Growth of Daphnia magna on urban wastewaters tertiarily treated with Scenedesmus sp.

The productivity and composition of Daphnia magna were measured for high density populations grown in 5-litre flow-through tanks supplied with a tertiary effluent. This effluent was urban secondary wastewaters biologically treated with intensive cultures of a microalga Scenedesmus sp.Three daily feeding rates (575, 1150, 1750 mg dry weight algae day^?1 tank^?1), obtained by adjusting the flow of a tertiary effluent containing 115 mg dry weight of algae litre^?1, allowed average productions of 0·9, 1·6 and 2·6 g of Daphnia (wet basis) litre^?1 week^?1 which were proportional to the rations. When the flow of tertiary effluent was increased to 40 litres day^?1 tank^?1 (ad libitum), the average yield rose to 3·6 g of daphnids (wet basis) litre^?1 week^?1. The maximum population reached 48 000 individuals litre^?1. The daphnid/algae evergy conversion ratio was 0·4. Algae were removed by Daphnia at a maximum efficiency of 95%. The composition of Daphnia biomasses was 59·5% protein, 9·5% fat and 5·6% carbohydrate on a dry weight basis. No deficiencies in methionine and linolenic acid were noted.Results indicated the remarkable potential of urban wastewaters for the production of protein and the high productivity of Daphnia magna.     

Optimizing stocking density and microalgae ration improves the growth potential of tropical black‐lip oyster,Saccostrea echinata,larvae

The combined effects of stocking density and microalgae ration on survival and size of Saccostrea echinata larvae were studied in two‐factor experiments for the major developmental stages: D‐veliger (1‐day posthatch [dph], Experiment 1), umbonate (12 dph, Experiment 2), and eyed (19 dph, Experiment 3) larvae. Larvae were stocked into replicate sets of four 10‐L aquaria with ambient 1‐μm filtered sea water (28 ± 1.5°C and 36 ppt) and cultured for four days at densities of 0.5, 2, 5, 7, or 10 larvae/mL and provided with microalgae rations at each of five densities (cells larvae^?1 day^?1); 0, 1, 3, 5, or 8 × 10³ (D‐veliger larvae, Experiment 1); 0, 5, 12, 18, or 25 × 10³ (umbonate larvae, Experiment 2); and 0, 15, 30, 40, or 60 × 10³ (eyed larvae, Experiment 3). Microalgae rations for each larval life stage were selected on the basis of increasing food requirement with larval size and comprised a 2:1:1 mixture of Chaetoceros calcitrans, Tisochrysis lutea, and Pavlova spp., calculated on an equal dry‐weight basis. Contour plots were generated from larval survival and larval size (dorso‐ventral measurement [DVM]) data to determine optimal culture conditions. Larvae showed high survival (54–100%) over a wide range of both treatment parameters across all life stages, confirming broad tolerance limits for this species. The interaction effects of larval stocking density and microalgae ration on larval size were significant (p < 0.001) across all life stages. Results indicate that maximum larval size (DVM) is achieved when S. echinata are cultured at: 6–8 larvae/mL and fed 5–6 × 10³ cells larvae^?1 day^?1 for D‐veligers (mean DVM >80 μm), at 2–8 larvae/mL and fed 11–25 × 10³ cells larvae^?1 day^?1 for umbonate larvae (mean DVM > 190 μm), and at 1–4 larvae/mL and fed 15–40 × 10³ cells larvae^?1 day^?1 for eyed larvae (mean DVM >230 μm). Results will help refine current hatchery methods for S. echinata supporting further development toward commercial aquaculture production of this species.     

