The role of fatty acids enrichments in the larviculture of false percula clownfish Amphiprion ocellaris

At present, clownfishes are the best example of successfully captive bred ornamental specimens but little is known about the relationship between food enrichment and both larval growth and development. In fact, it is well known that a certain percentage of these fishes cultured in captive conditions show a miss-band pigmentation. In the present study, the effects of live prey enrichment on growth and pigmentation in false percula clownfish (Amphiprion ocellaris) larvae were tested.Newly hatched A. ocellaris larvae were divided in three different groups and fed as follows: group A fed on enriched (Algamac 2000) B. plicatilis (10 ind./mL) from day 1 to day 5 post-hatch (ph); group B fed on enriched (Algamac 2000) B. plicatilis (10 ind./mL) followed by Artemia nauplii (5 ind./mL;) and group C fed on Algamac 2000 enriched B. plicatilis and Algamac 2000 enriched Artemia nauplii.Samples of the larvae were collected on day 5 from group A and on day 11 ph in group B and C for morphometric and molecular analysis. On day 11 ph food enrichment resulted in a better growth of group C larvae respect to those of group B fed on not enriched Artemia nauplii (15.8 ± 0.2 mg and 8.78 ± 0.02 mm vs. 6.8 ± 0.2 mg and 6.93 ± 0.01 mm). Moreover, 36 ± 2% of the juveniles obtained from group B showed a miss-band pigmentation as compared to 29 ± 1% of the juveniles obtained from group C. At molecular level, the results obtained by Real-Time PCR are in agreement with the morphometric ones: a positive induction of the Insulin-like Growth Factor II (IGFII) and Peroxisome Proliferator Activated Receptor α and β (PPARα and PPARβ) gene expression and a reduction of Myostatin (MSTN) was observed in group C larvae fed on enriched live prey. IGFI gene expression was higher in group B.The present study provides clear evidences of the positive role of Algamac 2000 on growth and pigmentation of captive cultured false percula clownfish.     

Ammonia toxicity and its effect on the growth of the South African abalone Haliotis midae Linnaeus

The current study investigated acute toxicity to ammonia of the South African abalone, Haliotis midae, from three size classes relevant to mariculture operations, and the chronic impact of sub-lethal ammonia levels on growth of juvenile abalone.Results showed that tolerance to ammonia (at pH 7.8 and T_a = 15 °C) increases with body size (i.e. age) as indicated by 36 h LC₅₀ values: juvenile abalone (1-2.5 cm shell length) had the lowest LC₅₀ of 9.8 μg l^− 1 FAN, whereas LC₅₀ was 12.9 μg l^− 1 FAN in “cocktail”-size abalone (5-8 cm shell length). The highest LC₅₀ of 16.4 μg l^− 1 FAN was observed in “brood stock”-size animals (10-15 cm). When “cocktail”-size abalone were allowed to acclimatize to sub-lethal ammonia levels for 48 h, their ammonia tolerance increased compared with non-acclimatized abalone of the same size: LC₅₀ was 2.0 μg l^− 1 FAN higher at 14.8 μg l^− 1 FAN.Growth of juvenile abalone (1-2.5 cm shell length) during chronic exposure to sub-lethal FAN levels is inhibited: specific growth rate (SGR) is significantly reduced by 58.7% to 0.10 ± 0.03% d^− 1 (weight) compared with 0.24 ± 0.06% d^− 1 of abalone of a control group (no ammonia).The results demonstrate the negative effects of ammonia not only on survival but also on growth of farmed abalone, both impair profitability of the farming operation. The information from the present study will be helpful in determining water quality requirements in South African abalone farms.     

Rearing of African catfish (Clarias gariepinus) and vundu catfish (Heterobranchus longifilis) in traditional fish ponds (whedos): Effect of stocking density on growth, production and body composition

African catfish (Clarias gariepinus) (initial body weight: 34.8 ± 4.8 g) and vundu catfish (Heterobranchus longifilis) (initial body weight: 39.1 ± 8.2 g) fingerlings were stocked at densities of 4, 6 or 8 fish m^− 3 in traditional fish ponds (whedos) constructed in the floodplain of the Oueme River (South Benin, West Africa), for 70 days from March to June 2005. Fish were fed twice a day with 34% crude protein feed formulated with locally available ingredients. The effects of stocking density were evaluated in growth responses, gross production and body composition. Water quality variables were similar (p > 0.05) in all compartments. Temperature and pH were at the optimum level for fish. Dissolved oxygen ranged from 0.9 to 1.2 mg l^− 1 during the experiment and secchi disc transparency was low (< 14 cm). In both species, growth responses increased with the increasing density, significantly in African catfish stocked at density of 8 fish m^− 3 compared to the other densities (4 and 6 fish m^− 3) but not significantly in vundu catfish. Production data ranged from 3.1 ± 0.5 to 22.8 ± 4.5 t ha^− 1 year^− 1 in African catfish and from 6.1 ± 1.2 to 15.1 ± 3.1 t ha^− 1 year^− 1 in vundu catfish. Production increased with increasing stocking densities but only significantly (p < 0.05) between the density of 8 fish m^− 3 and the other densities. In both species, carcass fat increased with increasing density (p < 0.05) while carcass protein and moisture decreased (p > 0.05). These results are important because they indicate that, as far as growth rate and production are concerned, African catfish is more profitable than vundu catfish for culture at high density in whedo.     

