Food ingestion,consumption and selectivity of pompano,Trachinotus ovatus (Linnaeus 1758) under different rotifer densities

The growth, survival, food selection and consumption of pompano larvae under different rotifer densities as well as their colour preference during the rotifer feeding stage were examined in this study. Growth and survival of fish larvae were not significantly affected when rotifer density was between 10 and 20 mL^?1. Fish larvae grew slower at 1 and 40 rotifers mL^?1 than at 10 and 20 rotifers mL^?1, and higher fish survival was achieved when fish larvae were exposed to 10 and 20 rotifers mL^?1. The rotifer density of 1 mL^?1 not only reduced food ingestion during the early stage, but also delayed diet switch from rotifer to copepod nauplii. On 5 days post hatching (DPH), larval pompano ingested more rotifers in dark‐coloured tanks and ingested more rotifers when prey colour was green. Based on the results obtained in the present study, the culture of larval pompano larvae is recommended using dark wall tanks with a feeding density of 10–20 rotifers mL^?1 during the initial feeding stage. This study proposes a management protocol to use appropriate type and quantity of live food to feed pompano larvae in a hatchery rearing condition, which could be applicable to the culture of fish larvae in other marine fish species.     

The effect of different rotifer feeding regimes on the growth and survival of yellowtail kingfish Seriola lalandi (Valenciennes, 1833) larvae

First feeding success is critical to larval marine finfish and optimization of live feed densities is important for larval performance and the economics of commercial hatchery production. This study investigated various rotifer feeding regimes on the prey consumption, growth and survival of yellowtail kingfish Seriola lalandi larvae over the first 12 days post hatch (dph). The common practice of maintaining high densities of rotifers (10–30 ind. mL^?1) in the rearing tank was compared to a low density feeding technique, where 5–8 ind. mL^?1 of rotifers were offered. A ‘hybrid’ feeding regime offered rotifers at the high density treatment until 5 dph and the lower feeding densities thereafter. There was no significant difference in larval survival (hybrid: 28.9 ± 7%, low density: 17.3 ± 5% and high density: 17.2 ± 9%) or growth (hybrid: 6.12 ± 0.18 mm, low density: 6.03 ± 0.10 mm and high density: 6.11 ± 0.23 mm) between treatments. Rotifer ingestion was independent of rotifer density throughout the trial and increased with larval age, with larvae at 4 dph ingesting 22 ± 1.5 rotifers larvae^?1 h^?1 and by 11 dph ingesting 59 ± 1.6 rotifers larvae^?1 h^?1. These data demonstrate that from first feeding, yellowtail kingfish larvae are efficient at capturing prey at the densities presented here and consequently significant savings in rotifer production costs as well as other potential benefits such as facilitation of early weaning and improved rotifer nutritional value may be obtained by utilizing lower density rotifer feeding regimes.     

Food consumption and selectivity by larval yellowtail kingfish Seriola lalandi cultured at different live feed densities

Live food supply is a key factor contributing to the success of larval fish rearing. However, live food densities vary greatly between fish species and management protocols across fish hatcheries. The growth, survival, food selection and consumption of yellowtail kingfish larvae were examined at different regimes of live food supply in an attempt to identify a suitable live food feeding protocol for larval rearing in marine fish. This study was divided into two feeding phases: rotifer phase from 3 to 14 DPH (phase I) and Artemia nauplii phase from 15 to 22 DPH (phase II). In phase I, four rotifer densities (1, 10, 20 and 40 mL⁻¹) were used. In phase II, Artemia started at 0.8 nauplii mL⁻¹ on 15 DPH, and then the density of Artemia was daily incremented by 50%, 70%, 90% and 110%, respectively, in four treatments from 15 to 22 DPH. In phase I, rotifer density significantly affected larval growth, but not survival. By 7 DPH, the number of rotifers consumed by fish larvae reached 170–260 individuals, but did not significantly differ between rotifer densities. During cofeeding, fish larvae selected against Artemia nauplii by 10 DPH, but by 14 DPH Artemia nauplii became the preferred prey item by fish larvae exposed to the 10, 20 and 40 rotifers mL⁻¹. In phase II, both fish growth and survival were affected by Artemia densities. Fish daily consumption on Artemia by 20 DPH reached 500–600 individuals but did not significantly differ between prey densities. The result suggests that rotifer densities be offered at 20–40 mL⁻¹ before 6 DPH and 10–20 mL⁻¹ afterwards to support larval fish growth and survival. Likewise, Artemia is recommended at a daily increment of 90–110% of 0.8 mL⁻¹ from 15 to 22 DPH. This study proposes a management protocol to use appropriate type and quantity of live food to feed yellowtail kingfish larvae, which could be applicable to larval culture of other similar marine fish 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.     

