Cholesterolaemia and triacylglycerolaemia in farmed rainbow trout,Oncorhynchus mykiss

Physiological (reference) value intervals determined by the lower 2.5% and upper 97.5% quantiles were calculated for blood plasma cholesterol (CHOL) and triacylglycerol (TGL) in farmed rainbow trout, Oncorhynchus mykiss, in raceway culture. The fish were given dry pelleted diets that contained 37–47% crude protein and 7–14% crude fat and were kept at a stocking density of 50 kg m^?3 in tanks provided with running freshwater at an ambient temperature of 3–16°C and dissolved oxygen, 8.4–11.5 mg L^?1. Blood was sampled between September and November at a photoperiod of 9:00–13:00 hours: 11:00–15:00 hours (light:dark). Cholesterol levels were significantly (P = 0.0001) greater in males (4.7–12.1 mmol L^?1, n = 34, mean weight 406 ± 138 g) than immature females (3.2–9.7 mmol L^?1, n = 386, mean weight 416 ± 147 g). Physiological range for TGL in immature females and males was 2.4–14.4 mmol L^?1 (n = 249, mean weight 418 ± 149 g). The distribution and density of the quantiles in the tested reference group were made possible by the use of histograms, which showed normal distributions for CHOL in males and in females, but not for TGL, in which a sinistral asymmetry was found. Correlation and regression analyses indicated significant (P = 0.0000) dependence between the CHOL and total protein (r² = 76.2%), CHOL and Fulton's condition factor (r² = 43.3%) and CHOL and absolute weight of liver (r² = 45.5%). Fluctuation in cholesterolaemia and triacylglycerolaemia, depending on nutrition and the aquaculture method is discussed below.     

Isolation and culture of the marine rotifer, Colurella dicentra (Gosse, 1887), from a Mississippi Gulf Coast estuary

Few marine rotifer species (e.g. Encentrum linheii and Synchaeta cecilia) have been cultured successfully besides Brachionus plicatilis and B. rotundiformis, commonly used to rear larvae of many marine fish species. The development of culture techniques for marine rotifers smaller in size than the Brachionus species may be useful for rearing fish species for which the currently used prey are too large. We evaluated the possibility of culturing Colurella dicentra isolated from a Mississippi Gulf Coast estuary. An experiment was conducted to determine the effects of salinity (10–35 g L^?1) on its population growth rate. Rotifers were fed Nannochloropsis oculata at a density of 100 000 cells mL^?1 for 15 days. Colurella dicentra survived in water with a salinity of 10–47 g L^?1. Densities of up to 300 rotifers mL^?1 were sometimes attained in cultures. Salinity influenced C. dicentra production (P<0.001). The mean rotifer numbers at 10 g L^?1 (22 840±2604 SD), 15 g L^?1 (25 980±7071 SD) and 20 g L^?1 (19 780±1029 SD) at the end of the experiment were similar (P>0.05), but were higher (P=0.05) than numbers at 25 g L^?1 (4240±1783), 30 g L^?1 (1300±264 SD) and 35 g L^?1 (100±101 SD). The population growth rate (r) of the rotifers was the highest at 15 g L^?1 (0.37–0.42 day^?1), and the lowest at 35 g L^?1 (?0.33–0.06 day^?1). This is the first report of C. dicentra in the estuarine waters of the Gulf of Mexico, and also the first time it has been cultured successfully.     

