Metabolic scope, swimming performance and the effects of hypoxia in the mulloway, Argyrosomus japonicus (Pisces: Sciaenidae)

The culture of the mulloway (Argyrosomus japonicus), like many other Sciaenidae fishes, is rapidly growing. However there is no information on their metabolic physiology. In this study, the effects of various hypoxia levels on the swimming performance and metabolic scope of juvenile mulloway (0.34 ± 0.01 kg, mean ± SE, n = 30) was investigated (water temperature = 22 °C). In normoxic conditions (dissolved oxygen = 6.85 mg l^− 1), mulloway oxygen consumption rate (M·o₂) increased exponentially with swimming speed to a maximum velocity (U_crit) of 1.7 ± < 0.1 body lengths s^− 1 (BL s^− 1) (n = 6). Mulloway standard metabolic rate (SMR) was typical for non-tuna fishes (73 ± 8 mg kg^− 1 h^− 1) and they had a moderate scope for aerobic metabolism (5 times the SMR). Mulloway minimum gross cost of transport (GCOT_min, 0.14 ± 0.01 mg kg^− 1 m^− 1) and optimum swimming velocity (U_opt, 1.3 ± 0.2 BL s^− 1) were comparable to many other body and caudal fin swimming fish species. Energy expenditure was minimum when swimming between 0.3 and 0.5 BL s^− 1. The critical dissolved oxygen level was 1.80 mg l^− 1 for mulloway swimming at 0.9 BL s^− 1. This reveals that mulloway are well adapted to hypoxia, which is probably adaptive from their natural early life history within estuaries. In all levels of hypoxia (75% saturation = 5.23, 50% = 3.64, and 25% = 1 .86 mg l^− 1), M·o₂ increased linearly with swimming speed and active metabolic rate (AMR) was reduced (218 ± 17, 202 ± 14 and 175 ± 10 mg kg^− 1 h^− 1 for 75%, 50% and 25% saturation respectively). However, U_crit was only reduced at 50% and 25% saturation (1.4 ± < 0.1 and 1.4 ± < 0.1 BL s^− 1 respectively). This demonstrates that although the metabolic capacity of mulloway is reduced in mild hypoxia (75% saturation) they are able to compensate to maintain swimming performance. GCOT_min (0.09 ± 0.01 mg kg^− 1 m^− 1) and U_opt (0.8 ± 0.1 BL s^− 1) were significantly reduced at 25% dissolved oxygen saturation. As mulloway metabolic scope was significantly reduced at all hypoxia levels, it suggests that even mild hypoxia may reduce growth productivity.     

Performance of packed column aerator at low hydraulic loading

A laboratory-scale packed column aerator filled with ceramic Raschig rings was tested for its performance with hydraulic loadings in the range of 16–86·3 m³ m⁻² h⁻¹. Two columns of 0·19 m and 0·24 m inside diameter and packing sizes of 15, 25 and 36 mm were used. The system equation developed by previous workers for trickling filters in waste-water treatment was not generally applicable across the lower hydraulic loadings. The system coefficient incorporating the oxygen absorption coefficient (k_La) was found to vary within the range of hydraulic loadings studied. The oxygen transfer rate equation developed for surface and submerged aerators was used for estimating standard oxygen transfer efficiency of the packed column aerator, which, in this case, ranged from 6·2 to 22·6 kg O₂ kWh⁻¹.     