Effect of saponin on hematological and immunological parameters of the giant freshwater prawn, Macrobrachium rosenbergii

Giant freshwater prawns, Macrobrachium rosenbergii (17.9 ± 2.7 g), exposed to different concentrations of saponin at 0, 0.3, 0.6, 0.9 and 1.2 mg l^− 1 for 168 h were examined for osmolality, electrolyte levels, oxyhemocyanin, protein levels, acid-base balance status, total hemocyte count (THC), phenoloxidase activity, and respiratory bursts. Hemolymph oxyhemocyanin, protein, and pO₂ were inversely related to the saponin concentration. Hemolymph oxyhemocyanin, protein, pO₂, pCO₂, and pH of prawns exposed to 1.2 mg l^− 1 saponin were significantly lower than those of prawns exposed to 0.3 mg l^− 1 and control solutions. However, no significant difference was observed in osmolality or electrolyte levels of prawns exposed to different concentrations of saponin for 168 h. The THC of prawns following 168 h of exposure to 0.9 and 1.2 mg l^− 1 saponin increased, but the phenoloxidase activity decreased suggesting that the decrease in phenoloxidase activity under saponin stress was not a consequence of the increase in THC. We concluded that saponin at as low as 0.9 mg l^− 1 decreases the respiratory protein level and acid-base balance, and modulates the immune system of M. rosenbergii.     

First feeding of Octopus vulgaris Cuvier, 1797 paralarvae using Artemia: Effect of prey size, prey density and feeding frequency

Different assays related to the first feeding of Octopus vulgaris Cuvier, 1797 are compiled in this paper. They include: age at initial feeding age, prey size selection and optimal density, attack timing after feeding, and effect of dose number on the number of captures. Prey capture and ingestion processes were also analysed. Food supplied was cultured Artemia sp. Each assay lasted 15 min.Although paralarvae already start to feed on the hatching day (day 0), it is during day 2 when a greater number of attacks is recorded (81.7 ± 14.7% paralarvae attack). They mainly prefer (significance level α = 0.05) large Artemia, 1.4 ± 0.4 mm (77.0 ± 5.6% of the total attacks) than small Artemia, 0.8 ± 0.1 mm (23.0 ± 5.6%). There is also a slight predilection for the lowest Artemia concentration (33.3 ±12.6% paralarvae attack in a 0.1 Artemia ml^− 1 density, opposite 16.7 ± 7.6 and 18.3 ± 7.6% in densities of 0.5 and 1 Artemia ml^− 1 respectively). The greatest predatory activity is recorded during the first 5 min after food is supplied (72.2 ± 25.5%). An increase in the predatory activity was also observed when food was distributed in several doses instead of a single dose (75.0 ± 10.0% and 46.7 ± 17.6% respectively). It was proved for the first time that paralarvae completely ingest their preys (including their exoskeletons), in this case Artemia. Time needed for their total ingestion ranges between 4 and 10 min.     

Gill ATPase activities of silver perch, Bidyanus bidyanus (Mitchell), and golden perch, Macquaria ambigua (Richardson): Effects of environmental salt and ammonia

