Effects of calorie restriction on the expression of manganese superoxide dismutase and catalase under oxidative stress conditions in the rotifer <Emphasis Type="Italic">Brachionus plicatilis</Emphasis>

Calorie restriction (CR) in the rotifer Brachionus plicatilis extends its lifespan, as it enhances the expression of antioxidant enzymes such as manganese superoxide dismutase (Mn SOD) and catalase. Here we show that CR also increased the mRNA levels of these antioxidant enzymes upon exposure to oxidative stress. Rotifers cultured under CR showed a higher survival rate than those fed ad libitum (AL) upon exposure to 0.05–0.2 μM juglone, an oxidative stress inducer. The relative mRNA levels of Mn SOD and catalase before exposure to juglone were slightly higher in the CR rotifers than in their AL counterparts, although these differences were not statistically significant. AL rotifers showed no apparent upregulation of the mRNA levels of these antioxidant enzymes upon exposure to 0.025 and 0.05 μM juglone. In contrast, the CR rotifers increased the mRNA levels of Mn SOD and catalase by up to 5.4-fold and 4.2-fold, respectively, resulting in significant differences between their levels in AL and CR rotifers under oxidative stress conditions. Furthermore, the protein level of catalase was clearly higher in CR than in AL rotifers 6 h after exposure to oxidative stress. These results suggest that the upregulation of Mn SOD and catalase genes is involved in CR-induced resistance to oxidative stress in the rotifer.     

Effects of astaxanthin on Brachionus manjavacas (Rotifera) population growth

Astaxanthin is a red secondary carotenoid and powerful antioxidant that is used in aquaculture to enhance colour and improve fish health. Brachionid rotifers are often used as a live feed for larval fish, but do not contain endogenous carotenoids. However, they can be enriched with astaxanthin through their diet and transfer it to larval predators. When supplemented with 2 μg/ml astaxanthin oleoresin extracted from the green alga Haematococcus pluvialis, Brachionus manjavacas rotifer cultures reached significantly higher population densities and maintained them for longer. Furthermore, data are presented that exposure to oleoresin or pure astaxanthin enhances rotifer resistance to oxidative stress, a common cause for the collapse of rotifer mass cultures. Astaxanthin can be visualized in the gut of the rotifers, allowing the time course of uptake to be estimated by image analysis. Using this method, it was found that accumulation of astaxanthin in the rotifer gut saturates after 1.5 hr of exposure. The bioactive dose of astaxanthin oleoresin for rotifers was found to be 1–20 μg/ml. Astaxanthin concentration in rotifer tissues was measured using absorbance spectrophotometry. It was found that treating rotifers with 20 μg/ml for 24 hr; the concentration of astaxanthin absorbed into rotifer tissues was 2.6 mg/g. Overall, these experiments indicate that astaxanthin extracted from H. pluvialis can be used to improve the productivity and stability of rotifer mass cultures by increasing oxidative stress resistance and enhance the nutritional content of rotifers for larval fish.     

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

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

A comparison of the growth and survival of two freshwater crayfish species, Astacus leptodactylus Eschscholtz and Pacifastacus leniusculus (Dana), under different temperature and density regimes

Growth experiments carried out with two juvenile crayfish species, Astacus leptodactylus Eschscholtz and Pacifastacus leniusculus (Dana), at different temperatures and densities highlighted the problem of cannibalism under conditions aimed at intensifying crayfish production. Cannibalism proved to be much lower in A. leptodactylus than P. leniusculus, suggesting that the former might be the better candidate for astaciculture. In the first of two population survival trials, A. leptodactylus showed a higher survival rate than P. leniusculus, with 26% of P. leniusculus surviving in the first replicate, compared to 42.3% of P. leniusculus, and 40.76% surviving in the second replicate, compared to 47.6% of P. leniusculus. The same trend was observed in the second experiment, with P. leniusculus showing survival rates of 48.5 and 55.3% (first and second replicates, respectively) in comparison to 65.2 and 68.2%, respectively, for A. leptodactylus. It is therefore highly likely that if P. leniusculus were to become established in Turkey, it would outcompete the native A. leptodactylus even if it were not to be devastated by the crayfish plague that has decimated the native species. The experiments also highlighted the problem of differential growth, with some juveniles hardly growing at all while others reached a relatively large size. The range in carapace length (CL) was 9–18 mm for A. leptodactylus and 8.5–18.5 mm CL for P. leniusculus at the end of the first experiment. While both species grew quickly, P. leniusculus hatched earlier, giving it an advantage over A. leptodactylus; consequently, by the end of the summer, the juveniles of the former were larger than those of A. leptodactylus. Specific growth rate values showed that the juveniles of the two species had similar growth rates. The results also revealed that growth was not significantly affected by density in both species at 15°C, but at 25°C, growth was significantly better at a density of 234 juveniles m⁻² than at 468 juveniles m⁻², and better at 468 juveniles m⁻² than at 937 juveniles m⁻² (P < 0.01 and P < 0.001, respectively). We conclude that P. leniusculus is a good candidate for aquaculture as it has a rapid growth rate and early hatching and maturity; however, its aggressive behavior may make it a less attractive proposition than A. leptodactylus, which is also fast growing but less aggressive. This study is a part of PhD study of M.M. Harlıoğlu, who is supported by Fırat University Elazığ, Turkey.     