Enrichment of the nematode Panagrolaimus sp., a potential live food for marine aquaculture,with essential n-3 fatty acids

The nematode Panagrolaimus sp. (strain NFS-24-5) may have potential as a live food organism for larvae of several marine species. It can be mass-produced in liquid culture and is desiccation tolerant enabling long-term storage and transportation. Nematodes lack the essential fatty acid docosahexaenoic acid (DHA), so this investigation examined an enrichment procedure by incubating nematodes in S.presso^® (INVE Aquaculture, Belgium), a commercial enrichment product. Mass-produced nematodes from liquid cultures on yeast cells were cleaned and then exposed to concentrations of 0.1–3 % S.presso^® for 24 h at 200,000 nematodes ml^?1. Nematode viability was >90 % after the treatment. Following enrichment percentage, total lipid ranged from 23.6 to 33.3 % of nematode dry matter, and nematodes incubated in 3 % S.presso^® had a significantly higher lipid percentage than untreated controls. Enrichment was successful in increasing the percentage of DHA, and a maximum value of 5.8 % of total fatty acids was achieved. The results of enrichment of Panagrolaimus sp. (strain NFS-24-5) following treatment with 3 % S.presso^® should promote the carrying out of feeding trials to test the efficacy of the nematodes as a live food for larval marine fish and crustaceans.     

Evaluation of nutritional and environmental variables during early larval culture of pigfish Orthopristis chrysoptera (Linnaeus)

Pigfish (Orthopristis chrysoptera Linnaeus) are a commonly used baitfish in the southeastern United States. Aquaculture methods for broodfish spawning and juvenile grow‐out have been developed but there is still a paucity of information regarding larval culture methods. Five, short duration (10 days) experiments were conducted to determine effective strategies to yield high larval survival and growth during early development. Experiment one examined the rotifer enrichments Ori‐Green, DHA Protein Selco, and AlgaMac 3050 as well as a non‐enriched control along with corresponding fatty acid levels in the enriched rotifers and pigfish larvae. Experiment two evaluated three, once daily feeding frequencies of either 5, 10 or 20 rotifers mL^?1. Experiment three compared feeding 20 rotifers mL^?1 once daily to feeding 5 rotifers mL^?1 twice daily. Experiment four examined four different larval stocking densities: 50, 75, 100, or 125 larvae L^?1. Experiment five examined green water strategies using either live Tahitian strain Isochrysis galbana (Parke) or Nannochloropsis oculata (Hibberd) paste at either 250 000 or 500 000 cells mL^?1 as well as a clear water control. Results indicated rotifer enrichment with DHA Protein Selco and green water application using live T‐ISO at 500 000 cells mL^?1 had the highest survival of pigfish during early stages of larval culture. A once daily rotifer feeding regime of 20 rotifers mL^?1 and stocking density of 50 larvae L^?1 also improved survival. These results provide producers with methods to improve efficiency for pigfish larval culture and provide researchers with new foundational data, such as potential fatty acid requirements.     

Swimbladder inflation associated with body density change and larval survival in southern bluefin tuna Thunnus maccoyii

High mortality of southern bluefin tuna (SBT) Thunnus maccoyii larvae in captivity is a major problem hindering culture of this species. The relationships between body density of SBT larvae, swimbladder inflation and survival were investigated in this study. Swimbladder inflation and changes in volume have a direct effect on body density in larval SBT. Swimbladder inflation was first observed at 3 days post hatch, and larvae with successful swimbladder inflation were able to maintain their body density within a narrow range (?ρ = 0.0006 g cm^?3). Although swimbladder volume increased with larval growth, it could not compensate for the increase in body density and did not prevent nocturnal sinking. The increase in body density was greater for larvae that did not inflate their swimbladder. Low percentages of swimbladder inflation (27.5 ± 3.5 %) coupled with negative body buoyancy of SBT might contribute to mortality as larvae sank in the dark phase and made contact with the tank bottom. Management strategies that maintain larvae within the water column and enhance swimbladder inflation are required to improve survival of SBT larvae reared in hatcheries.     