The Australian freshwater fish, silver and golden perch, are increasingly being used for aquaculture. Addition of salt to water is commonly used in commercial aquaculture to reduce stress attributed to high ammonia concentrations. The activities in gill homogenates of ouabain-sensitive Na⁺/K⁺-ATPase and NEM-sensitive ATPases (as a measure of H⁺-ATPases) of silver and golden perch were measured after maintaining the fish in water containing different salt and ammonia concentrations. Six treatments were applied in a 2 × 3 factorial design: two salt treatments, low salt (LS) of 2.5 g l^− 1 and high salt (HS) 5 g l^− 1, and three ammonia treatments, no added ammonia (NA), low ammonia (LA), 3 mg total ammonia nitrogen (TAN) l^− 1 and high ammonia (HA), 5 mg TAN l^− 1. In both species, activity of Na⁺/K⁺-ATPase was lowest in fish kept in the LSNA treatment (7.4 ± 0.4 μmol Pi mg protein^− 1 h^− 1 for silver perch and 3.1 ± 0.6 for golden perch) and highest in the HSHA treatment (15.2 ± 1.0 μmol Pi mg^− 1 protein h^− 1 for silver and 8.4 ± 1.2 for golden perch). In both species there was a significant increase (P < 0.001) in Na⁺/K⁺-ATPase activity with increase in salt concentration and with an increase in ammonia concentrations. A significant interaction (P < 0.036) between salt and ammonia on Na⁺/K⁺-ATPase activity was observed in silver but not in golden perch. In contrast, the lowest activity for NEM-sensitive ATPase was observed in the HSNA treatment (1.0 ± 0.2 μmol Pi mg^− 1 protein h^− 1 for silver and 1.5 ± 0.4 for golden perch) and highest in LSHA treatment (2.9 ± 0.4 μmol Pi mg^− 1 protein h^− 1 for silver and 3.6 ± 1.2 for golden perch). In both species there was a significant decrease in NEM-sensitive ATPase activity with increase in salt concentration and an increase in activity with increase in ammonia (P < 0.003). In silver perch, a significant interaction between the treatments was observed (P < 0.02). The results suggest that in these species of freshwater fish the Na⁺/K⁺-ATPase has a role in salt and ammonia homeostasis and that the NEM-sensitive ATPases are more active in fish kept in water with a lower salt content. It is possible that the increase in ammonia resistance when salt is added to the environmental water in commercial aquaculture systems may be due to the effects of salt on gill Na⁺/K⁺-ATPase activity rather than the NEM-sensitive ATPases.     

Intensive production of juvenile tiger shrimp Penaeus monodon: An evaluation of stocking density and artificial substrates

Tiger shrimp Penaeus monodon were intensively grown from PL₁₅ for 56 d in tank systems at stocking densities of 1000 and 2000 shrimp m^− 3, with and without the addition of artificial substrates (AquaMat® (buoyant and non-buoyant) and polyethylene mesh) at each density. Shrimp growth was significantly greater at the lower density and when substrates were added. Mean shrimp weight at harvest ranged from 0.64 ± 0.06 g (2000 shrimp m^− 3, no added substrate) to 1.17 ± 0.01 g (1000 shrimp m^− 3, added substrate). Survival was high and averaged 79.5 ± 2.7% across all treatments. The addition of substrates significantly increased survival at both stocking densities; however, survival was not significantly affected by stocking density. A maximum harvest density of 1645 shrimp m^− 3 and biomass of 1.27 kg m^− 3 were produced at a stocking density of 2000 m^− 3 with added substrates. Both harvest density and biomass significantly increased with stocking density and addition of substrates. The feed conversion ratio (FCR) of formulated feed was significantly lower when substrates were added. The results show that growth of P. monodon juveniles was inversely related to stocking density during intensive production. However, production output was significantly increased by addition of artificial substrates, which enhanced both growth and survival.     

Effects of dietary vitamin C on survival, growth, and immunity of large yellow croaker, Pseudosciaena crocea

An 8 weeks growth experiment was conducted to determine the effects of dietary vitamin C on the survival, growth, tissue ascorbic acid contents and immunity of large yellow croaker (Pseudosciaena crocea) with initial weight of 17.82 ± 0.68 g. Seven practical diets were formulated to contain 0.1, 12.2, 23.8, 47.6, 89.7, 188.5 and 489.0 mg ascorbic acid equivalent kg^− 1 diet, supplied as l-ascorbyl-2-polyphosphate (LAPP). Each diet was fed to triplicate groups of fish in seawater floating cages (1.5 × 1.5 × 2.0 m), and each cage was stocked with 120 fish. Fish were fed twice daily (05:00 and 17:00) to apparent satiation for 8 weeks. The water temperature fluctuated from 19.5 to 25.5 °C, the salinity from 25 to 28‰ and dissolved oxygen content was approximately 7 mg l^− 1 during the experimental period. Results showed that the specific growth rate (SGR) (from 1.80 to 1.96% d^− 1) had an increasing trend with the increase of dietary vitamin C, but no significant difference was observed among dietary treatments. No gross deficiency signs were observed in any of the experimental fish. Survival rate, however, significantly increased with increasing dietary vitamin C (P < 0.05). The vitamin C contents in liver and muscle correlated positively with the vitamin C in diets. The vitamin C requirement was estimated to be 28.2 mg kg^− 1 based on survival, and 87.0 mg kg^− 1 on liver content of vitamin C. The activities of serum lysozyme and alternative complement pathway (ACP), phagocytosis percentage (PP) and respiratory burst activity of head kidney significantly increased with increasing dietary vitamin C. The challenge experiment with Vibrio harveyi showed that fish fed the diets with supplementation of vitamin C had significantly lower cumulative mortality compared to the control group (66.7%), and the cumulative mortality (16.7%) in fish with 489.0 mg kg^− 1 ascorbic acid was significantly lower than that (41.7%) in fish with 23.8 mg kg^− 1 ascorbic acid. These results suggested that vitamin C significantly influenced the immune response and disease resistance of large yellow croaker.     

