Effects of daphnia (Moina micrura) plus chlorella (Chlorella pyrenoidosa) or microparticle diets on growth and survival of larval loach (Misgurnus anguillicaudatus)

Culture performance beyond metamorphosis of larval loach (Misgurnus anguillicaudatus) was examined in a feeding experiment of the early development stage (20 days after hatch; DAH). Total length, dry weight, length- and weight-specific growth rate (SGR) and survival were monitored in different diet regimes. During 20 days, diet treatments included: microparticle diets (A); live daphnia (Moina micrura) (B); live daphnia plus live chlorella (Chlorella pyrenoidosa) (C); and live daphnia plus microparticle diets (D). Fish survival rates during 20 days were 21.23 ± 4.2% (A), 73.19 ± 2.8% (B), 90.76 ± 3% (C) and 91.46 ± 3.1% (D), respectively. Length- and weight-specific growth rate after 20 DAH (final mean SGR; % day⁻¹) were 5.36 ± 0.44 and 15.75 ± 1.52 (A), 9.29 ± 1.25 and 23.47 ± 2.23 (B), 9.42 ± 1.55 and 24.88 ± 2.9 (C) and 9.55 ± 1.23 and 24.40 ± 2.75 (D), respectively. Fish in treatments B, C and D displayed higher growth rates and were significantly longer and heavier than fish in treatment A by the end of the experiment (Ρ < 0.05). Fish in treatment A had highly significant greater (Ρ < 0.001) mortalities than in treatments B, C and D. There were no significant differences in any growth parameter between fish in treatments B, C and D, but the survivals in treatments C and D (90.76% and 91.46%) were significantly higher than in treatment B (73.19%, Ρ < 0.05). The results demonstrated that enriched prey and co-feeding may serve as a potential feeding strategy for loach larvae, and the form of co-feeding reduces the costs and dependence on live foods to a certain extent. We concluded that larval loach should be reared over metamorphosis using either of the following methods: feed with live daphnia supplemented with microparticle diets or with live chlorella. However, a prolonged rearing period of loach larvae is needed to detect nutritional problems and observe remote effects of co-feeding on weaning in the future.     

Natural carbon stable isotope ratios as indicators of the relative contribution of live and inert diets to growth in larval Senegalese sole (Solea senegalensis)

The relative contributions of live Artemia metanauplii and an inert diet for growth of Senegalese sole larvae and postlarvae were assessed through the analysis of carbon stable isotopes ratios (δ¹³C) in both diets and whole larval tissue. Larvae were reared on four dietary regimes: 100% live prey (rotifers and Artemia), 100% inert formulated diet and two co-feeding regimes of 70:30 and 30:70 ratios of Artemia and inert diet, respectively. Larvae from the live food regime and both co-feeding regimes showed a steep increase in δ¹³C from 10 days after hatching (DAH) as a result of the onset and continuation of Artemia consumption. From 12 DAH fish larvae from all the regimes showed significant isotopic differences as their δ¹³C increased to final asymptotic values of − 15.1, − 15.6 and − 16.3‰ in the live food, 70:30 and 30:70 regimes, respectively. Carbon turnover rates in larvae from both live food and co-feeding regimes were relatively high (0.071 to 0.116 d^− 1) but more than 90% of the observed change in fish tissue isotopic values was accounted for by the retention of carbon in new tissue growth. A two-source, one-isotope mixing model was applied to estimate the nutritional contribution of Artemia and inert diet to postlarvae growth in the co-feeding regimes. At 23 DAH, the relative contribution of live and inert diets to tissue growth in larvae was respectively, 88 and 12% for the 70:30 co-feeding regime and 73 and 27% for the 30:70 co-feeding regime. At 17 DAH, the estimated proportion of tissue carbon derived from the inert diet was higher at 23 and 38% for the 70:30 and 30:70 regimes, respectively. The results suggest that co-feeding regimes in Solea senegalensis larvae may be adjusted to meet ontogenetic changes in the capacity for larvae to utilise inert diets. The contrasting levels of carbon isotope discrimination between diet and tissue in larvae reared on either 100% live feed or 100% inert diet indicate relatively poor utilization of nutrients from the inert diet. The use of isotopic discrimination factors as potential indicators of the digestive physiological performance of a consuming organism in regards to its diet is discussed.     