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.     

Changes in the Population Structure of the Lineage ‘Nevada’ Belonging to the Brachionus plicatilis Species Complex, Batch-Cultured Under Different Feeding Regimes

Two experiments were conducted examining the population structure of Brachionus ‘Nevada’ under feeding conditions commonly applied in hatcheries, using 4-day rotifer batch cultures. In the first experiment two diets were supplied: yeast with Tetraselmis suecica (treatment A) or Culture Selco^® with T. suecica (treatment B). The second experiment (treatments C, D, E) differed in the phytoplankton quantity used (20?times higher): treatment C was analogous to A and treatments D and E to B. Initial rotifer density differed among treatments and was about 200 individuals ml^?1 in A, C and E, and 60 individuals ml^?1 in B and D. Multivariate analysis discriminated A and C from B, D and E. In treatments A and C, a 24-h cycle in ovigerous females, immature individuals and E/F ratio was observed, showing a high reproductive rate. Treatments B, D and E displayed a 48-h cycle in the aforementioned parameters, indicating a lower reproductive rate. The latter treatments had a significantly higher number of females with multiple eggs for most of the samplings, compared to A and C, except for treatment E until 40 h of sampling. Specific growth rate was significantly higher in treatments B and D (Culture Selco^® diet) compared to A and C (yeast diet), while treatment E had intermediate rates. Initial rotifer density influenced the abundance of females with multiple eggs, but resulted in slight variations in growth rate and population structure. The type of dry food greatly affected the population structure of rotifers, leading to significant differences in the growth rate.     

Baseline culture parameters for the cyclopoid copepod Oithona colcarva: a potential new live feed for marine fish larviculture

Feeding copepods during early larval culture stages of marine fish has proven to be advantageous for growth and survival of marine finfish larvae. However, commercial availability of most copepods is limited; thus, there is an impetus to evaluate promising copepod species to meet the diverse dietary demands of various marine fish. The marine cyclopoid copepod, Oithona colcarva, was isolated out of zooplankton samples taken from waters within Tampa Bay, Florida. Once isolated, trials were conducted to determine the appropriate culture parameters for producing nauplii to feed marine fish larvae. The effects of temperature (22°C, 26°C and 30°C), salinity (15, 20, 25, 30 and 35 g L^?1), stocking density (0.5, 1.0, 2.0, 4.0 and 8.0 individuals mL^?1) and diet (Nanno 3600 microalgae paste, Colurella adriatica, Rhodomonas lens, Tisochrysis lutea, Chaetoceros gracilis and/or Tetraselmis chuii) on nauplii production during a single life cycle of reproducing individuals were examined. Results of those trials indicated that a culture temperature of 30°C and a salinity of 30 g L^?1 were advantageous for maximum nauplii production. Furthermore, a diet containing a 1:1:1 mixture of T. lutea, C. gracilis and T. chuii and a stocking density of at least 8 individuals mL^?1 were identified as beneficial. The results of these trials, the potential for large‐scale culture and observations on the performance of marine fish larvae fed Oithona colcarva nauplii are discussed.     

Effects of stocking density, diet, and water exchange on growth and survival of pearl oyster Pinctada maxima larvae

Three experiments were carried out to separately investigate the effects of stocking density (1.0, 2.0, 4.0 and 8.0 larvae ml^?1), diet (Isochrysis zhanjiangensis, Chlorella spp., Nannochloropsis oculata, 50 % I. zhanjiangensis/50 % Chlorella spp. and 50 % I. zhanjiangensis/50 % N. oculata), and water exchange (25 % once every other day and 25, 50 and 100 % once daily) on growth and survival of pearl oyster Pinctada maxima larvae. Results showed that there existed significant effects of stocking density, diet, and water exchange on the growth of pearl oyster larvae (P < 0.05). Larval survival was significantly affected by stocking density and diet (P < 0.05), but not by water exchange (P > 0.05). Larval growth decreased significantly with increasing stocking density (P < 0.05). A density of 1.0–4.0 larvae ml^?1 was optimal for larval growth of pearl oyster. Chlorella spp. and N. oculata could replace 50 % of I. zhanjiangensis as a food source for the pearl oyster larvae without affecting growth and survival. A water exchange of 25 % once daily provided optimum larval growth and survival.     

