The effect of density on sea bass (Dicentrarchus labrax) performance in a tank-based recirculating system

Sea bass (Dicentrarchus labrax) (135 ± 4 g) were reared under tank-based recirculating aquaculture system for a 63-day period at four densities: 10, 40, 70, 100 kg m^?3. Fish performance, stress indicators (plasma cortisol, proteonemia plus other blood parameters—Na⁺, K⁺, glucose, pH, total CO₂^?) and water quality were monitored. At the end of the 63-day period, resistance to infection was also studied by a nodavirus challenge. A 25-day test was performed on fish from two extreme densities (10 and 100 kg m³) and one intermediate density (40 kg m³).With regards to the different density treatments, there was no significant difference between the daily feed intake (DFI) and the specific growth rate (SGR) up to a density of 70 kg m^?3. No significant difference was found between treatments concerning the feed conversion ratio (FCR) and the mortality rate. No density effect was observed on the fish stress level (plasma cortisol) or on sensitivity to the nodavirus challenge. Under these experimental rearing conditions, the density above 70 kg m^?3 has an impact on growth performance (DFI and SGR) indicators and also some blood parameters (CO₂) at the highest density tested (100 kg m^?3).This study suggests that a density up to 70 kg m^?3 has no influence on sea bass performance and welfare. At 100 kg m^?3, average specific growth rate was decreased by 14% without welfare deterioration according to the welfare indicators monitored.     

Effects of stocking density of freshwater prawn Macrobrachium rosenbergii and addition of different levels of tilapia Oreochromis niloticus on production in C/N controlled periphyton based system

An on-station trial was conducted to evaluate the effect of stocking density of freshwater prawn and addition of different levels of tilapia on production in carbon/nitrogen (C/N) controlled periphyton based system. The experiment had a 2 × 3 factorial design, in which two levels of prawn stocking density (2 and 3 juveniles m^? 2) were investigated in 40 m² earthen ponds with three levels of tilapia density (0, 0.5 and 1 juveniles m^? 2). A locally formulated and prepared feed containing 30% crude protein with C/N ratio close to 10 was applied considering the body weight of prawn only. Additionally, tapioca starch was applied to the water column in all ponds to increase C/N ratio from 10 (as in feed) to 20. Increasing stocking density of tilapia decreased the chlorophyll a concentration in water and total nitrogen in sediment, and increased the bottom dissolved oxygen. The concentrations of inorganic nitrogenous species (NH₃–N, NO₂–N and NO₃–N) were low due to maintaining a high C/N ratio (20) in all treatment ponds. Increasing prawn density decreased periphyton biomass (dry matter, ash free dry matter, chlorophyll a) by 3–6% whereas tilapia produced a much stronger effect. Increasing stocking density of freshwater prawn increased the total heterotrophic bacterial (THB) load of water and sediment whereas tilapia addition decreased the THB load of periphyton. Both increasing densities of prawn and tilapia increased the value of FCR. Increasing prawn density increased gross and net prawn production (independent of tilapia density). Adding 0.5 tilapia m^? 2 on average reduced prawn production by 12–13%, and tilapia addition at 1 individual m^? 2 produced a further 5% reduction (independent of prawn density). The net yield of tilapia was similar between 0.5 and 1 tilapia m^? 2 treatments and increased by 8.5% with increasing stocking density of prawn. The combined net yield increased significantly with increasing stocking density of prawn and tilapia addition. The significantly highest benefit cost ratio (BCR) was observed in 0.5 tilapia m^? 2 treatment but freshwater prawn density had no effect on it. Therefore, both stocking densities (2 and 3 juveniles m^? 2) of prawn with the addition of 0.5 tilapia m^? 2 resulted in higher fish production, good environmental condition and economic return and hence, polyculture of prawn and tilapia in C/N controlled periphyton based system is a promising options for ecological and sustainable aquaculture.     