Red blood cell indices of rainbow trout Oncorhynchus mykiss (Walbaum) in aquaculture

A direct non‐parametric method was used to calculate reference (physiological) haematology values for farmed 10–12‐month rainbow trout of the Kamloops strain (mean weight: 330±131 g) with respect to red blood cell counts (RBCc), haematocrit values (Hct), haemoglobin concentrations (Hb), mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH) and mean corpuscular haemoglobin concentrations (MCHC). The fish in the selected reference group (n=798) were given dry pelleted diets that contained 37–47% crude protein, 7–18% crude fat and 108–300‐mg vitamin E, 1.08–5‐mg folic acid, 0.018–0.05‐mg vitamin B₁₂, 48–64.5‐mg iron, 4.5–8.4‐mg copper and 0.18–0.24‐mg selenium supplied per kg of diet. Ethoxyquin and butylhydroxytoluol were used to protect the fat component against oxidation. The fish were kept at a stocking density of 50kg per cubic metre in tanks provided with running freshwater (dissolved oxygen 8.4–11.5 mg L^?1, with O₂ saturation of 77–98%) at an ambient temperature of 0.2–16°C. Blood was sampled between September and November at a photoperiod of 9–13 h:11–15 h (light:dark). Reference ranges for the preceding haematological indices were as follows in immature females (males): RBCc, 0.77–1.42T L^?1 (T – tera, 10¹²) (0.98–1.55T L^?1); Hct, 0.304–0.502 (0.34–0.546); Hb, 54–93 g L^?1 (59–97 g L^?1); MCV, 282–469 fL (279–434 fL); MCH, 51–86 pg (47–78 pg); MCHC, 0.15–0.22 (0.15–0.2). In males, values for RBCc, Hct and Hb were significantly higher (P=0.01 and 0.0000 respectively) and those for MCV, MCH and MCHC were significantly lower (P=0.01 and 0.0002 respectively) than in immature females. Nutritional and environmental factors affecting erythropoiesis in trout and some correlations between haematological (RBCc, Hb, Hct) and biochemical indices of the blood plasma (total protein, cholesterol) are discussed.     

Effect of recovery salinity on survival of acutely stressed halibut (Hippoglossus hippoglossus L) larvae

First‐feeding halibut larvae (245‐day degrees; 40 days post hatch), reared at 34 g L^?1 salinity and 7°C, were subjected to handling and allowed to recover in a range of salinities (0–34 g L^?1) and at 10°C. Survival of the unfed larvae was determined daily for 18 days. Mortality rates approached 0 after 4 days in all treatments and presumed starvation‐induced mortality started at about 11 days post handling. By 20 days post treatments, all larvae had died. Salinities in the range of 10–20 g L^?1 produced significantly (anova , P<0.01) higher initial survival (71–95%) than salinities above 20 g L^?1 (24–48%) or below 10 g L^?1 (0–19%) and this survival pattern changed little in unfed larvae for the first 10 days following the stressor. For example, 24 hour post handling, survival of halibut was improved from 28.7±16.5% (mean±standard error, n=3) at 34.0 g L^?1 to 95.2±4.8% at 13 g L^?1. A second‐order polynomial regression of 4‐day post‐handling survival data (y=?0.002x ²+0.0603x+0.0699, r²=0.3936) predicted a maximum survival at 15.1 g L^?1 salinity. These results have important implications for halibut aquaculture and research when handling of larvae is unavoidable. For practical applications, we recommend reducing salinity of receiving waters to 15–20 g L^?1 with a slow (3–4 days) reacclimation to ambient conditions.     

Seminal plasma composition and its relationship with physical spermatological parameters of Grass carp (Ctenopharyngodon idella) semen: with emphasis on sperm motility