Co-feeding of live feed and inert diet from first-feeding affects Artemia lipid digestibility and retention in Senegalese sole (Solea senegalensis) larvae

The present study intended to evaluate the effects of early introduction of inert diet in lipid digestibility and metabolism of sole, while larval feed intake, growth and survival were also monitored. Solea senegalensis larvae were reared on a standard live feed regime (ST) and co-feeding regime with inert diet (Art R). Trials using sole larvae fed with Artemia enriched with two different lipid emulsions, containing glycerol tri [1-¹⁴C] oleate (TAG) and L-3-phosphatidylcholine-1,2-di-[1-¹⁴C] oleoyl (PL), were performed at 9 and 17 days after hatching (DAH) to study lipid utilization. Co-feeding did not affect sole survival rates (ST 59.1 ± 15.9%; Art R 69.56 ± 9.3%), but was reflected in significantly smaller final weight at 16 DAH (ST 0.71 ± 0.20; Art R 0.48 ± 0.14 mg). Higher feed intake was observed in sole larvae fed on Artemia enriched with labeled PL at 9 DAH but not at 17 DAH. At 17 DAH, the smaller larvae (Art R treatment) ingested proportionally more Artemia in weight percentage, independently of enrichment. At 9 DAH lipid digestibility was equal among treatments and higher than 90%, while at 17 DAH it was higher in ST treatment (around 73%) compared to the Art R group (around 66%). Lipid retention efficiency at 9 DAH was higher in the Art R treatment, reaching values of 50%, while these values almost duplicated at 17 DAH, ranging up to 80% in both treatments without significant differences. These results show that co-feeding of live feed and inert diet from first-feeding in Senegalese sole has a toll in terms of growth and lipid digestibility but does not seem to compromise lipid metabolic utilization.     

Effects of early weaning strategies on growth,survival and digestive enzyme activities in cobia (<Emphasis Type="Italic">Rachycentron canadum</Emphasis> L.) larvae

The effects of weaning strategies of cobia (Rachycentron canadum L.) larvae to commercial microdiets, either from rotifers or from Artemia, on growth, survival and enzymatic digestive capacity, were investigated. In the first experiment, cobia larvae were weaned from rotifers by co-feeding with a microdiet (Otohime) from 8, 13 or 20 days post-hatching (dph). The larvae in the control treatment were fed rotifers (2–12 dph), Artemia nauplii from 7 dph, and co-fed with the microdiet from 20 dph. In the second experiment, the larvae were weaned from Artemia, which was fed to the larvae from 7 dph, by co-feeding with a microdiet (NRD) from 8, 13 or 18 dph. The larvae in control treatment were fed rotifers, then Artemia to the end of the experiment (28 dph). Weaning of cobia larvae onto a microdiet directly from rotifers significantly reduced growth, survival and digestive capacity of the larvae and did not lead to larval acceptance of the microdiet, compared to those weaned from Artemia in the first experiment. Early weaning of cobia larvae onto NRD microdiet (on 8 or 13 dph) from Artemia in the second experiment also reduced growth, survival rate and gut maturation index, compared to those fed live feed. With available microdiets, weaning of cobia larvae could start from Artemia at around 18 dph in order to obtain comparable growth, survival and gut maturation to larvae fed live feed.     