Appetite, gut transit, oxygen uptake and nitrogen excretion in captive Atlantic halibut, Hippoglossus hippoglossus L., and lemon sole, Microstomus kitt (Walbaum)

Atlantic halibut, Hippoglossus hippoglossus L., eat larger satiation meals (mean 11.7% body weight) than lemon sole, Microstomus kitt (Walbaum), (2.6% body weight). Total gut clearance time was about 120 h for halibut and 72 h for lemon sole. There are marked differences in feeding behaviour between the two species; halibut feed in midwater and require several body lengths of approach swimming before taking large items of food, while lemon sole eat only off the bottom. In shared tanks, no aggressive interaction was observed. A duoculture system holding small numbers of lemon sole with the more valuable halibut is recommended as a means of minimizing food waste and tank fouling. Oxygen uptakes of 0.07-0.11 ml O₂ g fish wt⁻¹ h⁻¹ (depending on nutritional state) were recorded for the two species. Ammonia nitrogen outputs were also similar. Starved halibut excreted 2.32 μg N g⁻¹ h⁻¹, fed animals 5.08 μg N g⁻¹ h⁻¹. The corresponding values for lemon sole were 3.26 μg N g⁻¹ h⁻¹ and 6.37 μg N g⁻¹ h⁻¹, respectively.     

Using a macroalgae Ulva pertusa biofilter in a recirculating system for production of juvenile sea cucumber Apostichopus japonicus

A simple indoor recirculating system for production of juvenile sea cucumber (Apostichopus japonicus) was operated on a commercial scale for 90 days during winter. The system consists of three 70 m³ sea cucumber rearing tanks and one biofilter tank where macroalgae (Ulva pertusa) was used as a biofilter in order to reduce water requirements. Effluent from the sea cucumber tanks drained into the macroalgae biofilter tank and were then returned to the sea cucumber tanks by a discontinuous-flow recirculation system. Survival and growth rates in the sea cucumber culture tanks were similar to those in the control tank (with one water exchange per day). The survival rate averaged about 87%. The average body weight increased from 3.5 ± 0.3 g to 8.1 ± 0.8 g and total sea cucumber biomass production over the experimental period was 745 g m⁻² after initial stocking densities of 375 g m⁻². The growth rate of U. pertusa was 3.3% day⁻¹. U. pertusa was efficient in removing toxic ammonia and in maintaining the water quality within acceptable levels for sea cucumber culture; there were only small daily variations of temperature, pH and DO. The U. pertusa tank removed 68% of the TAN (total ammonia-nitrogen) and 26% of the orthophosphate from the sea cucumber culture effluent; the macroalgae biofilter removed ammonia at an average rate of 0.459 g N m⁻² day⁻¹. It would be efficient to use the U. pertusa biofilter in a recirculating system for production of A. japonicus juveniles in winter.     

Filtration of king scallops (Pecten maximus)

Filtration rates of hatchery-reared king scallop (Pecten maximus L.) juveniles, fed a single species alga diet (Pavlova lutheri (Droop) Green), were measured at a range of temperatures (6–21 °C). Weight specific filtration rate (ml min⁻¹ g⁻¹ (live weight)) of juveniles of a selected size range of 17–19 mm shell height (0.26–0.36 g live weight) increased with temperature above 16 °C and decreased below 11 °C, but was not significantly different between these two temperatures. Measurements at 16 °C using juveniles with a wider size range of 10–25 mm shell height (0.05–0.8 g live weight) gave the allometric equation: filtration rate (ml min⁻¹)=12.19×weight (g)^0.887. Filtration rate decreased significantly when the cell concentration was greater than 200 cells μl⁻¹ (4.25 mg (organic weight) l⁻¹). With six other algae food species, filtration rates similar to those with P. lutheri were only achieved with Chaetoceros calcitrans (Paulsen) Takano. All other algae species tested were cleared from suspension at significantly lower rates. Experiments with diet mixtures of P. lutheri and these other algae suggested that this was usually a reflection of lowered filtration activity, rather than pre-ingestive rejection of cells. In experimental outdoor nursery rearing systems, the filtration rate was inversely proportional to the concentration of cells in the inflow, in the range 5–210 cells μl⁻¹. It was not affected by flow rate (2–130 l h⁻¹, equivalent to 0.12–28.38 l h⁻¹ g⁻¹ (live weight)) with scallop juveniles stocked from 2 to 62 g l⁻¹. The results are discussed in relation to on-growing scallops at field sites.     

