Bivalve hatchery technology: The current situation for the Pacific oyster Crassostrea gigas and the scallop Pecten maximus in France

The French oyster farming industry relies almost exclusively on juveniles collected from the natural environment; the supply of spat produced by hatcheries is low, about 10 % of the industry's requirements. Development through selective breeding of oyster stocks which are better suited for aquaculture purposes, is likely to reverse this tendency since only hatcheries will be able to supply such animals. Scallop farming, which at present is poorly developed in France, relies exclusively on hatchery produced spat. Although hatchery technology is constantly being improved, significant production problems remain which must be solved before hatcheries become a major supplier of juveniles for the industry. This paper describes the present state of hatchery technology in France based on experimental results obtained with the great scallop Pecten maximus and the Pacific oyster Crassostrea gigas, over the past ten years. Compared to the great scallop, the Pacific oyster has higher D larva yields (60 % for C. gigas vs. 30 % for P. maximus) and a faster larval growth rate (10 μm·d⁻¹ for C. gigas vs. 5 μm·d⁻¹ for P. maximus). However, Pacific oysters have a greater heterogeneity during larval development and higher mortality rates (40 % for C. gigas vs. 25 % for P. maximus) which produce lower overall yields of pediveliger larvae ready-to-set for Pacific oysters (15 %) compared to the great scallop (30 %). Development of continuous larval and post-larval culture methods along with development of continuous phytoplankton technology offers one of the most promising methods to improve molluscan hatchery techniques.     

Growth and survival of seed oysters in outdoor pumped upwelling systems supplied with fertilized sea water

Hatchery-reared Crassostrea gigas and Ostrea edulis weighing between 0.001 and 11.1 g were grown in outdoor pumped upwelling systems supplied either with natural sea water or with sea water enriched with chemical fertilizers. The effect of water flow rate within the range of 10 to 50 ml min⁻¹ g⁻¹ was also tested with small spat (0.004–0.013 g). Growth rate of small spat and condition index and carbohydrate content of the flesh of all sizes tested was generally enhanced in fertilized water. Optimum growth occurred at flow rates of 20–30 ml min⁻¹ g⁻¹ in fertilized water and 30–50 ml min⁻¹ g⁻¹ in unfertilized water. Once planted in the sea, spat grown in fertilized water showed no evidence of faster growth or better survival than spat growth in unfertilized water.     

Panagrellus redivivus (Linné) as a live food organism in the early rearing of the catfish Synodontis petricola (Matthes)

The nematode Panagrellus redivivus (Linné) has been suggested as a source of live food in the rearing of larval fish and shrimp species. This study tested the use of P. redivivus in the early rearing of the bottom‐feeding catfish Synodontis petricola (Matthes). A comparison of feeding rates of 5000–10 000 nematodes larva⁻¹ day⁻¹ showed that fish receiving 5000 nematodes larva⁻¹ day⁻¹ grew faster than those fed a dry diet, but slower than treatments fed 200 and 600 Artemia larva⁻¹ day⁻¹. Enrichment of nematodes with SuperSelco^® improved fish growth relative to a non‐enriched control treatment, with both treatments receiving 5000 nematodes larva⁻¹ day⁻¹. In the first two trials, feeding commenced 2 days after hatching. In the third study, fish were fed nematodes 6 days after hatching and there was no difference in growth between Artemia‐fed fish (600 Artemia larva⁻¹ day⁻¹) and fish fed 5000 nematodes larva⁻¹ day⁻¹. Thus, it is suggested to feed S. petricola at a nematode density of at least 10 000nematodes larva⁻¹ day⁻¹ in order to achieve growth comparable to that of fish fed Artemia, or, alternatively, to feed 5000 nematodes larva⁻¹ day⁻¹ to improve growth relative to that achieved with a dry diet. Furthermore, nematodes may be enriched with essential fatty acids to improve the growth of S. petricola larvae.     