Effect of stocking density on survival and growth performance of pikeperch, <Emphasis Type="Italic">Sander lucioperca</Emphasis> (L.), larvae under controlled conditions

The effect of stocking density on the survival and growth of pikeperch, Sander lucioperca (L.), larvae was examined in two consecutive experiments. In experiment I, 4-day-old larvae [body wet weight (BW): 0.5 mg; total body length (TL): 5.6 mm] were reared in 200-l cylindro-conical tanks in a closed, recirculating system (20 ± 0.5°C) at three stocking densities (25, 50 and 100 larvae l⁻¹) and fed a mixed feed (Artemia nauplii and Lansy A2 artificial feed) for 14 consecutive days. At densities of 25 and 100 larvae l⁻¹, growth rate and survival ranged from 2.7 to 1.9 mg day⁻¹ and from 79.2 to 72.3%, and fish biomass gain ranged from 0.6 to 2.0 g l⁻¹, respectively. There were two periods of increased larval mortality: the first was at beginning of exogenous feeding and the second during swim bladder inflation. In experiment II, 18-day-old larvae (BW: 35 mg; TL: 15.6 mm) obtained from experiment I were reared under culture conditions similar to those of experiment I, but at lower stocking densities (6, 10 and 15 larvae l⁻¹). The fish were fed exclusively with artificial feed (trout starter) for 21 consecutive days. At densities of 6 and 15 larvae l⁻¹, the growth rate and fish biomass gain ranged from 28.8 to 23.1 mg day⁻¹ and from 2.0 to 3.3 g l⁻¹, respectively. The highest survival (56.5%) was achieved at a density of 6 larvae l⁻¹. Mortality at all densities was mainly caused by cannibalism II type behaviour (27–35% of total). In both experiments, growth and survival were negatively correlated and fish biomass gain positively correlated with stocking densities. The present study suggests that the initial stocking density of pikeperch larvae reared in a recirculating system can be 100 individuals l⁻¹ for the 4- to 18-day period post-hatch and 15 individuals l⁻¹ for the post-19-day period.     

Use of the freshwater rotifer <Emphasis Type="Italic">Brachionus angularis</Emphasis> as the first food for larvae of the Siamese fighting fish <Emphasis Type="Italic">Betta splendens</Emphasis>

Larvae of the Siamese fighting fish Betta splendens were reared on the mass-cultured small freshwater rotifer Brachionus angularis Laos strain (UTAC-Lao), Paramecia sp., and Artemia as live food sources. Larvae fed live food were found to have a significantly high survival rate (97.5–100%) 18 days after hatch (DAH) in comparison to the control unfed larvae, which died by 12 DAH. Rotifer-fed larvae were found to grow faster than paramecia-fed larvae. The fastest growth rate was observed in larvae fed a combination of rotifer and Artemia, with growth in these larvae increasing by 282% by 18 DAH [total length (TL) 11.3 ± 1.2 mm] relative to body measurements taken 3 DAH. The next fastest growth rate was observed in rotifer-fed larvae, with a 158% increase in growth observed by 18 DAH (TL 7.6 ± 0.5 mm). The paramecia-fed larvae were found to grow by only 54.3% (TL 4.6 ± 0.1 mm) during the same period.     

Tench (<Emphasis Type="Italic">Tinca tinca</Emphasis> L.) larvae rearing under controlled conditions: density and basic supply of <Emphasis Type="Italic">Artemia</Emphasis> nauplii as the sole food