In this research, the mineral and organic composition of the seminal plasma, physical spermatological parameters and their physiological relationships were investigated in grass carp (Ctenopharyngodon idella). The seminal plasma contained 98.14±5.23 mM L^?1 (Na⁺), 380.85±25.95 mM L^?1 (K⁺), 30.25±4.96 mg dL^?1 (Ca²⁺), 19.16±1.70 mEq L^?1 (Mg²⁺), 1.36±0.11 mg dL^?1 glucose, 0.37±0.08 g dL^?1 total protein, 12.02±1.18 mg dL^?1 cholesterol, 14.85±1.50 mg dL^?1 triglyceride and 43.5±9.56 mg dL^?1 urea. The following spermatological parameters were found: sperm volume 14.44±1.16 mL, sperm motility 80.60±1.55%, movement duration 67.68±4.32 s, density 15.43±0.72 × 10⁹ mL^?1, total density 337.43+45.86 × 10⁹ and pH 7.24±0.17. The Na⁺ and Ca²⁺ ions correlated negatively with spermatozoa motility (r=?0.453, P>0.05 and r=?0.192, P>0.05) respectively. The K⁺ ion correlated positively with spermatozoa motility (r=0.545, P>0.05). But a statistically significant correlation was not observed between sperm motility and seminal plasma parameters. The following correlations were observed between mineral and organic components. The Mg²⁺ was positively correlated with glucose and cholesterol (r=0.692, P<0.05 and r=0.680, P<0.05) respectively. A highly significant positive relationship was also found between Mg²⁺ and total protein (r=0.837, P<0.01). On the other hand, a significantly negative relationship was found between Ca²⁺ and triglyceride (r=?0.639, P<0.05). These parameters should be considered when developing procedures for either artificial fertilization or for cryopreservation of grass carp sperm.     

Effect of dietary inclusion of lysozyme on growth performance and plasma biochemical parameters of rainbow trout (Oncorhynchus mykiss)

This study was conducted to evaluate the effect of dietary lysozyme supplementation on growth performance and plasma biochemical parameters of rainbow trout (Oncorhynchus mykiss). Graded levels of lysozyme [0 (control), 150, 300, 450 and 600 mg kg^?1 diet] were fed to fish (initial average weight 7.76 g) for 10 weeks. Dietary lysozyme supplementation regardless of inclusion level generally improved the growth, feed utilization and nutrient retention, but significant differences were mainly observed between the 450 or 600 mg kg^?1 lysozyme group and the control group. Lysozyme supplementation generally decreased the plasma aspartate aminotransferase and alanine aminotransferase (ALT) activities, but significant difference was only observed in the ALT activity between the 450 mg kg^?1 lysozyme group and the control group. In contrast, lysozyme supplementation generally increased the plasma alkaline phosphatase and lysozyme activities, but significant difference was only observed in the lysozyme activity between the 600 mg kg^?1 lysozyme group and the control group. Lysozyme supplementation generally increased the plasma antioxidant activities of enzymes (including superoxide dismutase, glutathione peroxidase and catalase) and total antioxidant capacity, but decreased the plasma malondialdehyde level. These results suggest that dietary 450–600 mg kg^?1 lysozyme inclusion may improve the growth and non‐specific immune response of rainbow trout.     

Water quality in a serial‐use raceway and its effect on the growth of South African abalone,Haliotis midae Linnaeus, 1758

To quantify the effects of serial‐use of water on abalone growth and feed conversion, this study describes water quality in a serial‐use raceway with seven passes. A flow index of 7.2–9.0 L h^?1 kg^?1 was estimated as the minimum value at which to grow 60–70 mm Haliotis midae, as weight gain (analysis of variance; F_{6, 14}=13.9, P<0.0001) and feed conversion ratio (Kruskal–Wallis test; H_{6, 21}=16.3, P=0.012) were significantly reduced at lower values. pH and dissolved oxygen concentration were positively correlated with the flow index (pH, r²=0.99; P<0.001; dissolved oxygen, r²=0.99; P<0.001), while free ammonia nitrogen (FAN) and nitrite were negatively correlated with the flow index (FAN, r²=0.99, P<0.001; Nitrite, r²=0.93, P<0.001). The concentration of nitrite increased throughout the experiment and may reflect the colonization of Nitrosomonas bacteria as water re‐use increased. Based on comparisons with growth and toxicity tests, it is suggested that low pH combined with growth‐limiting levels of FAN were the first variables limiting abalone growth in the serial‐use raceway.     