Comparative growth of Pacific oyster (Crassostrea gigas) postlarvae with microfeed and microalgal diets

Two trials were carried out in the laboratory in order to assess the effect of microparticulated feed (F) and live (Thalassiosira pseudonana, M) diets on the growth of recently set (396 ± 13 μm shell height) and 2 mm Crassostrea gigas postlarvae. Different proportions of M and F (100:0, 75:25, 50:50; 25:75, 0:100) were delivered in a single dose of 3 h d⁻¹ in trial 1. Dietary M:F proportions of 100:0, 50:50, and 0:100 were delivered as a single pulse of 8 h d⁻¹ (P1) or two pulses of 4 h⁻¹ (P2) in trial 2. Maximal daily M ration was 296 cells μl⁻¹ d⁻¹ (trial 1), 150 M cells μl⁻¹ d⁻¹ (trial 2), or their equivalent F dry weight. Shell height (SH), dry (DW), and organic weight (AFDW) were evaluated weekly. Oysters from trial 1 significantly increased their size after 28 days, and exhibited no significant dietary differences in terms of DW (1.21 ± 0.15 to 2.01 ± 0.28 mg) or AFDW (0.091 ± 0.022 to 0.166 ± 0.029 mg). Newly set postlarvae (trial 2) also exhibited significant growth after 25 days. No dietary differences were observed in trial 2, yet P2 oysters attained significantly higher shell heights (825–912 μm) than P1 oysters (730–766 μm) after 25 d. Pulse effects were marginally not significant in terms of AFDW and growth rate. Together, these findings showed that balanced microfeeds have a practical potential for the culture of early C. gigas postlarvae, when they are delivered in pulse-feeding schemes     

Influence of dietary <Emphasis Type="SmallCaps">l</Emphasis>-selenomethionine exposure on the survival and osmoregulatory capacity of white sturgeon in fresh and brackish water

Near simultaneous exposure to selenium and salinity stress is an environmental reality faced by white sturgeon juveniles in the San Francisco Bay-Delta, having the potential for adverse synergistic impacts on juveniles during seaward migration. White sturgeon juveniles (36–132 g) were transferred into higher salinities (15–20 ppth) after exposure to dietary selenium (0.4, 9.6, 20.5, 41.7, 89.8, or 191.1 μg Se/g diet) in the form of l-selenomethionine (SeMet) for 8 weeks in freshwater (0 ppth). White sturgeon fed above 41.7 μg Se/g diet experienced significant (P < 0.05) declines in survival relative to sturgeon fed between 0.4 and 41.7 μg Se/g diet when transferred into brackish water (15 ppth salinity) for 3 days. Plasma osmolality and ionic concentrations in white sturgeon after abrupt transfer correlated positively with dietary Se concentrations. Transfer of white sturgeon fed above 41.7 μg Se/g diet into 20 ppth brackish water for 1 day resulted in significant declines in survival relative to white sturgeon fed 0.4–41.7 μg Se/g diet. Hematocrit and dehydrational weight loss were significantly correlated with dietary Se concentrations while plasma osmolality and ion concentrations were not. The transfer of sturgeon into 20 ppth water for 3 days resulted in severe survival declines in all treatment groups. The results of this study suggest that the previously established threshold for Se toxicity (10–20 μg Se/g) is sufficient to protect white sturgeon from the adverse interactive affects resulting from increases in dietary Se and ambient water salinity.     