After artificial reproduction of tench, larvae must be maintained indoors, and studies on rearing conditions are needed, focussing on the reduction of labour and costs. Three experiments on larvae (5th day post-hatch) were conducted for 25 days using Artemia nauplii as the sole food in order to determine basic feeding and density conditions during the first rearing period. Tench were maintained in 25 l fibreglass tanks, supplied with an artesian water flow throughout of 0.2 l min⁻¹. Water temperature was 22.5 ± 1°C, and the photoperiod was natural. Larvae fed on a restricted amount of nauplii reached high survival rates, even with the minimum of 50 nauplii larva⁻¹ day⁻¹. This amount of food may be sufficient at least for the first 25 days of exogenous feeding if fast growth is not the priority, and high densities can be maintained with good survival rates (over 90% up to 160 larvae l⁻¹ and 77% with 320 larvae l⁻¹). When food was supplied in excess once a day, high survival rates were achieved (91–97%), without differences among the densities tested. Animals at a density of 100 l⁻¹ reached the highest length (15.57 mm) and individual weight (46.8 mg). This growth is greater than those reported in studies feeding several times a day. It could be deduced that, while live food remains available for tench, it is not necessary to feed so frequently. Considering the relationship among the initial number of animals, final survival and growth and ration supplied, the new data reported here are useful to establish suitable stocking densities under both culture and experimental conditions.     

Organogenesis of exocrine pancreas in sharpsnout sea bream (<Emphasis Type="Italic">Diplodus puntazzo</Emphasis>) larvae: characterization of trypsin expression

The ontogeny and differentiation stages of digestive systems related with trypsin expression in larvae of sharpsnout sea bream, Diplodus puntazzo, were investigated from hatching to 40 DAH (days after hatching), and total lengths and weights of larvae were determined. Histologic and enzymatic techniques were used to explain the functional development of the pancreas including trypsin activity. The pancreas was identified as a compact structure located in the region slightly posterior to the liver. At 3 DAH, first anus and then mouth opened. Incipient pancreas secretion polyhedral cells could be first observed as zymogen granules. During larval metamorphosis, the pancreas became diffuse, spreading throughout the mesentery in proximity to the stomach, the anterior intestine and the pyloric caeca. The specific activity of trypsin (42.54 ± 6.8 mU/mg protein⁻¹) was found as early as after hatching at larvae size of 2.87 ± 0.34 mm at 0 DAH. Activity further increased until 10 DAH, especially after exogenous feeding. The highest trypsin activity was detected at 25 DAH as 119.26 ± 11.6 mU/mg protein⁻¹. It is concluded that exocrine pancreas organogenesis is the main critical step in the development of digestive system that results in zymogen granules accumulation and increased trypsin activity.     

Optimum ration level for better growth,conversion efficiencies and body composition of fingerling <Emphasis Type="Italic">Heteropneustes fossilis</Emphasis> (Bloch)

The effects of ration levels on growth, conversion efficiencies and body composition of fingerling Heteropneustes fossilis (6.8 ± 0.04 cm, 5.0 ± 0.02 g) were studied by feeding isonitrogenous (40% crude protein) and isocaloric (19.06 MJ kg⁻¹ gross energy) diets representing 1, 3, 5, 7 and 9% of the body weight (BW) day⁻¹ to triplicate groups of fish . Growth performance of the fish fed at the various ration levels was evaluated on the basis of live weight gain percentage (LWG%), feed conversion ratio (FCR), specific growth rate percentage (SGR%), protein retention efficiency (PRE%) and energy retention efficiency (ERE%) data. Maximum LWG% and SGR were obtained at a feeding rate of 7% BW day⁻¹, whereas best FCR (1.6), PRE% and ERE% were recorded at a feeding rate of 5% BW day⁻¹. Maximum body protein was also obtained for the group receiving the diet representing 5% of their body weight. However, a linear increase in fat content was noted with the increase in ration levels up to 7% BW day⁻¹. The SGR, FCR, PRE and ERE data were also analyzed using second-degree polynomial regression analysis to obtain more precise information on ration level, with the results showing that the optimal ration for these parameters was 6.8, 6.1, 5.9 and 6.2% BW day⁻¹, respectively. Based on the above second-degree polynomial regression analysis, the optimum ration level for better growth, conversion efficiencies and body composition of fingerling H. fossilis was found to be in the range of 5.9–6.8% of the BW day⁻¹, corresponding to 2.36–2.72 g protein and 88.20–101.66 MJ digestible energy kg⁻¹ diet day⁻¹.     