Inducing relaxation in the queen conch Strombus gigas (L.) for cultured pearl production

Five potential relaxant chemicals were evaluated: 2-phenoxyethanol, menthol crystals, benzocaine, MS-222, and magnesium chloride to induce relaxation in the queen conch for cultured pearl production. S. gigas were exposed to each chemical and were observed continuously for 30 min. Conch were placed on the bottom of the container with the aperture facing upwards (i.e., in an inverted position). When conch returned to their ‘normal’ position, they were turned facing upwards again. This process continued until conch were unable to return to their normal position. Only 30 g L^− 1 magnesium chloride induced adequate relaxation in S. gigas to attempt pearl seeding. Conch exposed to all other treatments, except 0.25 g L^− 1 menthol, showed a strong ‘kicking’ (escape) reaction during the initial 2 min to 7 min of exposure. After such reaction, conch retracted into their shells and within the 30 min exposure period they showed no signs of relaxation. Conch exposed to 0.25 g L^− 1 menthol did not attempt to right but slowly retracted into their shells and did not show signs of relaxation. Conch can be relaxed in 20 min with magnesium chloride. They showed an extended mantle, a relaxed foot and a slow response to physical manipulation.     

The effects of fish hydrolysate (CPSP) level on Octopus maya (Voss and Solis) diet: Digestive enzyme activity, blood metabolites, and energy balance

As has been demonstrated in previous studies, Octopus maya can be fed on artificial diets. In the present study six different diets were assayed. Five diets were designed to test the effect of percentage of inclusion of fish protein concentrate (CPSP: 0, 5, 10, 15, and 20%) and were offered to octopuses as a specifically designed artificial diet. The sixth diet consisted of frozen crab (Callinectes spp) and was used as control diet. Blood metabolites and energy budget of octopuses were evaluated to determine how CPSP levels modulate the digestive capacity and allow retaining energy for growth. Wild animals (316.4 ± 9.8 g) were used in the study. Results showed that CPSP produced a positive specific growth rate (SGR, % day^− 1) with high value in octopuses fed 15% CPSP level. A maximum growth rate of 0.86% day^− 1 was recorded in these animals, a value that is extremely low when compared with the SGR obtained when animals were fed fresh crab (3.7% day^− 1). In general, blood metabolites were affected by diet composition, indicating that some metabolites could reflect the nutritional and/or physiological status of octopus. Preliminary reference values for O. maya fed crab were found for glucose (0.09 ±0.02 mg/ml), lactate (0.004 ± 0.002 mg/ml), cholesterol (0.16 ± 0.02 mg/ml), acylglycerol (0.14 ± 0.01 mg/ml), protein (0.37 ± 0.04 mg/ml), hemocyanin (1.85 ± 0.04 mmol/l), and digestive gland glycogen (1.86 ± 0.3 mg/g). Total energy content can be used as an indicator of tissue metabolic reserves. In the present study, higher energy content in the digestive gland and muscle was observed in octopuses fed crab, followed by animals fed 15% CPSP. Results from the digestive gland indicated that the retained energy derived from glycogen, suggesting that lipids and protein were the main sources of variation linked with energy content. In general, digestive gland proteases activity and trypsin were induced in octopuses fed 15% CPSP. The capacity of O. maya juveniles to adjust their digestive enzymes to different types of food was evidenced. Essential amino acid content (EAA) of the diet was not a limiting factor. When dietary EAA profiles were compared with O. maya EAA profiles, all dietary EAA resulted in a higher concentration than whole body octopus composition. In the present study, all experimental groups ingested between 3300 and 4106 kJ wk^− 1 kg^− 1 without statistical differences among treatments, indicating that experimental diets were as attractive as crab. Differences were recorded in the proportion of absorbed energy (Ab, %) between CPSP-based and crab meat diets, suggesting digestion limitations associated with artificial diets. The present results indicate that the 15% CPSP diet had characteristics that stimulate digestive enzymes and reduce energetic costs associated with its digestion (HiE or SDA), channeling more biomass production than the other experimental diets.     