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.     

Comparing the efficacy of dietary α-tocopherol with that of dl-α-tocopheryl acetate, both either alone or in combination with ascorbic acid, on growth and stress resistance of angelfish, Pterophylum scalare, juveniles

This study aimed to compare the efficacy of dietary α-tocopherol with that of dl-α-tocopheryl acetate, both either alone or in combination with vitamin C (ascorbic acid), on the growth performance, survival, and stress resistance of angelfish, Pterophylum scalare, juveniles. Juveniles were fed ad libitum for four weeks with Artemia enriched with no vitamins (control), vitamin C (T_c), α-tocopherol (T_α), dl-α-tocopheryl acetate (T _dl ), α-tocopherol and vitamin C (T_α+C), and dl-α-tocopheryl acetate and vitamin C (T _dl+C). After four weeks, an osmotic stress test was performed using seawater (25 g/L) to evaluate juvenile’s resistance to stress. Whole-body glucose and cortisol were used as stress indicators. At the end of the feeding trial, growth performance and survival of the juveniles fed vitamin-enriched Artemia were significantly (P < 0.05) higher than for the control fish. Best performance was recorded for the T_α+C group. Survival, however, was not significantly (P > 0.05) different between the vitamin-fed groups. Osmotic stress significantly elevated the stress indicators, whole-body cortisol and glucose levels (P < 0.05), highest and lowest values being observed in control and T_α+C groups, respectively. Survival after osmotic stress of juveniles fed the T_α+c diet was significantly higher (by 46.2%, P < 0.001) than for controls. Results suggested that α-tocopherol has greater efficacy than dl-α-tocopheryl acetate and enriching Artemia with α-tocopherol and vitamin C together improves growth performance, survival, and stress resistance of angelfish juveniles.     

Effect of gamma-aminobutyric acid and porcine growth hormone on survival of the euryhaline rotifers <Emphasis Type="Italic">Brachionus plicatilis</Emphasis> sp. complex preserved at low temperature

Gamma-aminobutyric acid (GABA) at 50 μg/ml and porcine growth hormone (GH) at 0.025 IU/ml were tested to see whether these chemicals would reduce the stress experienced by euryhaline rotifers Brachionus plicatilis species complex (L-, S- and SS-morphotypes) during low temperature (4–12°C) storage. Rotifers cultured at 25°C were transferred to 4–12°C for 10–30 days and transferred back to 25°C for recovery. GABA or GH were added to the rotifers at three different time points: 6 h before transfer from 25°C to low temperature (6h−), on day 7 after preservation at low temperature (7d+) and on the first day of recovery. For L-type rotifers, the GH treatment before the transfer to 4°C for 30 days was effective for better survival, while the GABA treatment was most effective for the S-type preserved at 10°C for 14 days. For the SS-type, the chemical treatments were not effective when the rotifers were preserved at 12°C for 14 days. After low temperature preservation, GABA treatments with the S- and SS-type rotifers just after their transfer to 25°C induced a relatively faster recovery of the rotifer population.     

Difference Between Tetrodotoxin and Saxitoxins in Accumulation in Puffer Fish Takifugu rubripes Liver Tissue Slices

In vitro accumulation of tetrodotoxin (TTX) and paralytic shellfish toxin (PST) in tiger puffer fish Takifugu rubripes was investigated using liver tissue slices. When T. rubripes liver slices were incubated with Leibovitz’s L-15 medium containing 0.13 mM TTX at 20 °C in air with saturated humidity, they accumulated 21.5 ± 7.3 μg TTX g⁻¹ liver after the incubation for 12 h and increased to 55.3 ± 8.2 μg TTX g⁻¹ liver at 48 h. In the incubation of T. rubripes liver slices with 0.13 mM PST-containing medium, PST was detected 6.3 ± 0.9 μg g⁻¹ liver at 12 h and reached a plateau thereafter. These results reveal the difference between TTX and PST in accumulation in T. rubripes liver tissue slices. To examine the variation in PST accumulation among fish species, the liver tissue slices from tiger puffer fish T. rubripes, parrot-bass Oplegnathus fasciatus and green ling Hexagrammos otakii were incubated at a concentration of 0.027 mM PST. The toxin contents of 3.0 μg g⁻¹ liver were observed at 8 h regardless of fish species but were not increased subsequently, showing no variety among these three species as to accumulation patterns of PST. It is noted that the tiger puffer fish T. rubripes liver specifically accumulate TTX in preference to PST.     