Predation and energetics of Penaeus indicus (Decapoda: Penaeidae) larvae feeding on Brachionus plicatilis and Artemia nauplii

Brachionus plicatilis and Artemia nauplii were fed to a number of larval stages of the penaeid prawn Penaeus indicus to determine ingestion rates, larval energy requirements and to establish at which stage larval predation commenced. The raptorial feeding rates were then contrasted on an energy basis with filter feeding rates for P. indicus larvae to compare the relative efficiency of these two feeding mechanisms. Brachionus was first eaten as early as protozoea 1 to protozoea 2, while the maximum ingestion rate of 300 rotifers larva^?1 d^?1 (1.06 J larva^?1 d^?1) was obtained during protozoea 3 to mysis 1. Artemia were effectively ingested by P. indicus protozoea 3 (4.1 J larva^?1 d^?1) to post-larva (8.2 J larva^?1 d^?1). Daily energy intake rate from filter feeding increased from 1.1 J larva^?1 d^?1 during protozoea 1 to reach a peak of 5.32 J larva^?1 d^?1 during mysis 3 after which it declined to 2.66 J larva^?1 d^?1 during the post-larval stage. This decline in energy intake from filter feeding with a concomitant increase in energy intake from Artemia predation demonstrates a predominant feeding mode changeover point during mysis 3. Energy intake was consistently low with Brachionus, indicating that it may be unnecessary for commercial culture purposes.     

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.     

Effect of dietary astaxanthin and vitamin A on the reproductive performance of Penaeus monodon broodstock

The reproductive performance of pond tiger shrimp given astaxanthin (100 mg·kg⁻¹) and/or vitamin A (20 000 IU·kg⁻¹) for 61 d in tanks was assessed in a 2 × 2 factorial experiment in a completely randomized design. Tissue carotenoid (total carotenoid; astaxanthin free form, AF; monoester, AM; diester, AD) was analyzed using high performance liquid chromatography. The gonad index (GI) of shrimps fed diets with astaxanthin and/or vitamin A (3.05 ± 0.11 to 3.30 ±0.17) were significantly higher than shrimps not fed any supplement (2.24 ± 0.17). A significant interaction between astaxanthin and vitamin A for ovarian development and spawning was detected (GI, 3.18 ± 0.14). The ovarian total carotenoid (10.85 ± 1.52 μg·g⁻¹) and astaxanthin (AF, 7.65 ± 1.43 μg·g⁻¹; AM, 0.63 ± 0.12 μg·g⁻¹) content of shrimps fed a diet with astaxanthin supplement were significantly higher than those without. In shrimps fed diets with and without vitamin A, no differences in ovarian total carotenoid (9.38 ± 0.58 μg·g⁻¹) and AF (8.12 ± 1.55 μg·g⁻¹) content were observed except for AM (0.64 ± 0.15 μg·g⁻¹) content. In contrast, the ovarian AD level was significantly higher (1.14 ± 0.3 μg·g⁻¹) in shrimps fed diets with both supplements compared to other diets. A significant interaction between astaxanthin and vitamin A was detected for AD storage. In the hepatopancreas of shrimps fed diets with or without astaxanthin or vitamin A, no significant differences in AF and AM content was observed. On the other hand, the AD (4.92 ± 1.3 μg·g⁻¹) level in the hepatopancreas of shrimps fed diet with vitamin A was significantly higher than those without. These results suggest the involvement of astaxanthin in P. monodon reproduction and its need for inclusion in broodstock diets. Supplementation of vitamin A to broodstock diet of P. monodon appears to enhance its ovarian development and spawning.     