Histological development of digestive tract in discus, <Emphasis Type="Italic">Symphysodon</Emphasis> spp. larvae

The present study provides information on the histomorphological development of digestive system of discus, Symphyosodon spp., larvae during the first month of life. Discus larvae are altricial at hatching, with an undifferentiated digestive tract and a large yolksac, which is completely consumed within 7 days. The mouth opens 3 days after hatching (DAH) and the larvae starts feeding on AF Artemia at 4 DAH when offered. At 3 DAH the digestive tract is differentiated with distinct esophagus, stomach anlage, and mid- and hindguts. At 5 DAH, discus larvae is an active feeder, equipped with partly developed jaws and ossified gill arches and an inflated swim bladder. The liver and pancreas are present and supranuclear inclusion vacuoles (SIV) appear in the hindgut for the first time. Gastric glands in stomach were first observed 7 DAH and proliferated by 11–13 DAH. SIV were a common feature in the midgut and hindgut epithelium until 15–23 DAH. Therefore, exclusive use of artificial diets should be postponed until 2–3 weeks after hatching.     

Potential predation rates by the sea stars Asterias rubens and Marthasterias glacialis, on juvenile scallops, Pecten maximus, ready for sea ranching

The potential for predation by the sea stars Asterias rubens and Marthasterias glacialis on seed-size (41 ± 3 mm shell height) juvenile scallops (Pecten maximus), ready for seeding in sea ranching areas, was investigated in a 30-day laboratory predation experiment. There was no significant difference (P > 0.05) in predation rate of large A. rubens (95–115 mm radium) and large M. glacialis (120–164 mm radius), which averaged 0.88 and 0.71 scallops individual⁻¹ day⁻¹, respectively. Maximum rates of predation were 2.44 scallops individual⁻¹ day⁻¹ for large A. rubens and 3.00 scallops individual⁻¹ day⁻¹ for large M. glacialis. Small M. glacialis (76–87 mm radius) had a significantly lower predation rate than large individuals of either species (average 0.13 scallops individual⁻¹ day⁻¹, P < 0.05). Small A. rubens (50–80 mm radius) only began to prey on scallops when average scallop size was reduced to 35 mm. Based on estimated density of sea stars at a Norwegian sea ranching site and average predation rates, a population of scallops seeded at 10 m⁻² would be reduced by between 0.5 and 11% in 1 month. Furthermore, using the highest observed predation rate, the degree of loss of scallops indicated that scallop culture via sea ranching would not be economically viable and thus methods for reducing scallop predation by sea stars are necessary.     

Effects of the timing of initial feeding on growth and survival of loach (<Emphasis Type="Italic">Misgurnus anguillicaudatus</Emphasis>) larvae