Efficiency of nitrification in trickling filters using different substrates

The efficiency of ammonium and nitrite oxidation was studied in two trickling filters filled with different plastic media (A, Hydropak^®-Folia, Uhde Dortmund, 200 m² active surface area per m³ volume; B, Bio-Net material, Norddeutsche Seekabelwerke, 260 m² m^?3). Both filters were operated simultaneously under comparable conditions (hydraulic load: of A = 40·2 m³ m^?3 day^?1; of B = 43·4 m³ m^?3 day^?1). Ammonium removal efficiency depended on pH value and on initial total ammonium concentration (range investigated: pH = 5·6–7·0; total ammonium concentration = 0·15?1·8 mg litre^?1; nitrite concentration = 0·08?1·85 mg litre^?1). Ammonium removal efficiency was reduced to almost zero at pH values below 5·6. Medium A was less efficient than medium B at higher pH levels (removal efficiency was above 50% at all times at pH values higher than 6·2, compared to 6·8 in medium A). With increasing initial ammonium concentration the removal efficiency decreased drastically in both filters (always below 60% at concentrations higher than 1·0 mg litre^?1). In general, nitrite oxidation efficiency followed a similar trend in both filters indicating a better performance of substrate B. Reasons for these differences are discussed.     

Correlation of in situ respiration rates and microbial biomass in prawn (Macrobrachium rosenbergii) ponds

Microbial biomass estimates (based on ATP concentrations) were highly correlated with water and sediment respiration rates in freshwater prawn ponds. Water column biomass-specific respiration rates (x ± 1 SD, 572.4 ± 410.6 μl O₂ μg ATP^?1 day^?1) were higher than sediment rates (11.5 ± 8.1 μl O₂ μg ATP^?1 day^?1). Phytoplankton cells dominated the seston, with nutrient-saturated, light-limited growth in the range 75–80%μ_max. Doubling times of phytoplankton ranged from 0.4–19 days. Measurement of benthic ATP biomass is recommended as a diagnostic water quality parameter for commercial freshwater prawn culture.     

Intensive carp Cyprinus carpio (L.) rearing in a farm pond in southern Germany and its effects on water quality

Experiments over three years, in a pond of approximately 1500 m², to intensify production at high stocking densities with controlled feeding resulted in a substantial increase in yield (weight gain per hectare and year: 2·6 tonne for C_3–4, 9·1 tonne for C_2–3, 15·4 tonne for C_1–2). At the same time water requirement could be reduced to 4 m³ kg^?1 fish produced. However, the stocking densities achieved resulted in a continuously increasing eutrophication effect which expressed itself in mass development of phytoplankton. This led to considerable diurnal fluctuations in oxygen concentration (0·5–20·0 mg O₂ litre^?1) and total ammonia (0–11·0 mg NH₃NH₄⁺ litre^?1; maximum of 1·5 mg NH₃ litre^?1). The high stocking density contributed indirectly to the diurnal fluctuations (fertilization through faeces and lost feeds). However, its contribution to the overall oxygen depletion amounted to less than 25% at night. The amplitude of the fluctuation was mainly determined by the photosynthetic and respiratory activity of the phytoplankton and by microbiological degradation processes. With increasing water temperature during summer, increasing feeding rate, continuous fish biomass increment, and decreasing light period per day and danger of total fish stock mortality was greatest in August. Only at maximum photosynthetic activity during daylight was the total ammonia production in the pond adequately counteracted and sufficient oxygen produced. Even heavy aeration could not always successfully provide for oxygen during night. In order to avoid a breakdown of the system, algae and nutrients had to be diluted from time to time by excessive water replacement. Despite the temporary overloading of the pond system, losses in numbers had been kept below 6·5% (normally: 10–20%).Pellets were offered via self-feeding devices. Food uptake was continuously recorded. No diurnal feeding rhythmic could be observed, but feeding activity was entirely dependent on oxygen levels in pond water. Feed conversion efficiencies reached values between 1·96 and 2·48.     