Comparative growth and survival of spat of the Caribbean pearl oyster,Pinctada imbricata cultivated indoor with microalgae diets and outdoor with natural diet

We report the results of survival and growth in size and dry mass of spat of the Caribbean pearl oyster Pinctada imbricata cultivated under outdoor (field culture) and indoor (Laboratory) conditions. Field group fed on environmental seston. Laboratory groups were fed with mono, binary and ternary mixtures of three cultivated algae: Isochrysis galbana (Ig), Tetraselmis chuii (Ig) and the Chaetoceros sp. (Ch‐A, isolated from north‐eastern Venezuela). After 30 days of trial, fatty acid profiles of spat were determined along with growth in length and height shell, adductor muscle and soft tissue dry mass. During the field grow‐out phase (field culture), samplings were performed at days 1, 15 and 30 to measure environmental variables of phytoplankton biomass (chlorophyll a), dissolved oxygen, seston, temperature and salinity. A significant increase in size and soft tissue mass occurred in spat fed the diets including the tropical diatom (Chaetoceros sp.). In contrast, monoalgal diets of Tc and Ig yielded no significant differences in size and mass of spat, compared with the field culture. These results suggest that nutritional requirements of cultivated spat for specific fatty acids of physiological importance for marine bivalves, such as: 16:0, 16:1n‐7, 18:2n‐6, 20:4n‐6, 18:3n‐3 and 20:5n‐3, were satisfied from microalgal diets with Ch‐A, alone or in combination, compared with spat fed from the field culture.     

Effect of increased water recirculation rate on algal supply and post-larval performance of scallop (Pecten maximus) reared in a partial open and continuous feeding system

In a commercial scallop hatchery spat production depends on a culture system which ensures high survival and good growth. Reuse of water with algae may increase the food exploitation and hence reduce the costs. Post-larvae of great scallop (Pecten maximus) were studied in a commercial hatchery using a partial open and continuous feeding tank system. Three different water recirculation rates (67, 83 and 92%) were tried out in two experiments with post-larvae originating from three spawning groups of ages between 43 and 57 days post-spawn, 316–886 μm shell-height and 1.1–9.6 μg ash-free dry weight. The post-larvae were held in sieves in tanks of 2500 l where a downwelling flow was maintained by airlifts. New water with a mix of monocultured algae was continuously added to the tanks at algal concentrations of 10 and 15 cells μl⁻¹ in experiment 1 (groups 1 and 2) and 2 (group 3), respectively. The algal supply to each sieve was reduced along with increased recirculation rate, but was kept between 6 and 13 cells μl⁻¹. Generally no significant differences in survival, growth or chemical content were found between the three recirculation rates, while few differences were found between and within groups. Large variation in survival was found between and within groups (1–81%). Highest survival was found in experiment 1, and where post-larvae from two settlements were used, the first settlement survived better than the second. The daily growth ranged from 15 to 62 μm shell-height and from 0.3 to 2.6 μg ash-free dry weight. The scallop post-larvae could well be reared at all three recirculation rates studied as an increase from 67 to 92% did not seem to affect the post-larval performance seriously. The algal supply, however, had to be compensated by an increasing number of cells (>10 cells μl⁻¹) when increasing the recirculation rate.     

Use of a probiotic for the culture of larvae of the Pacific oyster (Crassostrea gigas Thunberg)

Additions of bacteria (strain CA2) as a food supplement to xenic larval cultures of the oyster Crassostrea gigas consistently enhanced growth of larvae during different seasons of the year. Bacterial enhancement of larval growth occurred when either Isochrysis galbana (ISO), I. aff. galbana (T-ISO) or Pseudoisochrysis paradoxa (VA-12) were used as algal foods. Additions of CA2 bacteria at 10⁵ cells ml⁻¹ to cultures of algal-fed larvae increased larval growth, the proportion of larvae that set to produce spat, and the subsequent size of spat. A lower proportion of slow-growing larvae in populations receiving additions of CA2 bacteria compared with populations of larvae fed only algae, suggests a bacterial nutritional contribution to larval growth. Manipulation of bacterial populations present in bivalve larval cultures is a potentially useful strategy for the enhancement of oyster production.     