The effect of trigger depth on self-feeder utilisation, growth and the vertical distribution of tank-held rainbow trout Oncorhynchus mykiss (Walbaum)

This study investigated the effect of placing a self-feeding trigger at either a) 1 cm below the water surface or b) mid-water (35 cm below the surface), on self-feeder usage, growth, feed wastage and fin damage of juvenile rainbow trout, Oncorhynchus mykiss (Walbaum). The vertical distribution of trout was also measured for the first 31 days of self-feeding. Group-held trout (n = 10 fish group^− 1, 5 groups treatment^− 1), weighing 51.06 g ± 8.09 g (mean ± SD) were held in 200 l cylindroconical tanks (depth = 75 cm) for 62 days. Trigger placement had no significant effect upon self-feeder conditioning, and upper trigger group (UTG) and lower trigger group (LTG) fish took an average of 16 ± 7.4 days and 14 ± 9.8 days to reach a stable level of self-feeding, respectively. Specific growth rate was significantly higher in UTG fish (1.83 ± 0.20 vs. 0.95 ± 0.21 for UTG vs. LTG fish, respectively) whilst condition factor and self-feeder utilisation (ration size, 1.21 ± 0.18 vs. 0.52 ± 0.15 kg tank^− 1 for UTG vs. LTG fish) were also significantly higher in UTG fish. Trigger depth had no significant effect on size heterogeneity, mortality, feed wastage, feed conversion ratio (FCR) or the incidence of caudal and dorsal fin splitting and fin erosion. Dorsal fin splitting decreased with time in UTG but not in LTG fish. Caudal fin erosion increased with time in UTG (upper lobe only) and LTG (both lobes). The vertical distribution of fish also differed between treatments and more LTG fish preferred the lower part of the tank. Placing a self-feeding trigger at a mid-water depth can significantly limit growth, condition factor and self-feeder utilisation in juvenile rainbow trout, in addition to hindering recovery from dorsal fin erosion.     

Growth, survival and biochemical composition of spider crab Maja brachydactyla (Balss, 1922) (Decapoda: Majidae) larvae reared under different stocking densities, prey:larva ratios and diets

The spider crab Maja brachydactyla is overexploited on the NW coast of Spain. Aquaculture of this species can be the solution to the problem, and consequently, several attempts of intensive larval rearing have been conducted. However, most of the studies already published do not provide enough zoo technical data, especially in terms of larval and prey densities or the nutritional quality of diets used for rearing.Three experiments were carried out to evaluate the conditions for intensive larval rearing of M. brachydactyla. Larval stocking density (10, 50 and 100 larvae L^− 1), prey:larva ratio (15, 30 and 60 enriched Artemia larva^− 1) and diet (enriched Artemia, non-enriched Artemia and polychaete supplement) effects on growth and survival of this species were studied. For larval culture nine, 35 L, 150 μm mesh-bottomed PVC cylinders (triplicates for each treatment and larval stage) connected to a recirculation unit, were used. Temperature and salinity were kept constant at 18 °C and 36‰ respectively. A 12 to 18 day trial was conducted for each experiment and samples of larvae were collected at each larval stage (zoea I, zoea II, megalopa) in the inter-molt phase and at first juvenile. Survival, carapace length and width, dry weight (DW), and proximate biochemical content (protein, carbohydrates and total lipid) as well as lipid class composition were determined.Stocking densities of 100 larvae L^− 1 resulted in higher growth in DW and higher content in lipids and protein for zoea I (ZI) and zoea II (ZII) than 10 larvae L^− 1. However, survival decreased with increasing stocking density.The use of 60 preys larva^− 1 produced larvae with significantly higher DW and protein content, especially at ZII stage, than lower prey densities. Survival rate obtained feeding 60 preys larva^− 1 up to the megalopa stage was almost two-fold (42.2%) the rate obtained using 15 preys larva^− 1 (24.8%).Larvae fed on enriched Artemia (EA) showed an increase in weight up to megalopa (518.9 ± 26.5 μg) in contrast to larvae fed on non-enriched prey (A) (467.9 ± 6.9 μg). Variation in DW correlated with the total lipid content (L) of the larvae (L_EA = 70.1 ± 37.5 μg ind^− 1; L_A = 28.9 ± 3.2 μg ind^− 1) especially in terms of neutral lipids. The use of an initial density of at least 50 larvae L^− 1 and 60 enriched Artemia larva^− 1 can be considered the most adequate rearing parameters in order to obtain good results in growth and survival of M. brachydactyla.     

The influence of stocking density, light and temperature on the growth, production and nutrient removal capacity of Porphyra dioica (Bangiales, Rhodophyta)