Management of stocking density,pond size,starting time of aeration,and duration of cultivation for intensive commercial production of shrimp Litopenaeus vannamei

A dynamic stock model was used for quantification of shrimp production and analysis of alternative management schemes of stocking density, pond size, starting time of aeration, and duration of cultivation for intensive commercial production of the shrimp Litopenaeus vannamei. Databases from Mexican farms were used to calibrate the model. Multiple linear regression models were employed to establish relationships between parameters of the stock model and the management variables. Water quality variables (dissolved oxygen, temperature, and salinity) were complementarily analyzed. The final weight of shrimp was directly related to duration of cultivation and dissolved oxygen, and inversely related to stocking density, pond size, and salinity. There were inverse relationships between the growth coefficient and temperature and dissolved oxygen and between mortality rate and temperature. Dissolved oxygen was significantly related to starting time of aeration. Simple linear regression and an equivalence test indicated that biomass at harvest (after 13 weeks in winter, and 20 weeks in summer) was adequately predicted by using the stock model and the multiple regression models. The highest production (winter, 6900 kg ha⁻¹; summer, 12,600 kg ha⁻¹) were predicted using 60 postlarvae m⁻², small ponds (2 ha), and starting aeration at the first week of cultivation; while the lowest yields (winter, 2600 kg ha⁻¹; summer, 6000 kg ha⁻¹) were obtained using 40 postlarvae m⁻², large ponds (8 ha), and delaying the start of aeration until the fifth week of cultivation. The lowest production was 38% (winter) and 48% (summer) of the highest yield. Using small ponds could be particularly important during winter cycles to increase production, while stocking density and starting time of aeration contributed less. In contrast, pond size played a minor role during summer cycles and stocking density was the most sensitive variable.     

Estimation of mercury uptake efficiency and the development of feed input models for the evaluation of baitfish regimes in determining mercury concentration of farmed southern bluefin tuna (Thunnus maccoyii)

A model is presented for the prediction of mercury (Hg) concentrations in the edible tissues of farmed southern bluefin tuna, Thunnus maccoyii (SBT) during commercial culture. The predictive model was developed using the initial Hg concentration of wild-caught SBT (mg kg^? 1), Hg concentration of feed (mg kg^? 1), SBT feeding rate (kg kg^? 1 day^? 1), SBT tissue growth rate (kg day^? 1) and least squares minimisation estimation of Hg uptake efficiency, η. Model development and validation was based on experimental data collected from commercially cultured SBT which are farmed in in-sea pontoons (sea-pontoons). Model predictions indicate that over a typical farming season SBT from each of three commercially operated sea-pontoons experienced a 0.1 mg kg^? 1, 0.14 mg kg^? 1 and > 0.2 mg kg^? 1 reduction in the Hg concentration of muscular tissues respectively. This is the first study to attempt to estimate Hg uptake efficiency in a tuna species. Estimation of Hg uptake efficiency and development of a working model for prediction of Hg concentration in SBT under varying culture diets, represent the first steps towards taking the guesswork out of managing Hg residues in cultured tuna.     

Experimental investigation on the transport of different fish species in a jet fish pump

A jet fish pump with a throat of ø60 mm was designed to study its performance in the transport of different fish species and the physiological changes in fish thereafter. Experiments were conducted to investigate the fish transport rate and energy required to transport each ton of fish when transporting Carassius auratus, commonly known as the Chinese goldfish, Megalobrama amblycephala, or Wuchang bream, and Ctenopharyngodon idella, the grass carp. Fish were examined for external injuries as well as for several important enzymes and hormones which are indicators of tissue injury and stress. The results showed that the transport rate for all three species of fish rose dramatically with an increase in the primary stream rate. In this experiment, the transport rates of C. auratus, M. amblycephala and C. idella reached 2357 ± 37.2 kg ∙ h⁻¹, 2888 ± 41.6 kg ∙ h⁻¹, and 2060 ± 40.2 kg ∙ h⁻¹, respectively. However, both injury rate and energy required to transport each ton of fish increased no matter whether the primary stream rate was too low or too high. Considering both transport rate and injury rate, the mean primary stream rate of 80 m³ ∙ h⁻¹ was determined to be the optimal operating condition in this experiment. Fish were stressed and most likely some of their organs were damaged. However, most physiological indexes almost fully recovered after several hours.     