Implications of larval diet concentration on post-larval yield in a production scale flow-through system for scallops (Pecten maximus Lamarck) in Norway

In order to optimize Pecten maximus larval performance and post-larval yield, larvae were fed five algal concentrations in the range 3–20 cells μL^?1 in 2,800-L flow-through tanks without prophylactic antibiotics. Competent larvae were transferred to a commercial hatchery for settlement and provided uniform conditions for 4 weeks to observe effects. Increased diet concentration increased the sum of fatty acids (FA) in the total larval population, reaching 7 and 25 ng FA larvae^?1 at 3 and 16 cells μL^?1, respectively. The FA level in competent larvae was not affected by diet concentration and ranged from 30 to 46 ng larvae^?1. Increased diet concentration increased larval growth rate, and the larvae were ready to settle 5 days earlier when fed 16 cells μL^?1 compared to 3 cells μL^?1. Larval ingestion rate increased during life span and with increased larval diet concentrations, but a considerable amount (40–60 %) of the added algal cells was lost from the larval rearing tanks due to the seawater flow. There was no effect on larval survival, final post-larval shell height, % of competent larvae transferred to settlement, or total yield of post-larvae. Final mean post-larval shell height was 509 μm and 25.5 % of competent larvae settled, resulting in a final post-larval yield between 6.9 and 17.6 % of the initial number of d3 larvae. Competent larvae with similar FA content produced similar numbers of post-larvae independent of diet concentration, even if higher diet concentrations resulted in higher rates of larval development and metamorphosis.     

Effect of different live food on survival and growth of first feeding barber goby,Elacatinus figaro (Sazima,Moura & Rosa 1997) larvae

One of the major challenges in marine fish culture is how to provide live food of adequate size and nutritional quality for first‐feeding larvae. Commonly used live food organisms, rotifers and brine shrimp, may not always be the best option. To determine the suitability of different zooplankton in the larviculture of Elacatinus figaro, three diets were tested: RE – rotifers Brachionus sp. (10 ind mL^?1)+ciliate Euplotes sp. (10 ind mL^?1), enriched with fatty acids; RC – enriched rotifers (10 ind mL^?1)+wild copepod nauplii (10 ind mL^?1); and R – enriched rotifers (20 ind mL^?1). Survival rates were estimated 10 days after hatch (DAH) for the three test groups, and growth rates were evaluated for RE and R at 10 and 20 DAH. Although survival rate was numerically higher for the RC diet (41.1±14.2%), no significant difference was detected between groups fed RE (20.5±18.1%), RC or R (32.1±16.5%). At 10 DAH, the growth rate was significantly higher in RC (5.7±0.6 mm) than in R (4.6±0.5 mm), a trend that was also observed at 20 DAH for RC (8.6±0.5 mm) and R (5.8±0.7 mm) (P<0.05). E. figaro larvae fed on ciliates did not show satisfactory results, whereas feeding copepod nauplii enhanced growth.     

Nutrition of Marine Fish Larvae

ABSTRACT

In the hatchery production of aquatic animals for aquaculture, livefoods such as diatoms; rotifer, Brachionus plicatilis and brine shrimp, Artemia salina, have been used throughout the world. However, such production requires large facilities, maintenance expenses, and labor to produce a desired amount of live foods constantly and reliably. Also, the nutritive value of planktonic organisms is occasionally variable, indicating that the dietary quality of these live foods varies with the content of n-3 highly unsaturated fatty acid (n-3 HUFA). Therefore it is necessary to develop microparticulate diets as a substitute for live foods to further increase theproductivity of seed for fish culture. The nutritional components of microparticulate diets for fish larvae should be determined on the basis of requirements of the larval fish for proteins and amino acids, lipids and fatty acids, carbohydrates, vitamins, and minerals. Moreover, the efficient development of microparticulate diets for the fish larvae has promoted the improvement of nutritional requirement studies. The present reviewconcerning the nutrition of marine fish larvae focuses on the proteins, amino acids, peptides, fatty acids, phospholipids, depigmentation of flatfish, stress tolerance of lipids, incorporation of HUFA in neural tissues, HUFA in egg and larvae, HUFA enrichment of live food, carbohydrates, vitamins, energy source during embryo and larval stages, enzyme supplement in microparticulate diets, and application of microparticulate diets inaquaculture.     