Dietary calcium requirements of juvenile tilapia, Oreochromis niloticus × O. aureus, reared in fresh water

A feeding experiment was conducted to determine the dietary calcium (Ca) requirement for juvenile hybrid tilapia, Oreochromis niloticus × O. aureus reared in nature water. Purified diet supplemented with 0, 1, 2, 3, 4, 5, 7 and 10 g Ca kg⁻¹ diet providing of 0.6, 1.6, 2.6, 3.7, 4.7, 5.5, 7.5 and 10.7 g Ca kg⁻¹ diet, respectively, were fed to tilapia (mean initial weight: 0.52 ± 0.01 g, n = 3) for 8 weeks. Each diet was fed to three replicate groups of fish in a closed, recirculating fresh water rearing system. The rearing water contained 27.1–33.3 mg L⁻¹ Ca. The tilapia fed the diets supplemented with ≥3.7 g Ca kg⁻¹ had significantly (P < 0.05) higher weight gain, when compared with fish fed the diet with ≤1.6 g Ca kg⁻¹. Fish fed the unsupplemented control showed significantly lower weight gain when compared with the other groups (P < 0.05). Bone Ca concentration was highest in fish fed the diets with ≥4.7 g Ca kg⁻¹, intermediate in fish fed the diet with 2.6 g Ca kg⁻¹ and lowest in fish fed the control diet. Scale Ca concentration was higher in fish fed the diets with ≥3.7 g Ca kg⁻¹ than in fish fed the diets with ≤2.6 g Ca kg⁻¹. Serum alkaline phosphatase activity was 36% increased in fish fed the diets with ≥2.6 g Ca kg⁻¹ than fish fed the diets with <1.6 g Ca kg⁻¹. Analysis by broken‐line regression of weight gain, bone and scale Ca concentrations indicated that the adequate dietary Ca concentration for tilapia in water containing 27.1–33.3 mg Ca L⁻¹ was 3.5, 4.3 and 4.2 g Ca kg⁻¹ diet, respectively, supplied as Ca‐lactate.     

Effect of varying dietary energy level on feed intake, feed conversion, whole-body composition and growth of Malawian tilapia, Oreochromis shiranus– Boulenger

Four isonitrogenous [30% crude protein (CP)] diets containing different gross energy levels (13.39, 16.74, 20.50 and 23.85 kJ g⁻¹) were evaluated to determine the optimum energy for the Malawian tilapia Oreochromis shiranus. Each tank (120 L) was stocked with 18 juvenile tilapia (average weight 7.32±0.25 g) and they were fed the experimental diets for 10 weeks. The final average weight of the fish was approximately twofold higher (range: 12.64–16.77 g) than the initial weight. The dietary energy significantly (P<0.05) influenced growth. The average weight of fish fed dietary energy level 20.50 kJ g⁻¹ was significantly higher (P<0.05) than the weight of the fish fed any of the other experimental diets. There was no significant difference in growth of fish fed 13.39 and 16.74 kJ g⁻¹ energy levels, but 23.85 kJ g⁻¹ produced the lowest growth rates. There were no significant differences (P>0.05) between feed intake across the treatments. Feed conversion ratio (range: 2.2–3.0) and protein efficiency ratio (range: 1.10–1.50) among the dietary treatment groups were in agreement with trends for weight gain. Dietary energy level significantly (P<0.05) influenced the body composition of O. shiranus. Whole‐body moisture (range: 64.27–67.15%) and ash (range: 13.21–14.73%) decreased in all treatments. Whole‐body protein (range: 63.57–66.16%) increased only in groups fed on the diet containing 20.50 kJ g⁻¹. Whole‐body fat (range: 13.58–17.27%) and gross energy (range: 28.411–33.210 kJ g⁻¹) increased significantly (P<0.05). Fish survival was 100% in all treatments. The results demonstrated that to maximize growth at a temperature of 23°C, O. shiranus should be fed diets containing 20.50 kJ g⁻¹ gross energy.     