Water quality and rainbow trout performance in a Danish Model Farm recirculating system: Comparison with a flow through system

The objective was to compare water quality and fish growth and mortality in a pilot scale recirculating system (RS) and a control tank in flow through system (FTS). The RS was designed after the Danish Model Trout Farm and operated with a make up water renewal rate of 9 m³ kg^-1 of fish produced. RS water quality did not decrease significantly with water flow rate decrease in the RS. During the experiment, the RS water treatment system presented solids removal efficiency of 59.6 ± 27.7% d⁻¹, ammonia oxidation of 45 ± 32 g m⁻³ d⁻¹, oxygenation yield of 392 ± 132 g of O₂ kWh⁻¹ and CO₂ degassing of 23.3 ± 11.9% pass⁻¹. In the RS, nitrite concentration was 0.15 ± 0.07 mg l⁻¹, close to the toxicity threshold; a N₂ supersaturation phenomenon was measured, probably due to the air injection depth. The biofilter and sedimentation area management has to be improved to avoid organic matter decomposition and release of dissolved elements. Even if no N₂ over-saturation apparent effect on fish performance and aspect were detected, the airlift depth has to be modified in the case of industrial development of the RS. Some improvements of the water treatment system, especially on the airlift and sedimentation area, are suggested.Concerning fish growth, no significant differences were observed between the RS and the FTS. No pathologies were detected and cumulative mortality rates (0.1%) were similar to the farm's usual data. There were no significant effects of water flow rate decrease in the RS on fish performance and energy savings were recorded to be 0.7 kWh kg⁻¹ of fish produced between RS₁ and RS₂. The global energy cost of the RS was 3.56 kWh kg⁻¹ of fish produced (0.107 € kg⁻¹ of fish produced). Even if the energy consumption of the water treatment system can be improved, the results confirm that recirculating system can be used for industrial trout on growing, without fish performance deterioration.     

A novel approach for ammonia removal from fresh-water recirculated aquaculture systems,comprising ion exchange and electrochemical regeneration

A new physico-chemical process for ammonia removal from fresh-water recirculated aquaculture systems (RASs) is introduced. The method is based on separating NH₄⁺ from RAS water through an ion-exchange resin, which is subsequently regenerated by simultaneous chemical desorption and indirect electrochemical ammonia oxidation. Approach advantages include (1) only slight temperature dependence and no dependence on bacterial predators and chemical toxins; (2) no startup period is required and the system can be switched on and off at will; and (3) the fish are grown in much lower bacterial concentration, making the potential for both disease and off-flavor, lower. A small pilot scale RAS was operated for 51 d for proving the concept. The system was stocked by 105 tilapia fish (initial weight 35.8 g). The fish, which were maintained at high TAN (total ammonia nitrogen) concentrations (10–23 mgN L⁻¹) and fish density of up to 20 kg m⁻³, grew at a rate identical to their established growth potential. NH_3(aq) concentrations in the fish tank were maintained lower than the assumed toxicity threshold (0.1 mgN L⁻¹) by operating the pond water at low pH (6.5–6.7). The low pH resulted in efficient CO₂ air stripping, and low resultant CO_2(aq) concentrations (<7 mg L⁻¹). Due to efficient solids removal, no nitrification was observed in the fish tank and measured nitrite and nitrate concentrations were very low. The system was operated successfully, first at 10% and then at 5% daily makeup water exchange rate. The normalized operational costs, calculated based on data derived from the pilot operation, amounted to 28.7 $ cent per kg fish feed. The volume of the proposed process was calculated to be ∼13 times smaller than that of a typical RAS biofilter. The results show the process to be highly feasible from both the operational and economical standpoints.     