Influence of nitrogen availability on the biochemical composition of three unicellular marine algae of commercial importance

Chaetoceros calcitrans (Paulsen) Takano, Tetraselmis suecica (Kylin) Butch. and Isochrysis galbana Parke were grown in artificial seawater containing either normal (9·8 mg atoms litre^?1) or reduced (0·613 mg atoms litre^?1) nitrogen. When grown in the nitrogen-deficient medium protein decreased and carbohydrate increased in all three species; lipid, however, increased in Chaetoceros and Isochrysis but decreased in Tetraselmis.The biochemical composition of Tetraselmis and Isochrysis sampled during the post-exponential phase of growth from normal medium was similar to that of cells growing exponentially in nitrogen-deficient medium. Salinities of 10–35‰ did not affect protein levels in Tetraselmis or Isochrysis but carbohydrate increased and lipid decreased in Isochrysis over the salinity range. Temperatures of 18–25 °C had little effect on the cell composition of either species.The energy potentially available from a unit volume of Chaetoceros and Isochrysis cells from normal medium was similar to that from cells grown in nitrogen-deficient conditions in both species. Tetraselmis had 34% more energy available when grown in normal compared to nitrogen-deficient medium.     

Grow-out culture of tropical abalone, Haliotis asinina (Linnaeus) in suspended mesh cages with different shelter surface areas

Thisstudy investigated the effects of shelter surface area (SSA) on the feeding,growth and survival of the donkey-ear abalone, Haliotisasinina reared in mesh cages (0.38×0.38×0.28m) suspended in flow-through tanks (water volume = 6m³). Cages had sections of polyvinylchloride (PVC) thatprovided shelters with surface area of 0.22 m², 0.44m² and 0.66 m².Hatchery-produced abalone with initial shell length of 32 ± 1mm and wet weight of 7.5 g were stocked at 50individuals cage^?1 that corresponded to stocking densities ofca. 227, 113 and 75 abalone m^?2 of SSA. The ratios of sheltersurface area to cage volume (SSA:CV) were 5.5, 11 and 16.5. Abalones wereprovided an excess red seaweed Gracilariopsis bailinae(= Gracilaria heteroclada) at weekly intervals overa 270-day culture period. Feeding rates (18–20% of wet weight), foodconversion ratio (26–27) and percent survival (88–92%) did notdiffer significantly among treatments (p > 0.05). Body size at harvest rangedfrom 56 to 59 mm SL and 52 to 57 g wet body weightwith significant differences between abalone reared at SSA 0.22m² and 0.66 m² (p < 0.05).Abalone reared in cages with 0.66 m² SSA grewsignificantly faster at average daily growth rates of 132 μm and188 mg day^?1. Stocking densities of 75–113m^?2 SSA in mesh cages suspended in flow-throughtanks resulted in better growth of abalone fed red seaweed.     

Ammonia removal in selected aquaculture water reuse biofilters

Four fixed-film biological filters (rotating biological contactor, biodrum, trickling filter, and a submerged anaerobic filter) were tested for the removal of ammonia using a simulated warmwater fish and invertebrate culture water supply. Filter design may be determined based on the results of ammonia removal efficiency over a wide range of hydraulic loads. The rotating biological contactor (RBC) provided the best ammonia removal (over 90%) up to about 0·06 m³ m^?2 day^?1 (1·2 gpd ft^?2). The biodrum removed over 80% of the ammonia to a hydraulic load of 0·05 m³ m^?2 day^?1 (0·9 gpd ft^?2). The trickling filter removed 50% of the ammonia at a hydraulic loading of 0·012 m³ m^?2 day^?1 (0·3 gpd ft^?2).     

Effect of different broodstock densities on the reproductive performance of Nile tilapia, Oreochromis niloticus (L.), in a recycling system

The present study was conducted to evaluate the effect of different stocking densities on the seed production of Nile tilapia, Oreochromis niloticus (L.), under intensive recycling hatchery system conditions. Males and females with mean body weights of 163.2 and 105.0 g, respectively, were stocked at three broodstock densities (4, 8 and 12 fish m^–2) at a male:female ratio of 1:3 in 1 × 1 × 0.43 m (W × L × H) fibreglass tanks. The tanks were illuminated at 2500 lux for 18 h day^–1 and the water temperature was maintained at 29 ± 1 °C. Effluent from spawning tanks was recycled through a biological filter with 10–15% replacement of new water per day. The experiment lasted for 126 days. The results showed that breeders stocked at 4 fish m^–2 had significantly higher (P < 0.05) mean values for total seed production, seed kg^–1 female day^–1, seed female^–1 day^–1, seed m^–2 day^–1 and spawning synchrony than at 8 and 12 fish m^–2 broodstock densities. The mean percentage of seeds in the yolk-sac and swim-up fry stages was highest at 4 fish m^–2 broodstock density. However, the recovery rate was not affected by broodstock density. It is recommended that further research should be conducted to determine whether weight m^–2 , number m^–2 or age of broodstock should be the basis for stocking broodstock.     