The effects of delayed first feeding on growth and survival and starvation on the point-of-no-return of loach Misgurnus anguillicaudatus larvae were studied by evaluating morphometric characteristics under controlled conditions. Larvae began to feed exogenously at 3 days after hatching (DAH) and the PNR occurred between 9 and 10 DAH at 23 ± 1.0°C. The experimental design included a conventional feeding regime with initial feeding from 3 DAH as a control, delayed first feeding for 4, 5 and 6 DAH. Morphometric characteristics (head depth, body depth, eye diameter, mouth diameter, musculature height, total length and yolk sac volume) were evaluated under different initial feeding time (3, 4, 5 and 6 days after hatching). Loach larvae initiated first feeding at 4, 5 and 6 days after hatching achieved comparatively lesser growth performance in all morphometric characteristics than that of 3 days at the end of the experiment. By day 6, significant differences were observed between 3 and 6 days initial feeding larvae for all morphometric characteristics except eye diameter and mouth diameter. Similarly, significant differences were noticed between 3 and 5 days initial feeding. However, there were no significant differences in head depth, body depth, eye diameter, mouth diameter, and total length between 3 and 4 days initial feeding until 12 DAH. After 15 days rearing, significant differences in all morphometric characteristics appeared between 3 and 4 days initial feeding and followed to the end of the experiment. It was also observed that the yolk absorption in loach larvae was completed by 6 days irrespective of the differences in the initial feeding. The yolk volume of 4 and 5 DAH larvae initiated first feeding at 3 days (0.0125 ± 0.0015; 0.0077 ± 0.0009 mm³) had significant differences compared with yolk volume of larvae initiated first feeding at 4 days (0.0081 ± 0.0011; 0.0039 ± 0.0004 mm³), 5 days (0.0079 ± 0.0010; 0.0017 ± 0.0002 mm³) and 6 days (0.0082 ± 0.0011; 0.0016 ± 0.0001 mm³). Survival rates of four treatments were estimated daily for 30 days and significant differences were observed between the treatments at the end of the experiment. The final survival rate was higher when the loach larvae initiated feeding at 3 days (75.9%) when compared with 4 days (31.8%), 5 days (14.5%) and 6 days (6.4%). The present study suggests that the first feeding of loach larvae should be initiated at 3 DAH for achieving better growth and survival or else bad growth performance will engender if the first feeding is delayed.     

Determination of the optimum transfer time of kutum (<Emphasis Type="Italic">Rutilus frisii kutum</Emphasis>) larvae from live food to artificial dry feed

Kutum Rutilus frisii kutum is known as a valuable commercial species in the southern part of Caspian Sea. Artificial rearing of fry has been introduced as an alternative to supply kutum fry in order to restock the kutum population in the Caspian Sea. The aim of this study was to find the suitable time to transfer kutum larvae from live food to artificial feed. The experiment began on day 3 post- hatching and lasted for 21 days. Mean initial weight of larvae was 4.5 mg. Five experimental groups including Group A (zooplankton alone for 21 days), Group B (12 days zooplankton + 9 days artificial feed), Group C (8 days zooplankton + 13 days artificial feed), Group D (4 days zooplankton + 17 days artificial feed) and Group E (artificial feed alone for 21 days) were considered for this experiment. According to the obtained results, the specific growth rate of kutum larvae varied from 8.01 to 13.58% day⁻¹, and the highest and lowest specific growth rate were found in A and E treatments, respectively. The lowest mean body weight (24.6 mg) was found in larvae fed on artificial feed for 21 days. However, survival rates of kutum larvae fed mixed zooplankton for 8 and 12 days (85.83 and 89.33%, respectively) were comparable with those of larvae fed live food during the entire experiment (91.6%). The lowest survival rate (69.16%) was found in larvae fed artificial feed during the entire experiment.     

Growth and lipid composition of Atlantic cod (Gadus morhua) larvae in response to differently enriched Artemia franciscana

Considerable progress has been achieved in the intensive culture of Atlantic cod (Gadus morhua). However, there is little information concerning optimum live-feed enrichments for cod larvae, since many of the techniques used during the larviculture have been borrowed from other fish species and adapted for the production of Atlantic cod. The present study compared four different protocols for the enrichment of Artemia to be used as live feed for cod larvae. The protocols tested were: (1) AlgaMac 2000, (2) AquaGrow Advantage, (3) Pavlova sp. + AlgaMac 2000, and (4) DC DHA Selco + AlgaMac 2000. Larvae were fed differently enriched Artemia between 37 and 59 days post hatch. At the end of the experiment, larvae from treatment 1 [specific growth rate (SGR) = 10.4 ± 0.4% day⁻¹] grew faster than larvae from treatments 3 (SGR = 6.9 ± 0.2% day⁻¹) and 4 (SGR = 4.9 ± 0.4% day⁻¹, P < 0.0001). However, treatments 3 and 4 resulted in better larval survival at the end of the experimental period, estimated to be 3 on a scale from 1 to 5, whereas the survival estimates for the two other groups were 2. The treatments affected the fatty-acid composition of Artemia and of cod larvae. Larvae from treatment 1 had a higher percentage of AA (20:4ω6, P < 0.0001) and ω6DPA (22:5ω6, P < 0.0001) than the other larvae. Levels of DHA (22:6ω3) were similar in larvae from treatments 1 and 4, and higher than in the other larvae (P < 0.0001). Our results suggest that Artemia containing a DHA/EPA/AA ratio of 7/2/1 result in good larval performance. Joseph A. Brown—Deceased September 2005.     