Effects of stocking density on haematological parameters,growth and fin erosion of great sturgeon (Huso huso) juveniles

The influence of stocking density (1, 2, 4, 6 and 8 kg m^?2) was investigated on haematological parameters, growth and fin erosion of great sturgeon (Huso huso) juveniles for a period of 8 weeks. The mean weight of fish at the start of trial was 93.13±1.04 g. After 8 weeks of rearing, the mean weight was 362.4, 319.7, 267, 242.1 and 211.1 in densities 1–8 kg m^?2 respectively. The results of this study showed that growth parameters, including condition factor, weight, weight gain, feed conversion ratio, specific growth rate and body weight increase, had a statistically significant difference among treatments (P<0.05). A significant difference (P<0.05) was observed in haematocrit, but the other haematological parameters, including red blood cells, white blood cells (WBC), haemoglobin concentration, mean corpuscular haemoglobin, mean corpuscular volume, mean corpuscular haemoglobin concentration and differential WBC count, showed no significant effect with stocking density (P>0.05). At the end of the experiment, stocking density had no significant effect on plasma cortisol and glucose concentration. The fin length (dorsal, anal, ventral, pectoral and caudal) of fish was measured to calculate the fin index. According to this index, dorsal, anal, ventral and pectoral fins showed no significant difference among treatments (P>0.05), but the erosion of the caudal fin was significantly different between fish held on 6 and 8 kg m^?2 (P<0.05). These results showed that rearing density has a major effect on the growth indices of H. huso. Unlike many other fish, great sturgeon exhibited lower stress responses to high stocking density. This indicates that they are more tolerable to rearing conditions in high stocking densities. With respect to the various effects that density causes on growth, fin erosion and physiological and haematological parameters, better understanding of these phenomena considering different levels of density could have a beneficial impact on many rearing steps of this species.     

Aquacultural System Management Tool (AQUASMAT) I: Model development

Most developed aquacultural models are designed for foreign species and environments and hence the need to develop a model for African farmed fish. This paper describes the development of an Aquacultural System Management Tool (AQUASMAT) for predicting tank systems for culturing African catfish (Clarias gariepinus). The model development involved formulation of theoretical relationships for intensive tank-based fish culture from existing models and development of program code with Microsoft^® Visual C# (C-sharp). The model was designed to predict the effect of different management operations on fish yield, identify and quantify the cause, effect and relationships between water quality parameters, and suggest remedial actions for impaired systems. It also predicts economic viability of the production system based on cost input used in the system and track the fate of many water quality parameters which are not readily measured. The developed model was calibrated, validated and applied to ascertain its suitability. The model calibration results showed a close trend between the predicted and observed data, indicating a reasonable performance and adequacy of system representation. Regression analysis on the validated results indicated a strong correlation between predicted and observed data for TAN, temperature, NO₃ and fish weight. Model adequacy results were within the recommended range, with relative bias (rB) of 0.014, −0.159, 0.039, −0.104 and F-test of 0.740, 0.877, 0.887 and 0.736 for temperature, DO, TAN and fish weight, respectively. Model sensitivity analysis showed that the model was very sensitive to parameters such as temperature, pond size, feed and stocking density, hence accurate estimation of these parameters is recommended for optimal performance of the model. Model experimentation results showed DO and TAN were within tolerable water quality limits only for stocking densities of 7 fish/m², 14 fish/m² and 21 fish/m² and predicted profit in Nigerian currency, Naira (

) of

1100:00,

1681:00,

1575:00,

820:00 for 7 fish/m², 14 fish/m², 21 fish/m² and 28 fish/m², respectively, and a loss of

1501:00 for 35 fish/m² for the model scenarios.     