Ammonia production and oxidation during the culture of marine prawns and lobsters in laboratory recirculation systems

Data obtained during the culture of tropical prawns Penaeus sp. and European lobsters Homarus gammarus (L.) in 20 laboratory recirculation systems over a number of years were used to obtain gross estimates of (a) the rates and diurnal patterns of ammonia excretion, (b) food utilization and wastage, and (c) nitrification rates in biological filters. Ammonia excretion in Penaeus monodon decreased with increase in animal size from 0·93 to 0·30 mg N g^?1 day^?1 at 1·6 and 27 g live weight, respectively. Large lobsters (300 g) excreted 0·3 mg N g^?1 day^?1. Peak excretion times were approximately 3, 9 and 15 h after a single morning feed for prawns and after 6 and 12 h for lobsters. Uneaten food solids amounted to 11% (lobsters) and 32% (prawns) of the daily ration and, for 4 g animals, only 69% (lobsters) and 45% (prawns) of the food nitrogen in the daily ration was converted into crustacean flesh. Nitrification rates ranged from 0·03 to 0·43 g N oxidized per m² of filter media surface per day. Some evidence for periodicity in nitrifying activity was also found and is discussed in relation to the published literature.     

Demographic and competition studies on <Emphasis Type="Italic">Brachionus ibericus</Emphasis> and <Emphasis Type="Italic">Proales similis</Emphasis> in relation to salinity and algal (<Emphasis Type="Italic">Nannochloropsis oculata</Emphasis>) density

We isolated the rotifers Brachionus ibericus and Proales similis from the sediment of shrimp tanks and studied their individual demographic characters and competition between them at two food levels (0.25?×?10⁶, 1.00?×?10⁶ cells ml^?1 of Nannochloropsis oculata at 25 °C) and salinities ranging from 10 to 30‰. Our hypothesis was that growth rates would be higher with increasing food levels and salinities. Observations were taken twice a day for life table studies and daily once for population growth experiments. Using survivorship and fecundity data, we derived various life history variables. Although the average life span (7.6?±?0.4 days) and gross reproductive rate (33.8?±?2.9 neonate female^?1 day^?1) of B. ibericus were higher than those of P. similis (average life span 5.4?±?0.6 days and gross reproductive rate 13.0?±?0.6 neonate female^?1 day^?1), the population growth experiments showed that P. similis had higher r values (0.32?±?0.005 day^?1) than B. ibericus (0.23?±?0.002 day^?1) at 1.0?×?10⁶ cells ml^?1 of N. oculata. The rotifer P. similis was more adversely affected due to the presence of B. ibericus than vice versa. The data are important for developing techniques for a large-scale culture of these rotifers as food in aquaculture.     

The impact of light intensity and algal-induced turbidity on first-feeding Seriola lalandi larvae

Feeding performance (intensity and incidence) of first‐feeding yellowtail kingfish larvae was evaluated under a range of light intensities and algal‐induced turbidities. Larvae were fed with varying degrees of success under all light intensities tested (0–17 μmol s^?1 m^?2), in both clearwater and greenwater (8 × 10⁴ cells mL^?1). There was a consistent trend for feeding performance to increase with larval age and light intensity in both clearwater and greenwater conditions, demonstrating that visual proficiency increases with larval age. Feeding intensity remained low over the first 3 days of first feeding across all light intensities tested. Days 6 and 7 post‐hatch larvae showed considerably higher feeding intensities particularly at 8 and 17 μmol s^?1 m^?2. This improvement indicates an ontogenetic shift in sensory or locomotor competence. First‐feeding larvae performed equally well in both clearwater and greenwater (8 × 10⁴ cells mL^?1) conditions, although at the lowest light intensity tested (0.1 μmol s^?1 m^?2) feeding performance was noticeably reduced. Feeding performance was severely diminished across all larval ages at an algal cell density of 32 × 10⁴ cells mL^?1, demonstrating that for this species algal‐induced turbidities >16 × 10⁴ cells mL^?1 adversely affect the ability to capture free‐swimming prey during the first‐feeding window.     

