salmo salar L., in sea cages was observed by echo integration, which measured fish density at seven in depth intervals. At start of feeding the fish swam towards the surface and into the centre of the cage with a subsequent movement downwards and towards the periphery as hunger was reduced. These changes were more rapid at high than at low feeding intensities. The downward migration during feeding was primarily observed as a reduction in fish density in the 0–1 m depth layer and an increase in the 2–3 m depth layer. For a given feeding intensity, the change in fish density in these depth layers was largely explained by time from the start of feeding and initial hunger level, measured as food intake to satiation. The feeding regime also influenced vertical distribution outside feeding periods. Fish that were fed at low intensity swam generally closer to the surface, and this tendency was even stronger when a restricted food ration kept hunger level constantly high. While fish density peaked at a single depth interval at full ration, a bimodal vertical distribution was observed at restricted ration, suggesting that different subgroups of fish had different feeding motivations. The results suggest that the vertical distribution of salmon in sea cages is based on a trade-off between attraction to food and avoidance of the surface. This tendency has been exploited in a new method of demand feeding in commercial farming of Atlantic salmon.     

The effect of demand feeding on swimming speed and feeding responses in Atlantic salmon Salmo salar L., gilthead sea bream Sparus aurata L. and European sea bass Dicentrarchus labrax L. in sea cages

Abstract Using underwater cameras, data were collected on the feeding behaviour and swimming speeds of Atlantic salmon Salmo salar L., gilthead sea bream Sparus aurata L. and European sea bass Dicentrarchus labrax L. in sea cages. Comparisons were made between the behaviours of fish fed on demand using interactive feedback systems and those of fish fed under the standard feeding practice of each farm (control). In all three species, swimming speeds were similar before feeding , but they were significantly higher in the control regimes during feeding. When fed on demand, sea bass had reduced swimming speed just before and during feeding compared with that observed during the non‐feeding periods. Higher proportions of feeding fish were observed in the control regime cages than in fish fed on demand for all three species, indicating a greater feeding intensity during meals in the control regimes. This was further supported by observations of an increase in the density of sea bass in the upper water in the control cages during feeding. The results suggest decreased levels of competition between the on demand‐fed fish during feeding, which might be hypothesized to lead to improved growth and production efficiency in aquaculture.     

Histopathology of culture‐associated skin erosions and papillary hyperplasia of Atlantic halibut,Hippoglossus hippoglossus (L.)

Atlantic halibut, Hippoglossus hippoglossus (L.), that were cultured in tanks with a smooth bottom (gel‐coated fibreglass) substrate developed papillary hyperplasia and skin erosions on the blind (ventral) side. No viruses, bacteria or parasites were observed in any sections of affected skin. Comparison of microscopic pathology with that of skin from normal, wild‐caught halibut showed severe epidermal proliferation with foci of severe mucous cell hyperplasia. Both epidermal thickness and mucous cell density were significantly greater in fish held on a smooth substrate compared to skin of healthy fish. Spongiosis was present, especially at the base of the papillary, hyperplastic epidermis, and there was a chronic inflammatory infiltrate in the scale pockets composed of lymphocytes, histiocytes and erythrocytes. Skin erosions had various degrees of epidermal loss, in some cases to the basement membrane. A predisposing factor for the epidermal sloughing may have been related to the spongiosis, and the vacuolated, degenerated basal cells. When affected halibut were cultured for an additional 28, 62 or 97 days on a sand substrate, which is conducive to skin lesion healing, there was no apparent change in epidermal thickness over time. However, mucous cell density significantly increased from day 0 to 97 during the healing process.     

双层网底鲆鲽网箱耐流特性的数值模拟

双层网底鲆鲽网箱的网底结构在水流作用下会发生倾斜与转动。为确保网底结构的安全,需对其耐流特性进行动力分析。为此,根据有限元法建立了流场中双层网底网箱受力的数学模型,通过计算机数值模拟对双层网底的最大位移与倾角进行研究,并将双层网底的计算结果与单层网底进行对比分析。模拟结果显示,随着流速的增大,上层网底与下层网底的倾角逐渐增加,并且两层网底的倾斜方向恰好相反。研究发现,当实际海区流速超过93 cm/s时,双层网底网箱的上、下两层网底会发生接触碰撞,从而影响网底的稳定。此外,双层网底网箱的下层网底位移要大于单层网底网箱,但其倾角却小于后者,这可能与双层网底网箱的上层网底设计有关。     

Environmental effects of the anti-sea lice (Copepoda: Caligidae) therapeutant emamectin benzoate under commercial use conditions in the marine environment

Sea lice infestation can pose a particular problem to intensive cage aquaculture of salmonids. It is most often treated by therapeutants added to the water or incorporated into fish feed. This study investigated the environmental effects of one such in-feed treatment, emamectin benzoate, under commercial use conditions. Atlantic salmon were fed the commercial preparation of emamectin benzoate at a production fish farm on the west coast of Scotland. Sediment dwelling fauna, large mobile fauna and sentinel organisms were monitored for potential impacts over a 1 year post-treatment period (23 September 1997 to 23 September 1998). Additionally, sediment and water samples, transplanted blue mussels and captured large fauna were analysed for accumulated emamectin benzoate and its desmethylamino metabolite to investigate the long term environmental fate of emamectin benzoate.

Results from analysis of sediments suggested that limited deposition of emamectin benzoate took place during and up to 1 week post-treatment, and may have continued up to 4 months of post-treatment. This was consistent with the release of the active ingredient from fish excretion and defecation after treatment. Quantifiable amounts of emamectin benzoate were found 10 m from the cages 12 months after treatment. However, clear reduction in overall sediment concentrations indicated that the deposited emamectin was degrading over time. Emamectin benzoate was not detected in water samples during the field trial. Quantifiable concentrations of emamectin benzoate were found in blue mussels deployed up to 100 m from the treatment cages at 1 week post treatment, but found only at 10 m from the cages at 1 month post-treatment. This suggests that while mussels were actively accumulating emamectin benzoate immediately after treatment by 1 month this had largely been depurated.

Macrobenthic faunal analysis indicated that there was no evidence that the occurrence of emamectin benzoate, or its desmethylamino metabolite, in sediments around fish farm cages after treatment had any toxic impacts on organisms in either water column or sediments.     

Response of Israeli carp, Cyprinus carpio L., to lysine supplementation of a practical ration at varying conditions of fish size, temperature, density and ration size

Abstract. Four feeding trials with Israeli carp, Cyprinus carpio L., were performed in cages or in ponds in order to investigate responses to lysine supplementation of low protein carp feeds under different practical conditions. In each of the trials one of the basic conditions was different: fish size—small (80–125g) or large (560g); temperature—22°C or 26°C; density—cages or ponds. In each trial 2–3 ration sizes × 2–3 lysine levels were tested. A basal diet of 25% protein and 1·35% lysine served for all the trials.
At low feeding levels, no responses to lysine supplements were found either at 22 ± 2°C or at 26 ± 2°C (0600 h) for all fish sizes. At higher feeding levels, at both temperatures, 0·5% lysine-HCl supplements to 1·7% total lysine yielded significant growth increases. Further supplements to 2·1% lysine (=8·4% of the protein) brought an additional response only from small fish of 90g in cages at the highest ration and temperature. In ponds at 26°C, the effects on small fish of 80g were smaller, probably due to available natural food. The reduction in lysine retention suggested that 1·7% lysine might have been adequate even at optimal conditions in ponds.