Physiological changes in rainbow trout held under crowded conditions and fed diets with different levels of vitamins E and C and highly unsaturated fatty acids (HUFA)

Rainbow trout (Oncorhynchus mykiss) maintained in crowded (100 kg m^− 3) and uncrowded (20 kg m^− 3) conditions were fed 42 days with five experimental diets having different levels of vitamin E (25.6 and 275.6 mg kg diet^− 1), C (0 and 1000 mg kg diet^− 1) and HUFA (highly unsaturated fatty acids, 12.5 and 320.5 g kg diet^− 1): −E−HUFA, −E+HUFA, +E−HUFA, +E+HUFA, −C+E+HUFA. Cortisol, plasma metabolites, tissue glycogen, fish composition, and tissue fatty-acid profile were evaluated at the end of the experimental period. In general, no changes in cortisol levels were associated with crowding, although +E+HUFA and −C+E+HUFA fish showed higher levels (mean ± SE, 55.5 ± 11.1 and 78.0 ± 11.3 ng ml^− 1) as a consequence of a possible interaction between chronic crowding and diet composition. Protein and glucose con-centration in plasma displayed no effect of crowding, but liver glycogen showed a general tendency to decrease in −E−HUFA, −E+HUFA, +E−HUFA, +E+HUFA, −C+E+HUFA crowded groups (70.2 ± 2.1, 52.1 ± 2.5, 73.4 ± 7.4, 91.7 ± 3.3, 74.2 ± 8.4 mg g^− 1 tissue, respectively) compared to uncrowded groups (108.9 ± 14.2, 82.7 ± 8.8, 92.4 ± 10.7, 99.1 ± 10.0, 103.5 ± 15.6 mg g^− 1 tissue, respectively), thus proving significant in −E+HUFA fish. Variations in total lipids, triglycerides, total cholesterol and HDL as well as LDL cholesterol in plasma were manifested under crowding conditions, displaying a certain influence of vitamin E and HUFA dietary content. Final body composition, in general, showed no change attributable to fish density, but some differences associated with diet composition were found in lipid and moisture percentages of crowded fish. Liver and muscle fatty-acid profile revealed a clear effect of the dietary lipid source that was more evident in muscle than in liver at normal fish density, and in some cases this effect was modulated by dietary vitamin E and C content and fish-culture conditions.     

Nitrification performance of a propeller-washed bead clarifier supporting a fluidized sand biofilter in a recirculating warmwater fish system

A propeller-wash bead filter (PWBF) and a fluidized sand filter (FSF) on a 28 m³ recirculating system stocked with tilapia maintained favorable water quality at five different feed rates, ranging from 0.9 to 4.5 kg feed per day. TAN removal rates ranged up to about 200 g TAN/m³ of media per day for each of the units. Peak rates of 244 g TAN/m³ of media per day were observed when the recirculating flow was boosted by 20%. Roughly 75% of the removal was accomplished by the fluidized sand filter an observation that is consistent with the difference between the fluidized sand filter volume (0.92 m³) and the bead filter media volume (0.28 m³). The bead filter's primary function was clarification. At the highest daily feed load, over 570 g dry weight of solids were removed during each daily bead filter backwashing event. A 20% increase in flow, at the same daily feed rate, improved solids removal to over 670 g dry weight per bead filter backwash event. The PWBF and FSF combination provided suitable water quality for fish production; however, further increases in feed loading were limited by carbon dioxide buildup and oxygen limitations.     

Production of Florida red tilapia in seawater pools: Nursery rearing with chicken manure and growout with prepared feed

Florida red tilapia (Oreochromis sp.) were reared in 23 m³ seawater (37 ppt) pools. Monosex males (1.3 g mean weight) were stocked at a density of 25 fish/m³ and reared to fingerling size (>10 g) in pools receiving either chicken manure applied at a rate of 105 kg/ha day⁻¹ or pelletized feed (30% protein) administered ad libitum. Following the nursery period, fingerlings in fed pools were reared through adult, marketable sizes.