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.     

Growth of giant tiger prawn, <Emphasis Type="Italic">Penaeus monodon</Emphasis> Fabricius,under co-culture with a discarded filamentous seaweed, <Emphasis Type="Italic">Chaetomorpha ligustica</Emphasis> (Kützing) Kützing,at an aquarium-scale

Growth of juvenile giant tiger prawn, Penaeus monodon Fabricius, was evaluated at an aquarium-scale in co-culture with a discarded filamentous seaweed, Chaetomorpha ligustica (Kützing) Kützing. Juveniles at different ages in days were examined, designated as J 16, J 44, J 58, J 93 and J 128, where a 1-day-old juvenile (J 1) is equivalent to a 20-day-old post-larva (PL 20)). Juveniles at every age group grazed directly on live C. ligustica, even those fed an artificial shrimp diet to satiation. Mean specific growth rate (SGR: % day⁻¹) was higher in early age juveniles. Compared to mono-culture, significant differences in growth were observed at J 16 (4.44% day⁻¹) and J 44 (1.60% day⁻¹); however, no significant differences were recorded at J 58 (1.16% day⁻¹), J 93 (0.75% day⁻¹) or J 128 (0.45% day⁻¹). It was concluded that co-culture of giant tiger prawn with C. ligustica has a dietary advantage, especially in early age juveniles.     

Screening of enzyme activity for assessing the condition of larvae in the seven-band grouper <Emphasis Type="Italic">Epinephelus septemfasciatus</Emphasis> and devil stinger <Emphasis Type="Italic">Inimicus japonicus</Emphasis>

We conducted screening tests to determine whether enzyme activity is a suitable biomarker for assessing the physiological condition of marine fish larvae. The rearing experiments consisted of three trials, of which two were conducted using the seven-band grouper Epinephelus septemfasciatus for a period of 5 days after hatching (DAH), and one was conducted using the devil stinger Inimicus japonicus for 10 DAH. The trials were conducted under three different rearing-tank environments (shallow tank, intermediate tank, deep tank) in a water volume of 100 l and an aeration rate of 50 ml/min. We determined survival, surface death, growth, and enzyme activities (trypsin, esterase, and alkaline phosphatase). The highest survival rates and lowest surface deaths in both species occurred among the larvae grown in the deep tank. There was a significant and negative correlation between survival at 5 DAH and alkaline phosphatase activity at 0 DAH in the seven-band grouper. The same correlation was found between survival at 10 DAH and trypsin and alkaline phosphatase activity at 1 DAH in the devil stinger. Based on these results, we conclude that the activity of a specific enzyme is a candidate for assessing the physiological condition of marine fish larvae.     

Effects of culture density and bottom area on growth and survival of the cuttlefish <Emphasis Type="Italic">Sepia</Emphasis><Emphasis Type="Italic">officinalis</Emphasis> (Linnaeus, 1758)