Semi‐continuous mass culture of rotifers (Brachionus plicatilis) using an automatic feeder

This study describes the rotifer mass culture protocol developed at the Institute of Aquaculture (HCMR) in Crete. Rotifers were cultured semi‐continuously at a density of 257.6 ± 2.6 ind. mL^?1, with a daily dilution rate of 25%. An automatic feeder was used to administer dry feed (Selco Sparkle^®) every 10 min. A number of factors were investigated so as to provide an in‐depth analysis of the advantages and disadvantages of the two systems, especially when compared with traditional protocols such as batch culture. The use of these two systems resulted in a culture of considerable duration (41 days) and daily yield (0.21 ± 0.01 ind. 10⁶ day^?1 L^?1), using exclusively dry feed. Both systems can be easily applied in hatcheries, requiring few modifications on existing protocols and contribute to a stable and predictable production. Further improvements include manipulation of the dilution rate, food ration, culture volume and duration, as well as choice of a phytoplankton‐based diet.     

Low-temperature preservation (at 4 °C) of marine rotifer Brachionus

Mass production of rotifers is essential as live food during the larval rearing season, but a major problem of rotifer culture is unpredictable culture collapse. If mass‐produced rotifers could be kept alive at low temperature for an extended period of time, they could be supplied as live food to cultured marine fish larvae without interruption. Four experiments were performed to test this possibility in six strains of Brachionus plicatilis O. F. Müller and eight strains of Brachionus rotundiformis Tschugunoff. The results showed that: (1) B. rotundiformis strains were less tolerant to 4 °C than B. plicatilis strains. Among the B. rotundiformis strains, the strains known as SS type were the most susceptible and showed the lowest survival. (2) Exchange of culture media during the incubation at 4 °C in B. plicatilis and B. rotundiformis resulted in higher survival than not changing the culture media, but there were no differences in the regression slope with or without changing the culture media. (3) Acclimation at 15 °C for 96 h for B. plicatilis and B. rotundiformis before transfer to 4 °C resulted in higher survival rates than acclimation at 10 °C. (4) The combination of frequent exchange of culture media and acclimation significantly improved the survival of B. plicatilis and B. rotundiformis compared with controls that were maintained at 4 °C without exchange of the culture media. Large‐scale trials using B. plicatilis (Kamiura strain) cultured in 30‐L tanks were conducted in a hatchery at a density of 2000–20 000 individuals mL^?1. Rotifers were transferred directly from 25 °C to 4 °C. About 50% of the rotifers at 20 000 individuals mL^?1 survived after 14 days at 4 °C. These preserved rotifers could be cultured at 20 °C, recovering within 4 days.     

Strategies and Tactics for Larval Culture of Commercially Important Carp

This paper reviews state-of-the-art techniques for culture of larval common carp, Cyprinus carpio, silver carp, Hypophthalmichthys molitrix, bighead carp, H. nobilis, and grass carp, Crenopharyngodon idella. Water temperature, food, and predation are important factors influencing larval survival and growth. Lower and upper lethal temperatures range from 3 to 44°C. Optimum growth temperatures range from 38 to 40°C. Lethal and optimum temperatures vary with acclimation temperature, fish age, and development stage of fish. Water temperatures are close to optimum for larval culture in tropical regions but are often too low in temperate climates. Intensive culture in temperature-controlled systems is important in temperate climates. The first food eaten by larvae in ponds consists mainly of protozoa, rotifers, and copepod nauplii. As fhe larvae grow, they quickly shift to larger food items, including cladocera and insect larvae. Management practices to enhance natural food development in earthen ponds include bottom drying, soil preparation, liming, fertilization, and agricultural crop cultivation. The development of food organisms in freshly filled ponds follows a pattern of succession. For best results, a pond should be stocked at the stage of succession when the size relationship between fish larvae (predators) and zooplankton (prey) is proper. A common practice is to stock larvae 3-7 days after filling. If ponds are filled too long before larvae are stocked, food relationships between fish and invertebrates can be reversed. Predator control includes biological, chemical, physical, and mechanical methods. Although great progress has been made in the development of dry starter diets, prepared feeds are not yet available for successful large-scale production. This problem is usually overcome by starting larvae with live food or with a mixture of live food and dry feed and by shifting larvae to dry diets as they grow. Live food either is collected from zooplankton ponds or is produced in intensive culture conditions. Systems for larval culture can range from ponds to intensive culture with water recirculation systems. Choice of the best system depends on the local climate, technical, and socio-economic conditions.     