Purified deoxynivalenol or feed restriction reduces mortality in rainbow trout,Oncorhynchus mykiss (Walbaum), with experimental bacterial coldwater disease but biologically relevant concentrations of deoxynivalenol do not impair the growth of Flavobacterium psychrophilum

Diets containing deoxynivalenol (DON) were fed to rainbow trout Oncorhynchus mykiss (Walbaum) for 4 weeks followed by experimental infection (intraperitoneal) with Flavobacterium psychrophilum (4.1 × 10⁶ colony‐forming units [CFU] mL⁻¹). Mortality of rainbow trout fed either 6.4 mg kg⁻¹ DON or trout pair‐fed the control diet was significantly reduced (P < 0.05) in comparison with trout fed the control diet to apparent satiation (<0.1 mg kg⁻¹ DON). In a second experiment, trout were fed one of three experimental diets; a control diet, a diet produced with corn naturally contaminated with DON (3.3 mg kg⁻¹ DON) or a diet containing purified DON (3.8 mg kg⁻¹); however, these fish were not experimentally infected. The presence of DON resulted in significant reduction (P < 0.0001) in feed intake as well as weight gain after 4 weeks. Respiratory burst of head‐kidney leucocytes isolated from rainbow trout fed diets containing purified DON (3.8 mg kg⁻¹) was significantly higher (P < 0.05) at 35 day post‐exposure compared with controls. The antimicrobial activity of DON was examined by subjecting F. psychrophilum in vitro to serial dilutions of the chemical. Complete inhibition occurred at a concentration of 75 mg L⁻¹ DON, but no effect was observed below this concentration (0–30 mg L⁻¹).     

Effect of prebiotic konjac mannanoligosaccharide on growth performances,intestinal microflora,and digestive enzyme activities in yellow catfish,Pelteobagrus fulvidraco

In the present study, konjac mannanoligosaccharide (KMOS) was evaluated as a prebiotic in yellow catfish. The fish were fed with diets containing KMOS in four concentrations: 0 g kg^?1 (C), 1.0 g kg^?1 (KM1), 2.0 g kg^?1 (KM2), and 3.0 g kg^?1 (KM3) for 49 days, respectively. Another group fed with diets containing 3.0 g kg^?1 yeast cell wall mannanoligosaccharide (MOS) (M3) was set as positive control. The results indicated that fish receiving the diets supplemented with KMOS or MOS showed higher relative gain rate (RGR), specific growth rate (SGR), and lower feed conversion ratio (FCR) with significantly differences (P < 0.05) than those fed with the basal diets. Moreover, fish receiving the diets with 2.0 g kg^?1 KMOS inclusion showed higher RGR, SGR, and lower FCR (P < 0.05) than that feeding the diets supplemented with 3.0 g kg^?1 MOS. The quantities of Bifidobacterium spp. were significantly increased (P < 0.05). Meanwhile, Escherichia coli and Aeromonas spp. were significantly reduced (P < 0.05) in the fish-feeding diets with 2.0 g kg^?1 KMOS supplement. Compared with the control group, the significantly enhancement of protease and amylase activity (P < 0.05) in intestine and pancreas was observed in fish fed with diets containing KMOS or MOS. Collectively, an optimum level of KMOS inclusion in diets could modulate intestinal microflora, induce digestive enzyme activity, and improve the growth performance of yellow catfish significantly.     

Effect of dietary protein and energy levels on growth,oxygen consumption,haemolymph and digestive gland carbohydrates,nitrogen excretion and osmotic pressure of Litopenaeus vannamei (Boone) and L. setiferus (Linne) juveniles (Crustacea,Decapoda; Penaeidae)