The effects of culture density and bottom areas on cuttlefish (Sepia officinalis) culture were studied. Cuttle fish were cultured under three experimental combinations of culture density and bottom area: (1) high density and small bottom surface area; (2) low density and large bottom area; (3) high density and large bottom area. Each experimental protocol was repeated in triplicate. Average weights at the end of the experiment were of 65.8 ± 5.8, 87.1 ± 5.6 and 78.7 ± 5.9 g for cuttlefish cultured under the conditions of protocol 1, 2, and 3, respectively; these differences were significant between each of the three groups. Total biomass increased faster (up to 7.5 kg per tank) under the high density/large bottom area conditions (protocol 3) due to the larger number of animals and low mortality in those tanks. Growth rates (%bw day⁻¹) were different between protocols, with growth rates of 2.1 ± 0.1, 3.0 ± 0.2, and 2.5 ± 0.1%bw day⁻¹ obtained for cuttlefish cultured according to protocol 1, 2, or 3, respectively. Average feeding rates were similar for the three groups—10.7 ± 0.8, 9.7 ± 2.0, and 9.6 ± 1.1%bw day⁻¹ for cuttlefish cultured according to protocols 1, 2, and 3, respectively, while food conversions (%) were different—21.5 ± 3.2, 32.4 ± 2.5, and 27.0 ± 1.1%bw day⁻¹, respectively. Total mortality was high in the high density/small bottom area tanks, 30%, while it was very low for the groups cultured under conditions of low and high density/large bottom area, 4%. Based on these results, we conclude that culture conditions that provide large bottom areas also provide good survival conditions and promote growth in comparison those with small bottom areas, even under conditions of lower culture densities.     

Growth and survival of grouper <Emphasis Type="Italic">Epinephelus</Emphasis><Emphasis Type="Italic">coioides</Emphasis> (Hamilton) larvae fed free-living nematode <Emphasis Type="Italic">Panagrellus redivivus</Emphasis> at first feeding

The free-living nematode, Panagrellus redivivus, was tested as live food for grouper Epinephelus coioides larvae during the first feeding stage. A series of experiments were conducted to determine the acceptability of the free-living nematodes in grouper larvae at first feeding, the optimum nematode density and the response of the larvae to nutritionally enriched nematode. All experiments were conducted in 200-L conical tanks filled with 150-L filtered seawater and stocked at 15 larvae L⁻¹. Duration of feeding experiments was up to day 21 (experiment 1) and 14 days (experiment 2 and 3). Brachionus plicatilis and Artemia (experiment 1) and Brachionus plicatilis alone (experiment 2 & 3) was used as the control treatment. Observations indicated that the grouper larvae readily fed on free-living nematodes as early as 3 days posthatching, the start of exogenous feeding. Optimum feeding density for the larvae was 75 nematodes ml⁻¹. The enrichment of cod liver oil or sunflower oil influenced the total lipids and n-3 highly unsaturated fatty acids of P. redivivus, which in turn influenced those of the grouper larvae, however, growth and survival of the larvae were not affected (P > 0.05). The results from this investigation showed that the nematode, P. redivivus, can be used as first live food for grouper larvae from the onset of exogenous feeding until they could feed on Artemia nauplii.     

Use of acceleration loggers in aquaculture to determine net-cage use and field metabolic rates in red sea bream <Emphasis Type="Italic">Pagrus major</Emphasis>

We investigated the usefulness of acceleration loggers in aquaculture by examining net-cage use and metabolic rates in red sea bream, Pagrus major. First, the fish’s metabolic rate (mg O₂ kg⁻¹ min⁻¹) was measured with the logger in a swim tunnel at designated water velocities. We found that metabolic rate could be expressed by using a linear regression model of the activity rate index (unitless min⁻¹) derived from acceleration data. Using this equation, the field metabolic rates of three fish in a net cage were monitored and were estimated at 14.1–15.0 kcal kg⁻¹ day⁻¹. The results suggested that 15–19% of energy from satiation feeding ration was consumed for metabolism and activity in the net cage. The loggers showed orderly net-cage use by the fish. Tagged individuals used the whole cage from surface to bottom, but individual fish that preferred the surface area rarely used the bottom, and vice versa. Metabolic rate increased significantly with distance of the fish from their preferred depths. The logger provided information on the physiological and behavioral responses of fish in a given breeding system, and its use should contribute to the design of practical aquaculture systems.