Use of avoidance response by rainbow trout to carbon dioxide for fish self-transfer between tanks

Convenient, economical, and reduced labor fish harvest and transfer systems are required to realize operating cost savings that can be achieved with the use of much larger and deeper circular culture tanks. To achieve these goals, we developed a new technology for transferring fish based on their avoidance behavior to elevated concentrations of dissolved carbon dioxide (CO₂). We observed this behavioral response during controlled, replicated experiments that showed dissolved CO₂ concentrations of 60–120 mg/L induced rainbow trout (Oncorhynchus mykiss) to swim out of their 11 m³ “growout” tank, through a transfer pipe carrying a flow with ≤23 mg/L dissolved CO₂, into a second 11 m³ “harvest” tank. The research was conducted using separate groups of rainbow trout held at commercially relevant densities (40–60 kg/m³). The average weight of fish ranged from 0.15 to 1.3 kg during the various trials. In all trials that used a constant flow of low CO₂ water (≤23 mg/L) entering the growout tank from the harvest tank, approximately 80–90% of the fish swam from the growout tank, through the transfer pipe, and into the harvest tank after the CO₂ concentration in the growout tank had exceeded 60 mg/L. The fish that remained in the growout tank stayed within the area of relatively low CO₂ water at the entrance of the transfer pipe. However, the rate of fish transfer from the growout tank to the harvest tank was more than doubled when the diameter of the transfer pipe was increased from 203 to 406 mm. To consistently achieve fish transfer efficiencies of 99%, water flow rate through the fish transfer pipe had to be reduced to 10–20% of the original flow just before the conclusion of each trial. Reducing the flow of relatively low CO₂ water near the end of each fish transfer event, restricted the zone of relatively low CO₂ water about the entrance of the fish transfer pipe, and provided the stimulus for all but a few remaining fish to swim out of the growout tank. Results indicate that the CO₂ avoidance technique can provide a convenient, efficient, more economical, and reduced labor approach for fish transfer, especially in applications using large and well mixed circular culture tanks.     

Evaluating the chronic effects of nitrate on the health and performance of post-smolt Atlantic salmon Salmo salar in freshwater recirculation aquaculture systems

Commercial production of Atlantic salmon smolts, post-smolts, and market-size fish using land-based recirculation aquaculture systems (RAS) is expanding. RAS generally provide a nutrient-rich environment in which nitrate accumulates as an end-product of nitrification. An 8-month study was conducted to compare the long-term effects of “high” (99 ± 1 mg/L NO₃-N) versus “low” nitrate-nitrogen (10.0 ± 0.3 mg/L NO₃-N) on the health and performance of post-smolt Atlantic salmon cultured in replicate freshwater RAS. Equal numbers of salmon with an initial mean weight of 102 ± 1 g were stocked into six 9.5 m³ RAS. Three RAS were maintained with high NO₃-N via continuous dosing of sodium nitrate and three RAS were maintained with low NO₃-N resulting solely from nitrification. An average daily water exchange rate equivalent to 60% of the system volume limited the accumulation of water quality parameters other than nitrate. Atlantic salmon performance metrics (e.g. weight, length, condition factor, thermal growth coefficient, and feed conversion ratio) were not affected by 100 mg/L NO₃-N and cumulative survival was >99% for both treatments. No important differences were noted between treatments for whole blood gas, plasma chemistry, tissue histopathology, or fin quality parameters suggesting that fish health was unaffected by nitrate concentration. Abnormal swimming behaviors indicative of stress or reduced welfare were not observed. This research suggests that nitrate-nitrogen concentrations ≤ 100 mg/L do not affect post-smolt Atlantic salmon health or performance under the described conditions.     