Growout production of camouflage grouper, Epinephelus polyphekadion (Bleeker), in a tank culture system

Growout production of the camouflage grouper, Epinephelus polyphekadion (Bleeker), in a 10-m³-capacity fibreglass tank culture system was evaluated, using hatchery-produced fingerlings (56-59 g initial weight) at stocking densities of five, 15 and 45 fish m^?3. During the first 9 months of a 12-month growout period, the fish were fed twice a day with a moist pellet feed containing 40.9% protein. From month 10 onwards until harvest, the fish were fed moist pellets in the morning and trash fish in the evening at a 1:1 ratio. The final weight of fish at harvest was up to 900 g, with mean weights of 544.6 ± 170.72 g at five fish m^?3, 540.2 ± 150.82 g at 15 fish m-^?3 and 513.3 ± 134.52 g at 45 fish m^?3. The results showed no significant differences (P > 0.05) in growth rate and fish size between the different stocking densities tested. The average daily growth rate ranged from 0.62 to 3.38 g fish^?1 day^?1, with mean weights of 1.49 ± 0.74 g fish^?1 day^?1 at five fish m^?3 through 0.53 to 2.38 g fish^?1 day^?1, 1.32 ± 0.57 g fish^?1 day^?1 at 15 fish m^?3 to 0.48-3.32 g fish^?1 day^?1 and 1.31 g fish^?1 day^?1 at 45 fish m^?3 stocking density. Although up to 100% survival was observed at the lowest stocking density, the survival rate significantly decreased (P < 0.05) with increasing stocking density. The food conversion ratio (FCR) significantly decreased (P <0.05) with increasing stocking densities, showing efficient feed utilization with increasing stocking densities of E. polyphekadion. The FCR averaged 2.1 at a stocking density of 45 fish m^?3. The yield in terms of kg fish produced m^?3 of water used in the culture system significantly increased (P < 0.001) from five to 45 fish m^?3. The yield averaged 17.3 ±0.53 kg m^?3 at a stocking density of 45 fish m^?3. The present results show that the present tank culture system could sustain more biomass in terms of increasing fish stocking densities. The growth performance of E. polyphekadion observed during this investigation has been reviewed with other grouper species.     

Effects of salinity,stocking density,and algal density on growth and survival of Iwagaki oyster <Emphasis Type="Italic">Crassostrea nippona</Emphasis> larvae

To determine the optimal salinity, stocking density, and algal density for hatchery culture of the Iwagaki oyster Crassostrea nippona larvae, three experiments with salinities of 14, 18, 22, 26, 30, and 34 practical salinity unit (PSU); stocking densities of 0.5, 1, 2, 4, 8, and 12 larvae ml^?1; and algal densities of 10, 20, 40, and 100?×?10³ cells ml^?1 were designed, which included the developmental stages from newly hatched D-larvae to pediveligers. Results showed that larval growth of C. nippona was the fastest at a salinity of 26 PSU, and when salinity was adjusted to a level that was lower or higher than this salinity, survival and growth rate of larvae declined (P <?0.05), resulting both in a decreased mean shell length and a high mortality. Larval growth decreased significantly with increasing stocking density. Larvae reared at 4 larvae ml^?1 had the smallest shell length (198.9 μm) and lowest survival rate (7.9%), whereas larvae reared at 0.5 larvae ml^?1 had the largest shell length (245 μm) and highest survival rate (66.3%) on day 13. And the shell length of larvae reared at 0.5 and 1 larvae ml^?1 was significantly (P?<?0.05) larger than the values in other treatments, except those reared at 2 larvae ml^?1 (P?>?0.05). When feeding the single-algal diet of Isochrysis galbana (clone T-ISO), the shell length of larvae increased markedly as the algal density was increased. Larvae reared at the highest algal density (100?×?10³ cells ml^?1) had the largest mean shell length; however, under the conditions of our experiment, there was no significant difference (P?>?0.05) in growth and survival rates between the treatments at algal densities of 40?×?10³ and 100?×?10³ cells ml^?1. For a large-scale culture, based on the results of this study, a salinity of 26 PSU, stocking density of 0.5–1 larvae ml^?1, and algal density of 40?×?10³ cells ml^?1 are recommended for an early development of C. nippona.     