Induction of larval metamorphosis in the sea cucumber Apostichopus japonicus by neurotransmitters

Larval metamorphosis inducers of the sea cucumber Apostichopus japonicus were screened from physiologically active compounds. Doliolaria larvae completed their metamorphosis to juveniles in 120 h when treated with 5–10 μM of dopamine and l-DOPA, and 50 μM of l-adrenaline and l-noradrenaline. Doliolaria larvae had to be exposed to dopamine or l-DOPA for at least 24 h. D1-like dopamine receptor antagonists SKF87566 and LE300 (10 μM) inhibited metamorphosis by dopamine. However, the D2-like dopamine receptor antagonists sulpiride and nemonapride (10 μM) did not inhibit the effect of dopamine. The results suggest that D1-like dopamine receptors are involved in larval metamorphosis of the sea cucumber A. japonicus.     

Development of larval culture techniques for the shore crab, <Emphasis Type="Italic">Carcinus maenas</Emphasis> (L)

The shore crab Carcinus maenas is a commercially important species, utilised as sea angling bait as well as supporting a European-wide fishery. Hatchery production could provide an alternative source of bait crabs, alleviating potential competition between these sectors and environmental concerns regarding bait collection practices. A series of experiments were carried to investigate the potential for hatchery production, focusing on effects of dietary regimes and stocking densities through the zoeal stages and the influence of tank substrates and stocking density during the megalopa stage. Inclusion of the rotifer Brachionus plicatilis as live food for early larval stages conveyed no advantage in terms of survival or rate of development compared to a diet of Artemia nauplii. Increasing zoea stocking densities (from 94 to 557 l⁻¹) had a significantly negative effect upon survival to the megalopa stage (from 75% down to 47%), although this was off-set by a significant increase in production, with 260 megalopae⁻¹ produced from an initial density of 557 zoeae l⁻¹. The inclusion of substrates for megalopa stages had no impact on production or development rate, compared to tanks with no substrate. The completely benthic behaviour of megalopae indicates that tank floor area will be a limiting factor for crab production. Increasing stocking density of megalopae was found to significantly and negatively influence survival, although above 10,000 megalopae m⁻² the rate of decline in survival stabilised and maximum production (3,114 juveniles m⁻²) of juvenile crabs could be achieved at the highest stocking densities tested (40,000 m⁻²).     

Effects of temperature and salinity on oxygen consumption and ammonia excretion of juvenile miiuy croaker, <Emphasis Type="Italic">Miichthys miiuy</Emphasis> (Basilewsky)

The metabolic responses of the juvenile Miichthys miiuy in terms of oxygen consumption and ammonia excretion to changes in temperature (6–25°C) and salinity (16–31 ppt) were investigated. At a constant salinity of 26 ppt, the oxygen consumption rate (OCR) of the fish increased with an increase in temperature and ranged between 133.38 and 594.96 μg O₂ h⁻¹ g⁻¹ DW. The effect of temperature on OCR was significant (P < 0.01). Q₁₀ coefficients were 6.80, 1.41, 1.29 and 2.36 at temperatures of 6–10, 10–15, 15–20 and 20–25°C, respectively, suggesting that the juveniles of M. miiuy will be well adapted to the field temperature in the summer, but not in the winter. The ammonium excretion rates (AER) of the fish were also affected significantly by temperature (P < 0.01). The O:N ratio at temperatures of 6, 10, 15 and 20°C ranged from 13.12 to 20.91, which was indicative of a protein-dominated metabolism, whereas the O:N at a temperature of 25°C was 51.37, suggesting that protein-lipids were used as an energy substrate. At a constant temperature of 15°C, the OCRs of the fish ranged between 334.14 (at 31 ppt) and 409.68 (at 16 ppt) μg O₂ h⁻¹ g⁻¹ DW. No significant differences were observed in the OCR and AER of the juveniles between salinities of 26 and 31 ppt (P > 0.05). The OCR and AER at 16 ppt were, however, significantly higher than those at 26 and 31 ppt (P < 0.05), indicating salinity lower than 16 ppt is presumably stressful to M. miiuy juveniles.     