After 20 days of nursery rearing, mean fish weights (5.7–9.6 g) and survival (77.5–98.6%) in manured pools ranged from less than to greater than values in fed pools (7.9–9.4 g and 95.5–98.2%). By day 33, while mean weights (11.3±0.4 g) and survival (84.5±5.2%) in manured pools were significantly less than those in fed pools (18.0±0.6 g and 95.9±1.4%), fingerling-size fish were obtained from manured pools at an overall productivity of 55 kg/ha day⁻¹.

After 170 days in fed pools, mean fish weight was 467±9 g, survival was 89.7±0.9%, and food conversion was 1.6±0.2. Daily weight gain achieved a maximum of 4.4 g day before a rapid decline in water temperature from 28–29°C to 24–25°C caused a loss of fish appetite and evidence of disease.

The results suggest that while nursery rearing of Florida red tilapia in seawater pools fertilized with chicken manure is feasible, considerable variability in fish performance among pools can be expected, despite identical management methods. In pools receiving prepared feed, high growth rates and survival through adult, marketable sizes suggests a potential for commercial production of Florida red tilapia in seawater.     

Growth efficiency of juvenile barramundi, Lates calcarifer, at high temperatures

Temperature is recognized to be the most important environmental factor affecting growth in fish. Barramundi are cultured over a wide range of temperatures some of which approach the upper thermal tolerance for this species. A growth trial was conducted on juvenile barramundi to examine the effects of high temperatures ranging from the minimum optimal temperature (27 °C) for growth efficiency to the extreme upper thermal limits (39 °C) for feed intake, growth and growth efficiency. Juveniles (4.87 ± 0.32 g) were held at four different temperatures 27, 33, 36 and 39 °C and fed twice daily to satiation (503.5 g kg^− 1 crude protein, 182.5 g kg^− 1 lipid, 150.1 g kg^− 1 ash, 20.52 GE MJ kg^− 1). Feed intake (g·day^− 1) and SGR (%·day^− 1) increased with increasing temperature up to 36 °C. At 39 °C feed intake, growth, feed efficiency ratio, protein efficiency ratio and productive energy value were significantly lower than at the other temperatures. This demonstrates that growth was optimized at temperatures from 27 to 36 °C and that barramundi have a much wider range for maximum growth efficiency than previously thought.     

Marine shrimp aquaculture: a novel waste treatment system

Ecuadorian Penaeus vannamei were cultured in dirt ponds (each of approximately 163 m²) at four different stocking densities, i.e. 5 shrimp m⁻², 10 shrimp m⁻², 15 shrimp m⁻² and 20 shrimp m⁻². Experiments were carried out over three different periods during the year. Each experiment lasted for 11–14 weeks. No commercial feed was given to the shrimp. The only input to the ponds was about 30 kg of cattle manure per pond per week. Chemical composition of the cattle manure was analyzed. Water quality parameters such as temperature, pH, DO and turbidity were recorded twice daily for each experiment; nutrients (nitrite, nitrate, ammonium and phosphate), water ATP, sediment ATP, H₂S and chlorophyll were measured twice weekly for each experiment. Shrimp were sampled either weekly or bi-weekly for body weight measurements.

The results showed a negative correlation between stocking density and growth. Weekly growth ranged from 0·44 to 1·58 g week⁻¹. Survival was over 50% in all treatments and averaged at 70·8%. Under these stocking densities, shrimp production ranged from 4·4 to 18·8 kg ha⁻¹ day⁻¹. The stocking density of 15 shrimps m⁻² provides better production than the other stocking densities.

Water quality data did not relate to any shrimp growth. Water nutrient levels in pond discharge water were less than or equal to the nutrients in the incoming water in spite of the weekly addition of cattle manure and did not increase with the addition of cattle manure. No coliform bacteria were detected in any pond water samples through the study period. This indicates digestion of cattle manure in marine shrimp ponds would not pollute the environment with high concentrations of dissolved nutrients.