The influence of protein and energy levels on growth rate, survival, pre- and post-prandial oxygen consumption, ammonia excretion, haemolymph glucose (HG), glycogen in digestive gland and osmotic pressure (OP) in white shrimp Litopenaeus vannamei (Boone) and L. setiferus (Linne) juveniles was studied. Diets containing a high-quality protein at a protein/energy (P/E) ratio of 16, 26, 31 and 36 mg kJ⁻¹ were fed at 20% of shrimp body weight of two sizes: < 1 g and > 1 g. Both species showed a optimum P/E ratio of 36 mg kJ⁻¹ (33–44% protein and 6–23% carbohydrate) in juveniles < 1 g. For shrimp > 1 g, L. setiferus showed a higher growth rate in the diet with 16 mg kJ⁻¹ (27% protein; 32% carbohydrate) and L. vannamei between 26 and 36 mg kJ⁻¹ (33–44% protein and 6–23% carbohydrate). In both experiments, the growth rate of L. vannamei was 2–3 times that observed in L. setiferus. Routine oxygen consumption and apparent heat increment (AHI) of L. setiferus juveniles was two times higher than that observed in L. vannamei juveniles, which could indicate that L. setiferus has a higher metabolic rate. The O/N ratio varied according to protein level, with higher values (O/N = 180) with a 16-mg kJ⁻¹ diet and lower values (O/N = 73) with a 36-mg kJ⁻¹ diet in L. setiferus juveniles. A similar variation in O/N ratio was obtained in L. vannamei fed with all diets with an interval between 22 and 50. An inverse relation between ammonia excretion and HG, and digestive gland glycogen (DGG) in relation to an increase in the P/E ratio indicate that both shrimp species are well adapted to use carbohydrates and/or proteins from their diet. The higher values of hyper-osmotic capacity (hyper-OC) were observed in L. setiferus < 1 g fed with 36 mg kJ⁻¹ and the lowest in L. vannamei < 1 g fed with 31 mg kJ⁻¹. Intermediate values of hyper-OC were observed in both species fed all diets indicating that osmotic factors of juveniles < 1 g of both species are more affected by the P/E ratio than juveniles > 1 g. All results showed that juveniles > 1 g of both species are less dependent of P/E ratio than juveniles < 1 g. Litopenaeus vannamei is a most tolerant shrimp species with a high capacity to use a wide range of dietary P/E ratios for growth, which may be due to its lower energy requirements. Litopenaeus setiferus showed a lower capacity to accept different P/E ratios but the optimum P/E ratio obtained with this species shows that L. setiferus accept diets with a high carbohydrate level as well. These results demonstrate that there are nutritional and physiological differences that explain the differences that have been observed when both species were cultured in commercial ponds.     

Enhancing the dietary value of palm oil in the presence of lysolecithin in tiger shrimp, <Emphasis Type="Italic">Penaeus monodon</Emphasis>

The effect of four iso-nitrogenous and iso-lipidic diets containing soy lecithin and lysolecithin with fish oil (sardine) and palm oil on growth, digestibility, and fatty acid composition of tail muscle and non-muscle portions of tiger shrimp, Penaeus monodon, was evaluated. Shrimp fed with lysolecithin diets had significantly (P?<?0.05) higher daily growth coefficient values (1.40–1.45% day^?1) than those fed with soylecithin containing diets (1.32–1.37% day^?1). Correspondingly, lysolecithin-supplemented diets showed significantly higher (P?<?0.05) apparent digestibility coefficients (ADC) of fatty acids with both the oils due to higher emulsification ability of small micelle forming by lysolecithin. However, there were no significant differences in survival and FCR among all treatments. The fatty acid composition of the test diets reflected to a certain extent in the fatty acid composition of the muscle and non-muscle portions of shrimp. Arachidonic, eicosapentaenoic, and docosahexaenoic acid contents of muscle and non-muscle portions of shrimp were significantly (P?<?0.05) higher in lysolecithin-supplemented diet compared to soylecithin-supplemented diet. The present results suggest that lysolecithin improved the fatty acid digestibility with its high emulsification properties that reflected in better performance by improving dietary value of palm oil.     