Determination of microbial community structures of shrimp floc cultures by biomarkers and analysis of floc amino acid profiles

Simple, rapid and reliable methods are required to monitor the microbial community change in aquatic pond for better animal performance. Four floc (suspended organic matter) samples were collected from outdoor raceways and tanks used for culturing Pacific white shrimp Litopenaeus vannamei. Twenty‐two chlorophyll (Chl) and carotenoid pigments were separated, identified and quantified using high‐performance liquid chromatography–ultraviolet/Vis‐mass spectrometry in the freeze‐dried floc samples. Algal community composition (diatoms, chlorophytes, cyanobacteria, dinoflagellates and cryptophytes) was determined by measuring concentrations of the respective taxonomic biomarkers (carotenoid fucoxanthin, lutein, zeaxanthin, peridinin and alloxanthin) as independent variables and Chl a as the dependent variable using a multiple regression model. This analysis found that the phytoplankton community of the floc samples from two groups of shrimp tanks (32 g L^?1‐salinity) were diatom‐dominated (81.7% and 84.4%); and two floc samples from shrimp raceways (5 and 18 g L^?1‐salinity) were chlorophyte‐dominated (75.4% and 82.3%). Assessment of total algal and bacterial biomass by quantification of Chl a and muramic acid, respectively, indicated that the 18 g L^?1‐salinity raceway sample was bacteria‐dominated, whereas the other three floc samples were algae‐dominated. Sample protein quality was evaluated by its essential amino acid (AA) score and index. Arginine and lysine were found to be the two most limiting AAs for all floc samples.     

Short-term responses of adult kuruma shrimp Marsupenaeus japonicus (Bate) to environmental salinity: osmotic regulation, oxygen consumption and ammonia excretion

The effects of salinity on haemolymph osmolality, oxygen consumption and ammonia excretion were investigated in adult kuruma shrimp, Marsupenaeus japonicus (Bate), at salinities of 20, 25, 30 and 35 g L^?1. Haemolymph osmolality showed a positive linear relationship (r²=0.9854) with medium osmolality. The isosmotic point calculated from this relationship was 1039 mOsm kg^?1, which corresponds to a salinity of approximately 35 g L^?1. The slope of the regression equation was very high (0.81), suggesting that M. japonicus adults are poor osmoregulators compared with the adults of other penaeids and to conspecific young. The difference between haemolymph and medium osmolality (D_OP) was lowest at 35 g L^?1 and highest at 20 g L^?1. Thus, the minimum D_OP coincided with the isosmotic point of the shrimp. The respiration rate was significantly lower at 30 g L^?1 than at the other salinities. Ammonia excretion rates were inversely related with salinity and therefore were minimal at 35 g L^?1. The results of this study suggest that the optimum salinity for adult kuruma shrimp is around 30–35 g L^?1 and that even minor (e.g. 5 g L^?1) deviations from this optimum cause significant physiological changes. Further, the observed increases in oxygen consumption and ammonia excretion during exposure to low salinities, which indicate higher energy expenditure and amino acid catabolism for osmoregulation, respectively, suggest that the growth efficiency of M. japonicus adults may be severely compromised by hypohaline water inflow into the rearing ponds.     

Effect of crude oil extracts from trout offal as a replacement for fish oil in the diets of the Australian native fish Murray cod Maccullochella peelii peelii