Thus, a marine shrimp pond can be considered a dissolved nutrient marine treatment plant converting unwanted cattle manure (1841 kg cattle manure ha⁻¹ week⁻¹ in this study) into a valuable commodity — shrimp.     

Comparing denitrification rates and carbon sources in commercial scale upflow denitrification biological filters in aquaculture

Aerobic biological filtration systems employing nitrifying bacteria to remediate excess ammonia and nitrite concentrations are common components of recirculating aquaculture systems (RAS). However, significant water exchange may still be necessary to reduce nitrate concentrations to acceptable levels unless denitrification systems are included in the RAS design. This study evaluated the design of a full scale denitrification reactor in a commercial culture RAS application. Four carbon sources were evaluated including methanol, acetic acid, molasses and Cerelose™, a hydrolyzed starch, to determine their applicability under commercial culture conditions and to determine if any of these carbon sources encouraged the production of two common “off-flavor” compounds, 2-methyisoborneol (MIB) or geosmin. The denitrification design consisted of a 1.89 m³ covered conical bottom polyethylene tank containing 1.0 m³ media through which water up-flowed at a rate of 10 lpm. A commercial aquaculture system housing 6 metric tonnes of Siberian sturgeon was used to generate nitrate through nitrification in a moving bed biological filter. All four carbon sources were able to effectively reduce nitrate to near zero concentrations from influent concentrations ranging from 11 to 57 mg/l NO₃–N, and the maximum daily denitrification rate was 670–680 g nitrogen removed/m³ media/day, regardless of the carbon source. Although nitrite production was not a problem once the reactors achieved a constant effluent nitrate, ammonia production was a significant problem for units fed molasses and to a less extent Cerelose™. Maximum measured ammonia concentrations in the reactor effluents for methanol, vinegar, Cerelose™ and molasses were 1.62 ± 0.10, 2.83 ± 0.17, 4.55 ± 0.45 and 5.25 ± 1.26 mg/l NH₃–N, respectively. Turbidity production was significantly increased in reactors fed molasses and to a less extent Cerelose™. Concentrations of geosmin and MIB were not significantly increased in any of the denitrification reactors, regardless of carbon source. Because of its very low cost compared to the other sources tested, molasses may be an attractive carbon source for denitrification if issues of ammonia production, turbidity and foaming can be resolved.     

Regional size, age and growth differences of red grouper (Epinephelus morio) along the west coast of Florida

Red grouper (Epinephelus morio) were collected from the west coast of Florida, the central area of fishery harvest in U.S. waters, by fishery-dependent sources during 2000–2005. The west Florida shelf was divided into two regions: north (capture locations ≥28°N latitude) and south (capture locations <28°N latitude). Significant differences were found for age, length, and size-at-age by region and by gear; red grouper from the north were significantly younger and smaller on average than those from the south. Regional differences were also noted with respect to age progression; year class trends were only detected in the north. The 1996 year class dominated the landings in 2000–2001 (ages 4 and 5) and the 1999 year class dominated in 2004–2005 (ages 5 and 6). Regional data were fit to a size-modified von Bertalanffy growth model indicating smaller asymptotic length (L_∞) and faster growth rate (k) in the north (north: L_∞ = 800 mm, k = 0.23 mm year⁻¹, t₀ = 1.12; south: L_∞ = 863 mm, k = 0.15 mm year⁻¹, t₀ = 0.05). Mortality estimates derived from catch curves resulted in higher total and fishing mortality in the north for both gears. Alternative explanations of regional differences likely depend on nursery delineation and correlation to periodic environmental events such as red tides and hurricanes; all possibly important factors based upon anecdotal information. Nevertheless, our finding of regional demographic differences in red grouper from the west coast of Florida suggests a more complex population spatial structure for red grouper.     