Effect of different diets on growth and digestive enzyme activity in Litopenaeus vannamei (Boone, 1931) early post-larvae

Growth rate, soluble-protein content and digestive-enzyme activities were studied in Litopenaeus vannamei (Boone, 1931) early post-larvae under six feeding regimens, which included combinations of freshly hatched Artemia nauplii, an artificial diet and algae. Growth (0.11 mg DW day⁻¹) and soluble-protein content (61.8 μg protein larvae⁻¹ at PL₁₀) of post-larvae fed mixed diets were significantly higher (P < 0.05). An artificial diet used alone or co-fed with algae caused the lowest growth (0.03–0.05 mg DW day⁻¹) and soluble-protein content (13.7–15.5 μg protein larvae⁻¹ at PL₁₀). Trypsin-like activity was higher (up to 10 times) in post-larvae fed Artemia nauplii and an artificial diet alone or plus algae. The artificial diet stimulated chymotrypsin activity, apparently in response to squid meal present in this diet. Amylase activity increased when post-larvae were fed the artificial diet. This was apparently related more to the origin of the starch than to the total carbohydrate level of the diet. No obvious relationship was found between enzyme activity and growth in any feed combination. Based on growth and soluble-protein content, we determined that partial substitution (50%) of Artemia nauplii by artificial diet and the use of algae co-fed beyond the first post-larval stage benefits growth and the nutritional state of L. vannamei post-larvae.     

Optimum dietary protein and lipid levels for growth of juvenile sea cucumber Apostichopus japonicus

A feeding trial of three protein (200, 300 and 400 g kg⁻¹) and two lipid levels (20 and 100 g kg⁻¹) was conducted to determine the proper dietary protein and lipid levels for growth of juvenile sea cucumber Apostichopus japonicus. Dietary protein and lipid levels were adjusted by adding with different levels of soybean meal, squid liver oil and soybean oil, respectively. Three replicate groups of sea cucumbers (average weight of 1.3 g) were fed the experimental diets for 12 weeks. At the end of the feeding trial, survival was not affected by dietary protein and lipid levels (P > 0.05). Weight gain (WG) and specific growth rate (SGR) of sea cucumbers were significantly affected by dietary protein (P < 0.006) and lipid levels (P < 0.001). The highest WG and SGR were observed in sea cucumbers fed the 200 and 400 g kg⁻¹ protein diet with 20 g kg⁻¹ lipid (P < 0.05). WG and SGR of sea cucumbers fed the diet containing 20 g kg⁻¹ lipid were higher than those of sea cucumbers fed the 100 g kg⁻¹ lipid diets (P < 0.05) at each dietary protein level. Apparent digestibility coefficients of dry matter, crude protein, carbohydrate and gross energy of sea cucumbers fed the 20 g kg⁻¹ lipid diets were significantly higher than those of the 100 g kg⁻¹ lipid diets at 200 and 400 g kg⁻¹ protein (P < 0.05). Moisture, crude protein, crude lipid and ash contents were not significantly different among the groups. The results of this study indicate that the diet containing 200 g kg⁻¹ protein (170 g kg⁻¹ digestible protein) with 20 g kg⁻¹ lipid (13 g kg⁻¹ digestible lipid) may be sufficient for optimum growth of juvenile sea cucumber.     

The optimal dietary level of ascorbic acid for juvenile Pacific bluefin tuna, Thunnus orientalis

A feeding experiment was conducted to evaluate the efficacy of, and determine the requirements for dietary AsA (l-ascorbic acid) using its popular derivative l-ascorbyl-2-monophosphate-Mg (APM) for juvenile Pacific bluefin tuna (PBT). The five test diets (with APM-0, -400, -800, -1200 and -1600) were prepared by adding 0, 400, 800, 1200 and 1600 mg of APM kg diet^?1, respectively. These diets, together with chopped sand lance (the control diet), were administered, in duplicate to 0.27 g PBT at 25 days after hatching (300 juveniles per 15 m³ tank). The PBT were fed to apparent satiety 6 times a day for 2 weeks. While final body weight, feed conversion and survival showed no differences among diets APM 400–1600, PBT fed APM-0 indicated lower growth performance together with anorexia, dark pigmentation and ataxia from 5 days and reached 80 % mortality at 12 days after the start of the feeding trial. In addition, liver and brain ascorbic acid (AsA) concentrations increased with increasing dietary APM levels, the values were similar in PBT fed diets with APM-1200 and APM-1600, and liver and brain concentrations of AsA were significantly higher in these fish than in the PBT fed the other diets (P < 0.05). The PBT responded to increasing dietary APM, and the fish fed APM-1200 had the highest weight gain, protein and lipid content. The data indicate that PBT can utilize APM as an AsA source and suggest that dietary supplementation with APM-1200 (454 mg AsA kg^?1 diet) would result in satisfactory growth.     