The efficacy of trout oil (TO), extracted from trout offal from the aquaculture industry, was evaluated in juvenile Murray cod Maccullochella peelii peelii (25.4±0.81 g) diets in an experiment conducted over 60 days at 23.7±0.8 °C. Five isonitrogenous (48% protein), isolipidic (16%) and isoenergetic (21.8 kJ g^?1) diets, in which the fish oil fraction was replaced in increments of 25% (0–100%), were used. The best growth and feed efficiency was observed in fish fed diets containing 50–75% TO. The relationship of specific growth rate (SGR), food conversion ratio (FCR) and protein efficiency ratio (PER) to the amount of TO in the diets was described in each case by second‐order polynomial equations (P<0.05), which were: SGR=–0.44TO²+0.52TO+1.23 (r²=0.90, P<0.05); FCR=0.53TO²–0.64TO+1.21 (r²=0.95, P<0.05); and PER=–0.73TO²+0.90TO+1.54 (r²=0.90, P<0.05). Significant differences in carcass and muscle proximate compositions were noted among the different dietary treatments. Less lipid was found in muscle than in carcass. The fatty acids found in highest amounts in Murray cod, irrespective of the dietary treatment, were palmitic acid (16:0), oleic acid (18:1n‐9), linoleic acid (18:2n‐6) and eicosapentaenoic acid (20:5n‐3). The fatty acid composition of the muscle reflected that of the diets. Both the n‐6 fatty acid content and the n‐3 to n‐6 ratio were significantly (P<0.05) related to growth parameters, the relationships being as follows. Percentage of n‐6 in diet (X) to SGR and FCR: SGR=–0.12X²+3.96X–32.51 (r²=0.96) and FCR=0.13X²–4.47X+39.39 (r²=0.98); and n‐3:n‐6 ratio (Z) to SGR, FCR, PER: SGR=–2.02Z²+5.01Z–1.74 (r²=0.88), FCR=2.31Z²–5.70Z+4.54 (r²=0.93) and PER=–3.12Z²–7.56Z+2.80 (r²=0.88) respectively. It is evident from this study that TO could be used effectively in Murray cod diets, and that an n‐3:n‐6 ratio of 1.2 results in the best growth performance in Murray cod.     

Effect of dietary protein level on the growth and survival of pre-adult freshwater crayfish Cherax quadricarinatus (von Martens) in monosex culture

Feeding trials with five levels of crude protein (CP) (22%, 27%, 33%, 39%, and 45%) and digestible energy ranging from 14.32 to 15.21 kJ g^?1 were carried out to determine optimum dietary protein for the growth and production of pre‐adult freshwater crayfish Cherax quadricarinatus. Triplicate groups of males (ω=23.1±0.58 g) and females (ω=21.8±0.33 g) were fed diets for 70 days in monosex culture. Optimal digestible protein (DP) was estimated for males by fitting mean weight gain to a quadratic model (y=27.86+0.839x–0.0216x², r²=0.945), and a linear model for females (y=32.84–0.0745x, r²=0.959). Optimal male growth occurred with 25.6% CP, equivalent to 19.4% DP. Male crayfish attained significantly higher final weights and absolute growth rate than females fed the 22%, 27%, and 33% CP diets. The results indicated that a 19.4% DP diet, with a P/E ratio of 11.4 mg kJ^?1, produces an optimum growth response for pre‐adult C. quadricarinatus under experimental conditions.     

Aqueous fractionation improves the nutritional value of wheat distillers grains for rainbow trout (Oncorhynchus mykiss)

Fractionation of wheat wet distillers grains (WWDG) was performed to reduce non‐starch polysaccharides (NSP) and increase protein content. WWDG was collected from two ethanol plants, and protein was extracted by the addition of water, autoclaving to precipitate protein and drying in a forced air oven at 55 °C to create WWDG–protein concentrate (WWDG–PC). This process increased crude protein (CP) and decreased NSP in the WWDG–PC (P < 0.05). Dry matter and energy digestibility of WWDG–PC in rainbow trout were increased by fractionation (P < 0.05). A 56‐day growth trial was performed to determine the effect of feeding WWDG–PC on growth performance of rainbow trout. Rainbow trout (n = 18/tank; body weight = 231 g; 3 tanks/treatment) were fed diets containing 0, 75, 150, 225 or 300 g kg^?1 WWDG–PC. All diets were formulated to contain 386 g kg^?1 digestible CP and 17.6 MJ kg^?1 digestible energy. There was no significant linear or quadratic relationship between inclusion rate and growth, feed intake or feed conversion, indicating that at inclusion levels of up to 300 g kg^?1 of WDDG–PC does not reduce the growth performance of rainbow trout.     