Bio-flocs technology application in over-wintering of tilapia

A 50-day experiment was conducted to investigate the effectiveness of the bio-flocs technology for maintaining good water quality in over-wintering ponds for tilapia hybrid fingerlings (Oreochromis niloticus × Oreochromis aureus). To preserve adequate water temperatures in the ponds, they were covered with polyethylene sheets and the water exchange rate was minimized to increase pond water temperature. To avoid water quality deterioration, starch was added to the ponds to stimulate the formation of bio-flocs. Temperature in the covered ponds could easily be controlled and was 0.4–4.9 °C higher than the influent water. Adjusting the C/N ratio in the ponds by adding starch or increasing the amount of carbohydrates added through the feed limited the presence of inorganic nitrogen species when the C/N was about 20, even at high stocking densities of 20 kg/m³ at harvest. Fish survival levels were excellent, being 97 ± 6% for 100 g fish and 80 ± 4% for 50 g fish. Moreover, at harvest the condition of the fish was good in all ponds with a fish condition factor of 2.1–2.3. Overall, these findings can help to overcome over-wintering problems, particularly mass mortality of fish due to low temperatures in the ponds.     

Effect of water recirculation on seawater quality and production of scallop (Pecten maximus) larvae

Scallop larval production systems in Norway have changed from the use of batch to continuous flow through systems (FTS) during the last decade. Energy use to heat water in both larval and spat nurseries is considerable. Two experiments (June 2010 and February 2011) using water recirculation technology (RAS) were performed in large scale systems (3500 L larval tanks) supplied with continuous addition of algal feed, and 20% renewal of seawater.In the RAS a gradual increase in CO₂, decrease in pH and dissolved oxygen was observed over time. This was most obvious during experiment two, when the total organic carbon content increased in both FTS and RAS. The total bacterial number was lower and more stable in FTS than in the RAS. The variations in seawater quality parameters were smaller during the first experiment compared to the second, when values of oxygen saturation were reduced to <70%, pH was 7.8 and NO₃⁻ reached 5 mg L⁻¹. Even though these changes would seem less beneficial for survival and growth of scallop larvae, results showed that the survival at the end of the larval stage was higher in the FTS, but the yield of competent larvae ready for settlement was not significant different (p > 0.05) due to large variations between tanks. The CV% was 28.9% in FTS, while it was 49.9% in RAS. In FTS the mean yield was 40.2%, while it was 26.5% of initial number of larvae in RAS. Large variations in survival and yield were found between the larval tanks as well as gradual reduction in pH and oxygen in RAS tanks. The results indicate that there is a large potential for 80% reduction in water use by utilizing recirculation technology.     

Interaction of dietary energy levels and culture density on growth performance and metabolic and oxidative status of rainbow trout (Oncorhynchus mykiss)

Rainbow trout (100 g initial weight) were subjected to the combined effect of two culture densities (15 and 40 kg m⁻³, D15 and D40, respectively) and two dietary energy levels (22 and 27 MJ kg⁻¹ E22 and E27, respectively) during a 75-days experimental period. At the end of the experiment, the growth rate as well as the metabolic and oxidative status of liver and muscle of fish were studied.The results showed that combination of culture density and dietaryenergy level negatively affected growth, cholesterol and LDL plasma levels and oxidative stress in muscle. Higher culture density negatively affected the values of total protein, triglycerides, and HDL in plasma, values of hepatic and muscular metabolic activities pyruvate kinase (PK), citrate synthase (CS), and hydroxiacil-CoA dehydrogenase (HOAD); glutamate pyruvate transaminase (GPT) and glutamate oxaloacetate transaminase (GOT) activities in plasma, liver, and muscle; glucose 6P dehydrogenase (G6PDH) activity in muscle; and oxidative stress in liver.High energy intake, adversely affected the hepatic activity of G6PDH, HOAD, GPT and oxidative stress in muscle.Consequently our results indicate that a combination of high culture density and a high level of dietary energy (27 MJ kg⁻¹ in diet) exert a negative impact on the physiology and consequently on the welfare of the farmed fish.     