Influence of different diets on the growth,survival, fecundity and proximate composition of brine shrimp Artemia franciscana (Kellog, 1906)

Artemia franciscana was studied under in vitro conditions, and fed with five different microalgae species, two organic diets and one mixed diet to evaluate the nutritional profile and growth performance. The A. franciscana instar‐I nauplii were stocked at a density of 100 per litre of ground borewell water with a salinity of 70 ppt in a plastic container and the culture continued for 12 days. The A. franciscana was fed with five microalgal species, such as Tetraselmis sp., Chaetoceros sp., Isochrysis sp., Thalassiosira sp. and Nannochloropsis sp., and organic diets of rice bran, soybean meal, and a mixture of Tetraselmis sp. and Chaetoceros sp. with rice bran, giving a total of eight experiments. The growth of A. franciscana was measured by length, and was observed to be the greatest (10,850 μm) in the group that was fed the mixed algae combination, and the lowest (7,290 μm) in the group that was fed Nannochloropsis sp. Among the different treatments, the highest survival value of 76% was seen in the group that was fed Chaetoceros sp. The fecundity was higher in A. franciscana that were fed with algae Chaetoceros sp., while the lower rate was observed with the group that was fed Nannochloropsis sp. Analysis of proximate composition showed increased levels in the animals fed with Chaetoceros sp. (lipid, 19.40%; eicosapentaenoic acid, 6.70 mg; docosahexaenoic acid, 10.20 mg; amino acids: proline, 2.06 μg; histidine, 0.77 μg, arginine, 0.65 μg, glycine, 0.80 μg, glutamic acid, 1.75 μg; threonine, 1.42 μg) and the mixed diet (protein, 58.59%; carbohydrate, 21.30%; amino acids: asparagine, 0.90 μg; serine, 1.65 μg; tryptophan, 1.66 μg; leucine, 1.50 μg; phenylalanine, 1.14 μg; valine, 0.66 μg). All components showed the lowest level in the diet fed with Tetraselmis species. These A. franciscana populations showed better survival, higher fecundity and biochemical profiles when cultured with microalgae Chaetoceros sp. These data are useful to improve A. franciscana culture in aquaculture to produce quality cysts and biomass, especially in feeding larvae of marine species.     

Nursery growth, survival and chemical composition of great scallop Pecten maximus (L.) spat from different larval settlement groups

Scallop Pecten maximus spat (1.3–2.1 mm shell height) from different settlement groups were transferred from hatchery to land‐based nursery at different ages and sizes. Chemical content, growth and survival were compared at transfer time and after 1 and 8 weeks of nursery growth. Growth was lowest and mortality highest in the first week after transfer. Mean shell height growth was 21.5–71.4 μm day^?1 and ash‐free dry weight (AFDW) growth ?2.7 to 10.3 μg day^?1. Spat from the first settlement group attained a larger size and weight than spat from larvae settled 3 days later, but had a lower daily growth rate (%). Keeping the late‐settled spat a longer time in the hatchery to reach a bigger size before transfer seemed not to improve subsequent nursery growth. Survival showed a large variation with mean survival ranging from 32% to 74%. A substantial reduction in lipid content was found after transfer to the nursery. Sterol content at transfer was the only lipid class correlating with survival in the nursery. Based on the results, it is justified that spat groups of different settlement age are included in production of 15‐mm great scallop spat if they are transferred from the hatchery at the same age.