The influence of \upbeta-hydroxy- \upbeta-methylbutyrate (HMB) on cell-mediated immunity in tench Tinca tinca (L.): in vitro and in vivo study

$\upbeta$ -Hydroxy- $\upbeta$ -methyl butyrate (HMB) has been shown to counteract many of the negative effects of intensive fish production methods and results in increased growth and protection against diseases. In the present study, the in vitro and in vivo effect of HMB on the immunocompetence cell activity in tench Tinca tinca (L.) was examined. In the in vitro study pronephric phagocytes and lymphocytes were isolated from the fish and grown in culture medium (RPMI-1640) containing 0, 0.1, 1, 5, 10, 25, 50 or $100\,\upmu$ g HMB cm^?3 of medium. The effects of HMB on the respiratory burst activity (RBA), the potential killing activity (PKA) and lymphocyte proliferation stimulated by concanavalin A (ConA) or lipopolysaccharide (LPS) were examined. The in vitro study showed that HMB increased the RBA and PKA of the phagocytes, compared to the medium over that of cells grown without HMB. Lymphocyte proliferation stimulated by ConA and LPS was also increased approximately when HMB was added to the culture medium at concentrations between 10 and $100\,\upmu$ g HMB cm^?3. In the in vivo study fish were fed daily with pellets containing HMB at doses 0, 10, 25 and 50 mg kg^?1 body weight day^?1. The study showed that HMB statistically increased the RBA and PKA and highest activity at 50 mg kg^?1 body weight day^?1 were observed. Also lymphocyte proliferation stimulated by ConA and LPS were maximally stimulated at dose 50 mg kg^?1 body weight day^?1. In conclusion, the current study shows that HMB could potentially improve immunocompetence cell activity in tench through increased cell proliferation and functionality.     

High-density growth and crude protein productivity of a thermotolerant Chlorella vulgaris: production kinetics and thermodynamics

Current study investigated the fermentative production of cell mass and crude protein using an axenic culture of the thermotolerant strain of Chlorella vulgaris grown mixotrophically in an illuminated 10-l glass bioreactor. The process was then upscaled to 1,000-l bioreactor. The organism supported maximum specific growth rate, crude protein volumetric productivity, and specific productivity of 1.2?day^?1, 2.26?g?l^?1?day^?1, and 0.76?g?g^?1?day^?1, respectively, with urea as nitrogen source. Gibbs free energy, enthalpy, and entropy values for its formation were 74.3, 56. 2?kJ?mol^?1, and ?59.1?J?mol^?1?K^?1, respectively, in both reactors and corresponded to those of thermotolerant organisms. Algal biomass grown in 10-l bioreactor contained 0.52?±?0.03, 12.6?±?2.0, 60.0?±?4.5, 0.4?±?0.02, 4.5?±?0.2, 12?±?0.5, and 3.81?±?0.5% carotenoids, carbohydrates, crude protein, DNA, RNA, lipids, and total chlorophyll, respectively. Dry biomass supported good growth of fish larvae comparable with that on commercial diet.     