The efficiency of three fry trawls for sampling the freshwater pelagic fry community

Avoidance reactions of young-of-the-year fish assemblages were investigated in the offshore zone of three reservoirs in the Czech Republic during late summer. Pikeperch (Stizostedion lucioperca) strongly dominated in the Lipno Reservoir in 2003, bream (Abramis brama) and bleak (Alburnus alburnus) were the most abundant species in the Slapy Reservoir in 2004 and roach (Rutilus rutilus) and bleak dominated in the Želivka Reservoir in 2004 and 2005. Densities of fry ranged between 1.09 ind./100 m³ in the Lipno Reservoir and 2.95 ind./100 m³ in the Slapy Reservoir. In each reservoir, three trawl nets of different widths (dimensions 1.5 m × 3 m, 3 m × 3 m, 6 m × 3 m) were used in the pelagic area at night. For each trawl the estimated fish density was determined as the catch per 100 m³ of water and was compared between all three trawls. The fish length–frequency distribution was also compared between all the trawls. Day catches were much lower compared with those taken at night. Adult fish showed very clear avoidance of fry trawls. At night, no important differences in estimated fry density, obtained by these trawls, were observed in any locality for any fish species, nor in the length distribution of important species between trawls. According to these results, the avoidance reactions of fry in the late summer (August, September), at night, are unimportant. At this time of year, nighttime pelagic trawling appears to be an effective method for quantitative fry sampling. We recommend the 3 m × 3 m trawl for quantitative night sampling of the fry community as a good compromise between assured efficiency and relatively easy handling.     

Routine oxygen consumption rates of california halibut (Paralichthys californicus) juveniles under farm-like conditions

Fish oxygen requirement is a fundamental variable of aquaculture system design and management, as it is the basis for determining water flow rates for sustaining stock. A study on oxygen consumption of California halibut (Paralichthys californicus) between 3.2 and 165.6 g was conducted in small raceways (2.41 m long, 0.28 m wide, and 0.22 m high; operational water depth between 0.05 and 0.10 m with a quiescent zone 19 cm long in the effluent section) working as open respirometers in a recirculating system under farm-like conditions. The fish were fed commercial dry pelleted feeds at a ratio of ～0.70–3.00% of body weight (BW) and stocked at densities between 94% and 316% percent coverage area (PCA). Oxygen consumption rates were determined by mass balance calculations. The mean and maximum oxygen consumption rates (g O₂/kg fish/day) for juvenile California halibut under the conditions tested can be expressed by M_day = 15.077W^?0.2452 and M_day = 17.266W^?0.2033, respectively, where W is fish weight in grams. The determination of oxygen consumption by California halibut in farm-like conditions provides valuable information on the oxygen requirement of these fish in an aquacultural setting. This information can be used for designing and sizing a rearing facility for the intensive culture of California halibut.     

Effects of two temperatures on the oxygen consumption rates of Seriolella violacea (palm fish) juveniles under rearing conditions

Oxygen consumption rates (mg O₂/kg fish/min; OC) of juvenile palm fish (average weight 420 g) were determined for temperatures of 14 and 18 °C. Three replicates of two tanks rearing fish at a density of 24 kg/m³ were used to measure OC at 34 ppt working as open respirometers in a recirculating system under farm-like conditions. The fish were fed commercial dry pelleted feeds at a ratio of 1% of total biomass. Oxygen consumption rates were determined by mass balance calculations. The OC increased from 1.6 to 2.4 g O₂/kg fish/day as temperature increased from 14 to 18 °C. The determination of oxygen consumption by palm fish in farm-like conditions provides valuable information on the oxygen requirement of these fish in an aquacultural setting. This bioengineering information can be used for designing and sizing a rearing facility for the intensive culture of palm fish.     