The optimal conditions for growth of Porphyra dioica gametophytes were investigated in the laboratory, focusing on bioremediation potential. Porphyra dioica is one of the most common Porphyra species along the northern coast of Portugal and can be found year-round. The influence of stocking density and photon flux density (PFD) on the growth, production and nutrient removal was tested. Maximum growth rates, up to 33% per day, were recorded with 0.1 g fw l^− 1 at 150 and 250 μmol photons m^− 2 s^− 1. Growth rate decreased significantly with increasing stocking density. Productivity (g fw week^− 1) had an inverse trend, with more production at the higher stocking densities. At 150 μmol m^− 2 s^− 1 and with 1.5 g fw l^− 1, 1.4 g fw week^− 1 were produced. At this PFD, there was no significant difference in production between 0.6 to 1.5 g fw l^− 1. Nitrogen (N) content of the seaweeds decreased with increasing stocking densities and PFDs. The maximum N removal was recorded at 150 μmol m^− 2 s^− 1, with 1.5 g fw l^− 1 stocking density (1.67 mg N day^− 1). However, the N removed by thalli at 50 μmol photons m^− 2 s^− 1 was statistically equal to that at 150 and 250 μmol photons m^− 2 s^− 1, at a stocking density of 1.0 g fw l^− 1. The influence of temperature and photoperiod on growth and reproduction was also assessed. Growth rates of P. dioica were significantly affected by temperature and photoperiod. In this experiment (with 0.3 g fw l^− 1 stocking density), the highest growth rate, 27.5% fw day^− 1, was recorded at 15 °C and 16 : 8¯, L : D¯. Male thalli started to release spermatia 21 days after the beginning of the experiment, in temperatures from 10 to 20 °C and with 10, 12 and 16 h of day length. Unfertilized female-like thalli were observed at 10 to 20 °C, under all photoperiods tested. Growth of these thalli declined after 4 weeks. By then, formation of young bladelets in the basal portion of these thalli was observed. After 7 weeks all biomass produced was solely due to these vegetatively propagated young thalli, growing 22.4% to 26.1% day^− 1. The results of this study showed that P. dioica appears to be a candidate as a nutrient scrubber in integrated aquaculture systems.     

Disruption of gonadal maturation in cultured Senegalese sole Solea senegalensis Kaup by continuous light and/or constant temperature regimes

A major problem in the development of Senegalese sole Solea senegalensis intensive culture is the poor control on reproduction, in part due to the lack of knowledge on the precise role of photoperiod and temperature. Thus, gonadal maturation was evaluated by assessing the sequential changes in plasma levels of 17β-estradiol (E₂), 11-ketotestosterone (11-KT), and testosterone (T) in both female and male cultured Senegalese sole (F1 generation) exposed to various combinations of constant or naturally-fluctuating daylength and water temperature. Under natural photoperiod (NP; 36° N), exposure to constant temperature (t0; 18-20 °C) disrupted gonadal development, as indicated by a lower incidence (in comparison with naturally-fluctuating water temperature; 14-24 °C) of females at advanced maturation (from February to April: 12 vs. 33%) and running males (from February to May: 46% vs. 57%), and the reduced mean (± S.E.M.) sex steroid plasma levels (female peak E₂ levels: 2.9 ± 0.28 vs. 1.8 ± 0.3 ng ml^− 1; male peak T levels: 1.5 ± 0.14 vs. 0.9 ± 0.06 ng ml^− 1). Therefore, the onset and progression of gonadal development in this species seem to be strongly (“proximally”) influenced by fluctuating water temperature. When compared to NP and t0, exposure to continuous light (LL) under t0 significantly reduced steroid production (female peak E₂ levels: 1.8 ± 0.28 vs. 0.5 ± 0.05 ng ml^− 1; male peak 11-KT levels: 9.4 ± 1.06 vs. 5.4 ± 1.33 ng ml^− 1) and subsequently gonadal development (lower proportions of females at intermediate [46 vs. 6%] and advanced maturation [12 vs. 0%] from February to April and of RM [46 vs. 33%] from February to May). Thus, the seasonal changes of daylength would be crucial for normal gonadal development, being its cueing effects of higher magnitude than those of water temperature. The present report constitutes the first systematic study focused on the environmental control of reproductive events in Senegalese sole.     

Productivity and photosynthetic efficiency of outdoor cultures of Tetraselmis suecica in annular columns

In this study, 120-l annular columns were used to cultivate Tetraselmis suecica outdoors. The mass transfer at different aeration rates and the influence of the harvest rate on productivity and biochemical composition were investigated. The potential of the system was evaluated by estimating productivity at full-scale. Two different arrangements to simulate a full-scale plant and determine the “overall areal productivity” (OAP) were experimented with. In August 2003, one experimental column (full-scale column) was placed between seven dummy columns. All the reactors were positioned at a distance of 0.8 m wall to wall and centred at the vertices of equilateral triangles. A second experimental column (isolated column) was placed in a separate area under full sunlight. In August 2004, the columns were placed side by side in an east-west oriented row at a distance of 0.24 m wall to wall.In the first experiment, the mean volumetric productivity of the full-scale column was not significantly lower than that achieved by the isolated column (0.46 against 0.49 g l^− 1 day^− 1) in spite of the shading by the dummy units. The average OAP and efficiency of conversion of visible solar radiation (PE) were 36.3 g m^− 2 day^− 1 and 9.4%, respectively. In the second experiment, the full-scale column attained a mean volumetric productivity of 0.42 g l^− 1 day^− 1. The OAP and the PE were 38.2 g m^− 2 day^− 1 and 9.3%, respectively.     

Nile tilapia (Oreochromis niloticus) seed production in irrigated rice-fields in Northwest Bangladesh—an approach appropriate for poorer farmers?