Effects of dietary arginine silicate inositol complex on mineral status in rainbow trout (Oncorhynchus mykiss)

Arginine silicate inositol complex (ASI; arginine 49.47 g kg^?1, silicon 8.2 g kg^?1, inositol 25 g kg^?1), a novel composition that is a bioavailable source of silicon and arginine, has potential benefits for vascular and bone health. We have previously reported that bone mineral content increased and the amount of Ca, P, Mg and Mn in the excreta decreased in poultry with ASI supplementation. In the present study, the effect of ASI supplementation at various levels (0, 500, 1000 mg kg^–1 ASI) on growth, feed intake, feed conversion ratio (FCR) and concentrations of body elements, operculum bone ash and activity of serum alkaline phosphatase (ALP) in rainbow trout was evaluated. Ninety 0+ year‐old rainbow trout with initial average weight of 50 ± 3 g were randomly assigned to three treatment groups, three replicates of 10 fish each. The fish were fed either a basal diet or the basal diet supplemented with either 500 or 1000 mg of ASI. Body weight gain (P = 0.25), feed intake (P = 0.36) and feed efficiency (P = 0.42) were not signifcantly influenced by the dietary ASI supplementation. Per cent operculum bone ash (634 g kg^?1 versus 558 g kg^?1, P = 0.001) and ALP activity (112 UL^–1 versus 92 UL^–1, P = 0.001) linearly increased as dietary ASI supplementation increased. Increasing dietary ASI supplementation linearly increased serum and whole body Ca (P = 0.01), P (P = 0.01), Mg (P = 0.05; P = 0.001) Mn (P = 0.05; P = 0.01) and Zn (P = 0.01; P = 0.02) concentrations respectively. In conclusion, ASI supplementation to the basal diet significantly improved operculum bone ash and whole body mineral content in rainbow trout and did not impact feed consumption, weight gain or FCR.     

Partial replacement of fish oil by soybean oil on lipid distribution and liver histology in European sea bass (Dicentrarchus labrax) and rainbow trout (Oncorhynchus mykiss) juveniles

A 12‐week feeding trial was conducted to evaluate the effects of fish oil replacement by soybean oil, on lipid distribution and liver histology of two commercially important finfish species: rainbow trout (Oncorhynchus mykiss) and European sea bass (Dicentrarchus labrax). Sea bass (16.2 ± 0.5 g; mean ± SD) and rainbow trout (52.1 ± 0.5 g) juveniles were fed one of three isonitrogenous (500 g kg^?1 CP) and isoenergetic (19 kJ g^?1) diets, containing 0% (control, diet A), 25% (diet B) and 50% (diet C) soybean oil. At the end of the experiment, lipid deposition was evaluated in muscle, liver and viscera. Cholesterol and triglycerides levels were also determined in plasma. Tissue total, neutral and polar lipid composition (g kg^?1 total lipids) showed no significant differences within species, regardless the dietary treatment. The same trend was observed for plasma parameters (P > 0.05). Viscera were the preferential tissue of lipid deposition, with 252–276 and 469–513 g kg^?1 total lipid content in trout and sea bass, respectively. Dietary fish oil replacement had no effect on either hepatic lipid droplets accumulation or degree and pattern of vacuolization in the observed liver sections. These data suggest that both sea bass and trout can be fed diets containing up to 50% soybean oil without adverse effects on tissue lipid composition or liver histology.     