Oxygen consumption and ingestion rate of Penaeus setiferus larvae fed Chaetoceros ceratosporum, Tetraselmis chuii and Artemia nauplii

The effects of the density and type of food on oxygen consumption and ingestion rate of larvae of the white shrimp Penaeus setiferus fed diatoms Chaetoceros ceratosporum, flagellates Tetraselmis chuii and Artemia franciscana nauplii were analysed. Diatoms, flagellates and Artemia nauplii were fed at five densities from 10 to 5 × 10³ cells mL^?1, 0 to 4 × 10³ cells mL^?1, and 0.1, 0.5, 1.0, 1.5 and 2 nauplii mL^?1, respectively. In three experiments, two of three types of food were maintained constant at concentrations of 30-40 × 10³ cells mL^?1 (diatoms), 2 × 10³ cells mL^?1 (flagellates) and 1 Artemia nauplii mL^?1. The oxygen consumption in three experiments increased with larval stage, reaching maximum values in Mill except at lower feed concentrations. A maximum ingestion peak in MI was recorded in larvae fed diatoms, whereas that peak was observed in Mil in larvae fed flagellates. The maximum ingestion rate of Artemia nauplii was observed in Mill. Feed concentrations that produced an optimum metabolic rate as a consequence of equilibrium between ingested food and larval stages were obtained with 20 and 30 × 10³ cells mL^?1 of C. ceratosporum, 2 and 3 × 10³ cells mL^?1 of T. chuii, and 1.0 Artemia nauplii mL^?1. These concentrations would be the most suitable for producing P. setiferus postlarvae.     

The effects of feeding frequency on growth of juvenile Atlantic halibut, Hippoglossus hippoglossus L.

Four experiments were conducted to investigate the effects of feeding frequency on growth of juvenile Atlantic halibut, Hippoglossus hippoglossus L. Fish (22–75 g) fed three (3 ×) or five times per day (5 × day^?1) under constant light and temperature (13±1°C) consumed significantly more feed than fish fed 1 × day^?1 but by the end of the experiment only fish fed 5 × day^?1 were heavier and had greater specific growth rates (SGR). Under simulated winter conditions (9L:15D, 5±1°C), halibut (～300 g) fed every other day consumed more feed, had a greater SGR and final weight compared with fish fed every third day. Feed conversion ratios were not different among treatment groups in any of the experiments. These results suggest that growth rates may be improved by feeding juvenile halibut more than 1 × day^?1.     

A technical solution to the mass-culturing of larval turbot

A 1000 litre recirculation system of eight cylindrical rearing tanks has been tested in three 40-day periods to determine its capacity for rearing larval turbot (Scophthalmus maximus L.).The larvae were fed on rotifers and Artemia nauplii, as well as mixed marine algae. Continuous artificial light of 1500–2000 lux was applied at the surface. The applied algae served a dual function; keeping rotifers and Artemia at a high nutritional level as well as effectively removing the released ammonia. The combination of upwelling water and light at the surface maximized the contact surface between larvae, food items and algae.With this system, using a stocking density of 16 larvae litre^?1 in the rearing tanks, a survival total of 40% at Day 40 was achieved, giving a production of 6·4 larvae litre^?1 or 3000 larvae metre^?2 of the surface of the rearing tanks.     

Optimum culture conditions of <Emphasis Type="Italic">Rhodomonas</Emphasis> sp. Hf-1 strain as a live food for aquatic animals

Suitable culture conditions for Rhodomonas sp. Hf-1 strain were examined for high productivity. Hf-1 strain was grown in an incubator for 7 days. The factorial experimental design investigated the following 19 variables: temperature (12, 16, 20, 24 and 28 °C), salinity (7, 14, 21, 28 and 35 psu), light intensity (20, 35, 50, 65 and 80 μmol m^?2 s^?1), light color (white, red, green and blue lights), and 3 factorial designs of photoperiod (24L:0D, 16L:8D and 12L:12D light:dark cycle). The cell density and specific growth rates (SGR) were analyzed. The best cell growth was observed under the following culture conditions: temperature of 24 °C, salinity of 21 psu, light intensity of 80 μmol m^?2 s^?1, and white light. In the photoperiod test, the highest cell density of 4.7?×?10⁶ cells ml^?1 was obtained at 24L:0D light:dark cycle, and the SGR was 0.57 μ day^?1 at this time. We found that the Hf-1 strain was able to be cultured in extremely wide culture conditions. These results are expected to serve as a baseline study for culturing the Hf-1 strain in the laboratory and for its use in aquaculture.