Myxosporean and microsporidian infections in cultured Pacific bluefin tuna <Emphasis Type="Italic">Thunnus orientalis</Emphasis> in Japan

During the parasitological survey of cultured juvenile Pacific bluefin tuna (PBT) Thunnus orientalis in 2007 and 2008, two myxosporeans and one microsporidian were found. Morphological and molecular analysis showed that the heart-infecting and brain-infecting myxosporeans are identified as Kudoa shiomitsui and K. yasunagai, respectively. This is a new host record for both species. High prevalence of infection (77–100%) with K. shiomitsui was observed in October to December (1–2 months post-transfer to sea cages), whereas only a few fish were infected with K. yasunagai. A microsporidian observed as white “cysts” in the trunk muscle of PBT had a resemblance to Microsporidium seriolae, the causative parasite of beko disease in yellowtail. Phylogenetic analysis showed that the microsporidian from PBT is closely related to but distinct from several other muscle-infecting species such as M. seriolae, Microsporidium sp. RSB, and Microsporidium sp. SH. Additionally, the spore dimension (2.7 × 1.5 μm on average) was remarkably smaller than the others. These results suggest that the present microsporidian is an undescribed species and designated Microsporidium sp. PBT. Prevalence and intensity of infection with Microsporidium sp. PBT reached a maximum of 100% and 20 cysts/fish, respectively. Although pathogenic effects of the two Kudoa species on fish health remain unknown, the microsporidian could be of concern to PBT aquaculture due to unsightly cysts in the musculature, reducing the market value of the fish.     

Effects of dietary microalgal species and hormone treatment on the lorica size and reproductivity of heavy-ion beam irradiated rotifers

In aquatic seeding production, the feeding regime of fish larvae consists of rotifers to Artemia, while there is a lack of intermediate-sized feed in the range of 350–600 µm. To solve this problem, in our previous study, the euryhaline rotifer Brachionus plicatilis (L-type, Notojima strain) were irradiated with carbon heavy-ion-beams, and large-sized rotifer mutant lines (>?350 µm lorica length) were established. This study aimed to enhance the mutated morphometric characteristics and reproductivity through the combined use of three microalgal species (Nannochloropsis oculata, Tetraselmis tetrathele, and Chlorella vulgaris), and two hormones [juvenile hormone (JH) and gamma-aminobutyric acid (GABA)]. The combination of T. tetrathele and JH was effective in enhancing the mutated phenotype, and the largest lorica length of 344–425 µm was observed with no significant differences in population growth between the wild-type and mutant strains. The combination of N. oculata and GABA enhanced the population growth of the mutant line, and its growth rate was 2.4 times higher than that of the control group (without GABA). This study indicates that the morphometric characteristics and reproductivity of rotifer mutant lines could be regulated by feed and hormone supplementation. These findings can promote the efficient use of mutant rotifer lines in aquaculture facilities.

     

Perkinsus mediterraneus infection induces oxidative stress in the mollusc Mimachlamys varia

Perkinsus mediterraneus is a protozoan parasite that can cause marine mollusc diseases known as perkinsosis being a serious threat for clam cultures worldwide. The aim of the present study was first to determine the Perkinsus species infecting the variegated scallop Mimachlamys varia and then to evaluate the existence of oxidative stress in gills of M. varia according to different degrees of infection. DNA sequencing confirmed that P. mediterraneus was the species infecting M. varia. ROS production was progressively increasing with the degree of infection although the differences were only significant in the high-infected group. Low degree of infection significantly increased superoxide dismutase (SOD) and glutathione S-transferase (GST) activities and nitrite levels with respect to the control group. In the high-infected group, a significant increase was evidenced in all analysed enzymes, catalase, SOD, glutathione reductase and GST. Non-significant differences in MDA levels were observed between the control and low-infected groups; however, a significant increase in MDA levels was observed in the high-infected group. In conclusion, the infection by Perkinsus mediterraneus in M. varia induces oxidative stress and an antioxidant response directly related to the infection degree that can contribute to the pathogenicity of the infection.     