Comparative effects of dietary l‐carnitine supplementation on diploid and triploid rainbow trout (Oncorhynchus mykiss)

This study compared the effects of dietary l ‐carnitine and ploidy on growth performances and fatty acid content in rainbow trout (Oncorhynchus mykiss). Fish [initial body weight (BW) = 30 g] reared under high density (50 kg biomass m^?3) were hand‐fed in triplicate (3 tanks treatment^?1, 34 fish tank^?1) twice a day, with three nutritionally identical diets containing 15, 200 or 530 mg l ‐carnitine kg^?1 of diet. No significant growth differences were observed over a 56‐day grow‐out period, during which BWs increased threefold. Growth performances and survival were not significantly affected by either ploidy or dietary l ‐carnitine content, although daily growth index showed an increasing trend (2.52–2.65% day^?1) with increasing dietary l ‐carnitine. Body l ‐carnitine content increased significantly with dietary l ‐carnitine content. Diploid fish had higher plasma ammonia (716–725 μmol L^?1) and osmolality (297–303 mOsm) levels than triploid trout (523–649 μmol L^?1 and 285–291 mOsm, respectively). l ‐carnitine, ploidy and their interaction showed to affect significantly the concentration of several fatty acids. Palmitoleic (16:1), oleic (18:1) and erucic (22:1) acids showed lower concentrations, while the eicosadienoic (20:2n‐6) and arachidonic (20:4n‐6) acids were elevated in liver of triploid fish. Eicosapentaenoic acid (22:5n‐3) was significantly higher in fish fed 200 mg than in fish fed 15 mg l ‐carnitine.     

Effect of ethanolic extract of propolis on growth performance and plasma biochemical parameters of rainbow trout (Oncorhynchus mykiss)

This study was conducted to evaluate the effect of ethanolic extract of propolis (EEP) on growth performance and plasma biochemical parameters of rainbow trout (Oncorhynchus mykiss). Graded levels of EEP [0 (control), 1, 2, and 4 g kg⁻¹ diet] were fed to trout juveniles (mean weight 7.73 ± 0.17 g) for 10 weeks. Dietary EEP supplementation regardless of inclusion level significantly improved the specific growth rate of fish. Similarly, supplemental EEP generally improved the feed efficiency ratio and protein efficiency ratio, but no significant differences were observed between the 1 g kg⁻¹ EEP group and the control group. In addition, dietary EEP supplementation generally increased the plasma superoxide dismutase, lysozyme, total antioxidant capacity, glutathione peroxidase, and catalase activities, but decreased the plasma malondialdehyde level. The plasma triglycerides level was significantly lower in the 1 or 4 g kg⁻¹ EEP group as compared with the control group. Dietary EEP supplementation generally decreased the plasma aspartate aminotransferase and alanine aminotransferase activities, but increased the hepatic aspartate aminotransferase and alanine aminotransferase activities. These results indicate the potential to use the EEP as a growth promoter, hepatoprotective agent, and immunostimulant for rainbow trout.     

Effects of temperature and salinity on oxygen consumption of tawny puffer Takifugu flavidus juvenile

The respiratory rates of Tawny puffer Takifugu flavidus juvenile were measured at four temperatures (20, 23, 26 and 29 °C) and seven salinities (5, 10, 15, 20, 25, 30 and 35 g L^?1). The results showed that both temperature and salinity significantly affected the oxygen consumption of tawny puffer juvenile. The oxygen consumption rate (OCR) increased significantly with an increase in the temperature from 20 to 29 °C. Over the entire experimental temperature range (20–29 °C), the Q₁₀ value was 1.59, and the lowest Q₁₀ value was found between 23 and 26 °C. The optimal temperature for the juvenile lies between 23 °C and 26 °C. The OCR at 25 g L^?1 was the highest among all salinity treatments. The OCRs show a parabolic relationship with salinity (5–35 g L^?1). From the quadratic relationship, the highest OCR was predicted to occur at 23.56 g L^?1. The optimal salinity range for the juvenile is from 23 to 25 g L^?1. The results of this study are useful towards facilitating an increase in the production of the species juvenile culture.     