Participatory research was conducted with poorer farmers in two communities, Girai (G) and Bahagili (B) in NW Bangladesh to assess the production of Nile tilapia seed in irrigated spring rice-fields. All the selected households (G = 15; B = 4) had previous experience producing common carp (Cyprinus carpio) in the rice-fields allocated a separate plot in which a deeper area had been excavated for this trial. Mature GIFT strain Nile tilapia (12 female and 6 male; 121 ± 34 g and 158 ± 54 g size, respectively) were supplied to each household irrespective of the size of their trial plot (mean < 0.15 ha). The trial started in the spring rice season (boro) in February and ended at the end of main season (amon) in December 1999. Management practices, production and sales of fish were monitored weekly.The majority of farmers succeeded in producing fingerlings in their plots; 11% failed totally but around 70% produced more than 2000 fingerlings from a single plot. Production during boro and fallow period was much higher (> 90% total) than during the subsequent amon crop (< 10% total). Total production was highly variable among households but not different between the two study areas (G = 4092 ± 3277; B = 3730 ± 4232 fingerlings household^− 1). Daily production of fingerlings per unit area was relatively low (< 1 fish m^− 2 day^− 1) but efficiency of production was high, averaging 17.3 fingerlings. kg^− 1 female day^− 1. Mean individual harvest weight was 21 g.Most fingerlings were sold (43%) and/or stocked for further culture in their own grow-out system (39%), but some were used directly for household consumption (17%).     

The tetrasporophyte of Asparagopsis armata as a novel seaweed biofilter

The red seaweed Asparagopsis armata (Harvey; Rhodophytae, Bonnemaisoniaceae) produces biologically active secondary metabolites that are valuable natural ingredients for cosmetics and medicine and its cultivation may therefore be a profitable venture. The tetrasporophyte of this species (“Falkenbergia rufolanosa”) was successfully tank-cultivated as a continuous biofilter for the effluent of a commercial fish farm in southern Portugal. Optimal stocking density for highest biomass yield and a low level of other algal species in winter and late spring was 5×g centrifuged fresh weight l^− 1. The effect of total ammonia nitrogen supply (TAN flux) on biofiltration and biomass yield was investigated in winter and spring. Results revealed that A. armata is currently the seaweed-biofilter with the highest TAN removal of up to 90 μmol l^− 1 h^− 1 at a TAN flux of about 500 μmol l^− 1 h^− 1. In the tanks used, this is equivalent to a removal of up to 14.5 g TAN m^− 2 day^− 1. At a lower TAN flux of about 40 μmol l^− 1 h^− 1, TAN removal by A. armata is more than double to what is reported at this flux for another successful seaweed biofilter, the genus Ulva. Monthly variation of A. armata biomass yield peaked in May and was lowest in January. At TAN fluxes between 300 and 400 μmol l^− 1 h^− 1, an average water temperature of 21.7 °C and a total daily photon flux density of 47 Mol m^− 2, seaweed yield was over 100 g DW m^− 2 day^− 1 with a recorded maximum of 119 g. During spring, autumn and early summer, the biomass of A. armata within the experimental tanks doubled every week. A model for the up scaling of this finfish integrated aquaculture of A. armata varies the investment in biofilter surface area and estimates the return in biofiltration and biomass yield. Highest TAN removal efficiencies will only be possible at low TAN fluxes and a very large biofilter area, resulting in a low production of biomass per unit area. To remove 50% of TAN from the effluent (1 mt Sparus aurata; 21 °C), 28 m² of biofilter, designed to support a water turnover rate of 0.8 Vol h^− 1 would be necessary. This system produces 6.1 kg FW (1.5 kg DW) of A. armata per day and has the potential to turn biofiltration into an economically sustained, beneficial side effect.     

Selective particle feeding by the Chilean oyster, Ostrea chilensis; implications for nursery culture and broodstock conditioning