Age and growth estimates of the sharptail mola,Masturus lanceolatus,in waters of eastern Taiwan

The sharptail mola, Masturus lanceolatus, is one of the largest teleost fishes in the world, and can be found in warm temperate and tropical regions worldwide. The increase of sharptail mola catch in the eastern Taiwan in recent years stimulated a concern that increasing exploitation of this species might lead to a decline of the stock. However, biological information of this species is very limited. Hence, this study provides the first information on age and growth of this species in the waters off eastern Taiwan based on 265 specimens (105 females and 160 males) collected from January 2003 to November 2006 at the Nanfanao and Hualien fish markets, eastern Taiwan. The relationships between whole weight (W) and standard length were expressed as: W = 9.98 × 10^?4 SL^2.45 (n = 105, p < 0.01) for females, and W = 3.33 × 10^?4 SL^2.68 (n = 160, p < 0.01) for males. Based on the MIR analysis, growth band pairs (including translucent and opaque bands) in vertebrae formed once a year and were counted up to 23 and 16 for females and males, respectively. Three growth functions, the von Bertalanffy (VBGF), Robertson, and Gompertz, were used to model the observed length at age data. The VBGF had the best fit and predicted an asymptotic length (L_∞) = 262.5 cm SL, growth coefficient (k) = 0.046 yr^?1, age at zero length (t₀) = ?3.350 yr (n = 80, p < 0.01) for females, and L_∞ = 231.0 cm SL, k = 0.059 yr^?1, t₀ = ?1.852 yr (n = 135, p < 0.01) for males. The longevities were estimated to be 105 and 82 yr based on the VBGF for females and males, respectively.     

Design and evaluate a drum screen filter driven by undershot waterwheel for aquaculture recirculating systems

Micro-screen rotating drum filters are an alternative to sand filtration especially when excessive waste water is a concern. The filtering process of drum screen filters is very simple, yet very efficient and reliable due to their overall design and operation. Drum filters are designed with few moving parts to ensure a long life with low operating/maintenance costs.Micro-screening essentially captures particles on a screen fabric while letting the water pass. This paper describes a design of two an industrial-scale drum screen filters driven by undershot wheel and its performance installed in recirculating aquaculture system culturing tilapia at El-Nenaeia fish farm. These filters are consisted of a woven metal mesh of 100 μm. The design criteria for solids loading rate in the influent water is 10 kg m⁻² min⁻¹.The results indicate that the design parameters of the filter such as surface are and rotation speed were affected by the water flow rate, where the surface area and drum speed ranged from 1.58 to 27.87 m², and 1.05 to 8.40, respectively. The results also indicated that the efficiency of filter decreased during the first two months compared to the last two months of fish growth period, with an average 34.22 ± 8.85% during the first 60 days and an average 52.41 ± 16.77% during the last period. Using water wheels for driving the screen filter is very important in saving energy, where the filter with such dimensions needs 1.0 hp for driving it, which represents 18.0 kW daily.     

Effects of stocking density and feeding duration in cage‐cum‐pond‐integrated system on growth performance,water quality and economic benefits of Labeo victorianus (Boulenger 1901) culture

We evaluated the effect of varying cage stocking density (60, 90 and 120 fish m^?3) and feeding duration (10, 30 and 60 min) in a cage‐cum‐pond‐integrated system on growth performance, water quality and economic benefits in Labeo victorianus culture. Interactions between stocking density and feeding duration significantly (P < 0.05) affected the fish growth performance and yields in the cages‐cum‐pond system. Stocking density of 60 fish m^?3 resulted in the highest growth in cages and in ponds regardless of the feeding duration, but produced lower yields than at stocking density 90 fish m^?3_. The lowest Apparent Food Conversion Ratio (AFCR) in cages occurred at stocking density of 60 fish m^?3 and feeding duration of 30 min. Growth performance in the open ponds declined with increased feeding duration of the caged fish. Survival in cages and in the open ponds decreased with increased cage density, but was not affected by feeding duration. Low dissolved oxygen were recorded, at stocking density of 120 fish m^?3, the lowest DO occurred when feeding of caged fish lasted 60 min. Growth performance, water quality and economic benefits in Labeo victorianus culture positively respond to interaction between stocking density and feeding durations.