Biological characteristics of the improved extensive shrimp system in the Mekong delta of Vietnam

Low and unstable shrimp yields of the improved extensive shrimp system has been a tremendous obstacle for economic development in the coastal areas of Southern Vietnam. To investigate the biological characteristics of this system, ponds in the coastal Cai Nuoc district, Mekong delta of Vietnam, were monitored. Results showed that the system was not optimal for shrimp. While chlorophyll a (chl a) (1.51–37.2 μg L^?1), phytoplankton density (6333–974 444 cells L^?1) and zooplankton density (7.1–517.2 ind L^?1) were abundant and comparable to shrimp farms elsewhere, zoobenthic community was very poor (7–1971 ind m^?2). Toxin‐producing cyanobacteria (Oscillatoria limosa, Oscillatoria formosa, Anabaena sp. and Phormidium tenue) were found. Total bacteria and Vibrios were present in large numbers (respectively 1.04 × 10⁵ and 6.64 × 10² CFU mL^?1 in pond water, 6.33 × 10⁵ and 9.47 × 10³ CFU g^?1 in sediment). Presence of toxin‐producing organisms, poor zoobenthic community and abundance of Vibrios all can enhance shrimp susceptibility to diseases. The following measures are recommended to improve the situation: (1) complete testing of seeds for pathogens, (2) not to incorporate fish into shrimp ponds and (3) applying no‐culture breaks and pathogen‐killing chemicals.     

Efficacy of clove oil and ethanol against Saprolegnia sp. and usability as antifungal agents during incubation of rainbow trout Oncorhynchus mykiss (Walbaum) eggs

Inhibitory concentrations of clove oil and ethanol against growth of Saprolegnia sp. hyphae were screened by a modification of the hemp (Cannabis sativa L.) seed MicroPlate (HeMP) method and their usability as antifungal agents during incubation of rainbow trout Oncorhynchus mykiss eggs was tested. In vitro experiment showed that in continuous static exposure, clove oil at 100 mg L^?1 significantly inhibited the growth of Saprolegnia, whereas in bath exposures, clove oil at 500 mg L^?1 had no significant effect at any exposure time tested (15, 60 and 240 min), but clove oil at 10 000 mg L^?1 significantly inhibited growth at all exposure times. Clove oil and ethanol treatments had no visible effects on the onset or spread of the fungus during incubation of rainbow trout eggs. Clove oil at 1000 mg L^?1 resulted in 95–100% mortality before the eyed stage was reached. Sublethal concentrations of clove oil and ethanol had no effects on the development rate of the embryo or growth and yolk utilization efficiency after hatching. This study suggests that clove oil and ethanol may not be options in controlling aquatic fungi infestations during incubation of rainbow trout eggs.     

Dietary yeast culture supplementation improves initial rearing of McConaughy strain rainbow trout

The addition of a yeast culture food supplement (DVAqua from Diamond V. Mills, Cedar Rapids, IA, USA) was evaluated during feeding of McConaughy strain rainbow trout Oncorhynchus mykiss. Two trials were run consecutively, starting with initial feeding, and were replicated over 2 years. The yeast culture was added to commercial trout starter at levels of 0.125 and 0.25 g kg^?1. The number of rainbow trout that died during the first 4 weeks of rearing was significantly reduced in the tanks receiving either of the yeast culture‐supplemented diets compared with the tanks receiving a control starter diet. Ending tank weights and gain were significantly and consistently greater in the tanks fed the 0.25 g kg^?1 yeast culture diet. Individual fish weights were also significantly heavier in the fish‐fed yeast culture containing diets in each year of the study at the end of 27 days. In the trials from 4 to 8 weeks postinitial feeding, mortality rates were significantly less only in the tanks receiving 0.25 g kg^?1 yeast culture supplementation. Individual fish lengths and weights at the end of the second trial were significantly greater in the tanks receiving either level of yeast culture compared with the control diet only in 1 year. Total tank weights and feed conversion were not significantly different between any of the treatments. The inclusion of DVAqua yeast culture provided significant increases in trout survival and growth through the first 4 weeks of feeding, with continued benefits for the next 4 weeks.