Hatchery broodstock conditioning and nursery culture of the Chilean flat oyster Ostrea chilensis have been hampered by the poor performance of oysters fed typical microalgal hatchery diets. To determine the feeding capabilities of this species the selective removal and consumption of natural planktonic assemblages and artificial inert particles (polystyrene beads) by juvenile and adult oysters were examined experimentally. The arrangement of the eulaterofrontal cirri of the ctenidia was also examined to infer their potential efficiency of particle selection for feeding. Polystyrene beads of 45 and 15 μm in diameter had high rates of removal from suspensions by both juvenile (45 μm = 70%, 15 μm = 73%) and adult (45 μm = 88%, 15 μm = 87%) oysters. In contrast, beads of 6 μm diameter had lower rates of removal (adults = 68%, juveniles = 53%), while 1 μm beads were not removed at all. Both adult and juvenile oysters feeding upon natural plankton assemblages removed only microphytoplankton (20-75 μm in size) despite the presence of nanophytoplankton (2-20 μm), picophytoplankton (< 2 μm), cyanobacterium Synechoccocus spp. (< 2 μm), and bacterial cells (< 75 μm) in the experimental suspensions. Eulaterofrontal cirri of both juvenile (15.2 μm ± 0.9 SE) and adult oysters (18.9 μm ± 0.3 SE) are the shortest that have been reported for any ostreid species which helps to explain the inability of this species to retain small food particles. The clearance rates for oysters feeding on microphytoplankton only were 1.49 (± 0.05 SE) and 7.1 (± 1.2 SE) l h^− 1g^− 1 for juveniles and adults respectively. These values are much higher than previously reported for this species being fed smaller sized cultured microalgae. Our results strongly suggest that the difficulties in the nursery and broodstock hatchery culture of this oyster may be due to inappropriate phytoplankton diets. We recommend the provision of cultured microalgae of 20-75 μm in diameter for improving the performance of hatchery maintained juvenile and adult O. chilensis.     

Effects of α-lipoic and ascorbic acid on the muscle and brain fatty acids and antioxidant profile of the South American pacu Piaractus mesopotamicus

The effects of dietary α-lipoic acid (LA) and vitamin C on the fatty acid (FA) composition in the brain and muscle and vitamins E and C levels in the brain were studied in the fish Piaractus mesopotamicus. A two-factorial design, where diets were devoid or supplemented with ascorbate (500 mg AA kg^− 1) and/or lipoic acid (1000 mg kg^− 1), was used. The levels of eicosapentaenoic acid (20:5n − 3, EPA) increased (P < 0.01) in muscle polar lipids (PL) in LA groups (6.93% ± 0.43 vs. 5.83% ± 0.40 and 6.68% ± 0.53 vs. 6.00% ± 0.39), and the same trend was also seen in the brain, however not significant. These changes are suggested to be caused by a change in lipid metabolism rather than being a direct effect of protection by LA against lipid peroxidation. No interaction of vitamin C and LA neither effects of LA on vitamin E (15.1-19.2 mg α-tocopherol g^− 1 tissue) or vitamin C (total AA, 41.7-89.8 μg g^− 1 tissue) in brain was detected.     

Effect of temperature and photoperiod on the growth, feed consumption, and biochemical content of juvenile green abalone, Haliotis fulgens, fed on a balanced diet

Juvenile green abalone, Haliotis fulgens (31.3 ± 0.1 mm, 3.7 ± 0.04 g live weight) were reared in laboratory for six months in order to determine their survival, growth, tissue composition, feed consumption (C), feed conversion ratio (FCR) and protein efficiency ratio (PER) under two temperatures (20 °C and 25 °C) and three photoperiods (00:24, 12:12 and 24:00 light:dark hours). Survival was ca. 100% at 20 °C, and between 68% and 75% at 25 °C. The highest gross growth rate (109 ± 4.3 μm d^− 1, 69 ± 3.9 mg d^− 1) was observed in abalone from the combination 20 °C-00:24 L:D. Slowest GGR (38 ± 4.1 μm d^− 1, 26 ± 1.5 mg d^− 1) was observed in the combination 25 °C-24:00 L:D. Organisms from 25 °C exhibited signs of the withering syndrome at the end of the experiment. Gross energy content (4.4 to 4.6 kcal g^− 1 tissue dry wt, TDW) and crude protein (60 to 68% TDW) were not significantly affected by either temperature or photoperiod, but organisms from 20 °C exhibited lower moisture content (86.8 to 88.6%) and higher tissue:shell ratio (0.34-0.40) than those from 25 °C (88.9 to 92.1%; 0.22-0.31 respectively). Feed consumption markedly increased at night, decreased with age, and was higher at 25 °C than 20 °C, irrespective of photoperiod. Highest C was observed under continuous darkness (0.66 to 0.95% BW d^− 1 at 20 °C and 0.84 to 1.25% BW d^− 1 at 25 °C), and was lowest under continuous light (0.50 to 0.82% BW d^− 1 at 20 °C and 0.71 to 1.02% BW d^− 1 at 25 °C). FCR and PER were both affected by temperature but not by photoperiod. Higher PER (2.2 to 3.4) and lower FCR values (0.69 to 1.05) were observed at 20 °C, when compared to 25 °C (PER 1.35 to 2.09, FCR 1.10 to 1.86). Sex ratios were ca. 1:1 in the 00:24 and 12:12 L:D photoperiods, yet ca. 50% of abalone from the 24:00 L:D photoperiod were immature at the end of the experiment. It is concluded that H. fulgens can be best cultured at 20 °C and 00:24 or 12:12 L:D regimes, while sustained temperatures at or above 25 °C may result in cumulative stress, altered physiological rhythms, and delayed maturation.