Enhancement of <Emphasis Type="Italic">Penaeus monodon</Emphasis> shrimp postlarvae growth and survival without water exchange using marine <Emphasis Type="Italic">Bacillus pumilus</Emphasis> and periphytic microalgae

We have investigated the possibility of using a consortium of marine bacterium and periphytic microalgae to improve the water quality and increase the growth and survival of the shrimp Penaeus monodon in a hatchery system. Three treatments were evaluated for their effect on P. monodon postlarvae (PL) when the culture water was not changed: Bacillus pumilus alone (B); periphytic microalgae alone (M); B. pumilus + periphytic microalgae (BM). P. monodon PL raised in a tank of unchanged water without bacterium and periphytic microalgae served as the control. The water in tanks of the M and BM treatments had significantly low levels of total ammonia-nitrogen (TAN) (0.03 and 0.01 mg l⁻¹, respectively) and nitrite-nitrogen (NO₂-N) (0.03, 0.01 mg l⁻¹, respectively) than that in the B (TAN 0.80, NO₂-N 0.68 mg l⁻¹) and control (TAN 1.11, NO₂-N 1.12 mg l⁻¹) tanks. Moreover, PL cultured in tanks M and BM had significantly higher survival and specific growth rates and a significantly higher resistance to the reverse salinity stress test than those in the B and control tanks. Compared to the control PL, the PL cultured in the BM tanks had significantly higher levels of protein, lipid, polyunsaturated fatty acids, ecosapentaenoic acid, and docosahexaenoic acid. The culture water in tanks BM also contained significantly less Vibrio than the control water. Our results illustrate the beneficial effects of a B. pumilus and periphytic microalgae consortium on improving the water quality and the growth and survival of shrimp PL grown in a hatchery system.     

Rotifer community structure in fish‐farming systems associated with a Neotropical semiarid reservoir in north‐eastern Brazil

The study was conducted to assess the community structure of planktonic rotifers and their relation to the environmental impact of Nile tilapia, Oreochromis niloticus (Linaeus, 1758), aquaculture activities (ponds and net‐tanks), associated with a Neotropical semiarid reservoir in Brazil. Our hypothesis was that the ecological attributes of the rotifer community were different when considering the influence of fish aquaculture activities. We identified 28 species, with 10 species from the Brachionidae family. The average density and diversity index of rotifers were higher in reservoir stations, with mean values in the ponds approximately 50% lower than those of the reservoir. The microphagous species dominated during all the time, while the raptorial species were accidental in all studied environments. The ponds were represented by four significant indicator species: Brachionus caudatus, B. leydigi, Dicranophoroides caudatus and Testudinella patina and the reservoir by three: B. falcatus, B. havanaensis and Conochilus dossuarius. In general, nine species were significantly associated with some categories of environmental conditions, such as high or low turbidity and low values of conductivity and TDS. Four of the five best bioindicator species belonged to the microphagous genus Brachionus. B. havanaensis indicated five environmental conditions (IndVal > 93.1%), and it appeared to be a key species in this Neotropical semiarid reservoir influenced by aquaculture activities. The dominance of microphagous rotifers suggests a functional redundancy of species in the studied environments. We found that these systems and their management affected the planktonic rotifer community in this region of Brazil by increasing the species richness.     

Application of α-glucosidase activity and drug susceptibility tests to epidemiological studies on the fish pathogen <Emphasis Type="Italic">Nocardia seriolae</Emphasis>

This study determined the minimum inhibitory concentrations (MICs) for oxytetracycline hydrochloride (OTC) and erythromycin (Em), along with the α-glucosidase (α-glu) activities in 110 Nocardia seriolae strains isolated in Miyazaki and Kagoshima prefectures in 2008–2009. The strains were examined for the presence of the tet(K), tet(L), tet(M), tet(O), tet(S), erm(A), erm(B), mph(A), mef(A), and msr(D) genes. All the α-glu-positive strains (n = 15) were OTC resistant and Em sensitive, with MICs of 32–64 and <0.125 μg/ml, respectively. All the α-glu-negative strains (n = 95) were OTC sensitive, with MICs of 2–4 μg/ml, and most of them (93 of 95) were Em resistant, with MICs of >128 μg/ml. The MICs for Em in the remaining 2 α-glu-negative strains were <0.125 μg/ml. The 15 OTC-resistant strains possessed the tet(K) and/or tet(L) gene(s), and all of the 93 Em-resistant strains possessed both the mef(A) and msr(D) genes. The relationship between α-glu activity and drug sensitivity of the N. seriolae strains may explain the difference in prevalence of each phenotype. Nevertheless, the relationship should be further explored using N. seriolae isolates collected from more prefectures and farms.