Yields of great scallop, Pecten maximus, larvae in a commercial flow-through rearing system in Norway

Survival, growth and yield of competent great scallop (Pecten maximus) larvae were investigated during a full production season in a commercial hatchery in western Norway. Broodstock were collected from natural scallop beds and 12 groups were induced to spawn during the period December 2002 to July 2003. Larvae were reared on a large scale in 36 flow-through tanks (3500 l) at 17±1 °C and continuously fed a mixture of five algal species produced in an indoor continuous-flow system. Large variations in larval performance between spawning groups and tanks were observed, but the results were as good as earlier results using the batch system and prophylactic addition of chloramphenicol. Growth from days 3–24 averaged 4.8 μm day⁻¹±0.8 (sd) and survival 22.4%±21.8 (sd). Mean yield of day 3 larvae was 7.1%±10.0 (sd) and 26.6%±25.9 (sd) for those surviving to day 24. Yield was significantly correlated to larval survival. Larval success was related to initial larval density, algal concentration and season. It was found that the best production regime had an initial larval density lower than 6 ml⁻¹ and algal concentration of less than 12 μl⁻¹ regardless of season. Seventeen tanks met these criteria and produced a mean yield of 0.5 larvae ml⁻¹ to settlement. Flow-through systems are currently regarded as the only feasible method for viable hatchery production of P. maximus larvae in Norway.     

不同饵料对中华绒螯蟹幼体发育和存活的影响

采用高度不饱和脂肪酸（ＨＵＦＡ）营养强化的轮虫、轮虫与卤虫组织投喂中华绒螯蟹幼体,以各项幼体的存活率为评判指标,对不同饵料及其组合的投喂效果进行了探讨。研究结果表明：轮虫是中华绒螯解早期幼体（Ⅰ、Ⅱ期）的适口饵料,幼体存活率随轮虫密度的增加而逐渐上升,但当轮虫数量超过最适密度时,幼体存活率反而有所下降。其中,未强化的轮虫达投喂密度为６０ｉｎｄ．ｍＬ＾－１,强化轮虫最适密度为４０ｉｎｄ．ｍＬ＾－１。Ｚａｏ状Ⅰ、Ⅱ期投喂４０ｉｎｄ．ｍＬ＾－１轮虫,从Ⅲ期开始投喂１０ｉｎｇ．ｍＬ＾－１卤虫无节幼体,能较好地满足中华绒螯蟹幼体发育的营养需求,提高大眼幼体的存活率。表明强化幼体饵料ＨＵＦＡ特别是ＥＰＡ和ＤＨＡ能有效地促进幼体的发育与存活和脱壳率。     

Effect of water recirculation rate and initial stocking densities on competent larvae and survival of the Pacific oyster Crassostrea gigas in a recirculation aquaculture system

The present study evaluated the effect of initial stocking density and water recirculation rate on larval yield (percent of initially stocked larvae alive at the end of the experiment) and production of competent larvae (percent of initially stocked larvae alive at the end of the experiment retained on a sieve with mesh size 239 μm) of Crassostrea gigas in a recirculation aquaculture system (RAS). Different initial larval stocking densities (80, 160 and 320 larvae mL^?1) and water flow rates (100, 200 and 300 mL min^?1, totalling renewal rates of 60, 120 and 180 times day^?1 of water volume in culture tanks, respectively) were evaluated in 2.4-L tanks using a completely randomized design in a factorial scheme. The physicochemical parameters of the water (temperature, salinity, pH, dissolved oxygen and conductivity) were stable in all treatments during the experimental period. Our results demonstrated that the production of C. gigas larvae was feasible at the proposed densities. However, the water renewal rate affected both yield and competent larvae in the recirculation aquaculture system. Oyster cultures with densities of 160 larvae mL^?1 and flow of water of 300 mL min^?1 showed the best yield (89.34 ± 18.43%) and rate of competent larvae (84.09 ± 16.38%) and are therefore recommended with the aim of optimizing larvae cultivation.