Stocking density and shelter type for the optimal growth and survival of western rock lobster Panulirus cygnus (George)

The growth and survival of three size classes of wild caught western rock lobster, Panulirus cygnus (post-pueruli: mean 2.14 ± 0.07 g, 13.2 ± 0.1 mm CL; year 1: post-settlement juveniles, 57.1 ± 1.1 g, 38.7 ± 0.28 mm CL; and year 2 post-settlement juveniles, mean 138.2 ± 2.26 g, 51.9 ± 0.25 mm CL) were examined at combinations of two stocking densities (post-pueruli: 50 and 100 m^− 2; year 1: 11 and 23 m^− 2; year 2: 10 and 19 m^− 2) and two shelter types (a novel rigid plastic mesh shelter or bricks) over a period of 6 months. Survival of lobsters held at the lower densities (90–95%) was significantly greater than for lobsters held at higher densities (post-pueruli = 78%, year 1 = 86%, year 2 = 88%). Post-pueruli survival was significantly higher in tanks with mesh shelters (91.7%) than brick shelters (75.8%) with a similar trend exhibited by year 1 and year 2 lobsters. Densities tested did not significantly affect lobster growth for any size class. Growth of post-pueruli was considerably higher in tanks with mesh shelters (641.7% weight gain; specific growth rate 1.07 BW day^− 1) (p < 0.05) but there was no difference in the growth of year 1 and year 2 lobsters between mesh and brick shelters. Feed intake (g pellet dry matter lobster^− 1 day^− 1) was not significantly different between densities. This study has shown that P. cygnus is well suited for aquaculture based on the collection and ongrowing of wild caught pueruli, as this species exhibits good survival at high densities (up to 100 m^− 2) without adverse effects on growth, and shows no captivity-related health problems. We recommend mesh shelters, with stocking densities of 50 m^− 2 for post-pueruli and between 20 and 25 m^− 2 for year 1 and year 2 juveniles, to maximise survival and production.     

Acoustic analysis of volume variation in a bag-net within a set-net

An experiment designed to measure the volume variation of a bag-net within a set-net was conducted in Jaran Bay, Kosung, Korea. Three radio-acoustic-linked positioning (RAP) buoys, a time controller with a personal computer and seven pingers were used to measure the volumes of the bags. During the April neap tide, the minimum and maximum volumes of the bag-net were 4173 m³ (at 17.00 h) and 4757 m³ (12.00 h), respectively. The average current directions and speeds were 99.9°, 12.9 cm/s and 104.0°, 2.4 cm/s, respectively. During the spring tide, the minimum and maximum volumes of the bag-net were 2016 m³ (18.30 h) and 4454 m³ (15.00 h), respectively. The average current directions and speeds were 315.6°, 16.1 cm/s and 289.0°, 5.7 cm/s, respectively. The minimum (2016 m³) and maximum (5568 m³) volumes of the bag-net were observed during the period when the spring tide changed to the neap tide.     

Modeling industry-wide sediment oxygen demand and estimation of the contribution of sediment to total respiration in commercial channel catfish ponds

Data collected from 45 commercial channel catfish, Ictalurus punctatus, ponds were used to develop empirical models predicting sediment oxygen demand (SOD). Seven acceptable models were combined with a Monte-Carlo sampling distribution to predict industry-wide sediment oxygen demand (SOD_i). The SOD_i values obtained from the best equation were used in simulations to assess the effect of diurnally varying water column dissolved oxygen (DO) concentrations on SOD and the effect of pond water depth on the contribution of SOD to overall pond respiration. Estimated SOD_i ranged from 62 to 962 mg m⁻² h⁻¹, with a mean of 478 mg m⁻² h⁻¹. There was a 95% probability of mean SOD_i being ≥700 mg m⁻² h⁻¹. The effects of diurnal variation in DO concentration in the water column on expression of SOD was modeled by combining maximum SOD_i, an empirical relationship between DO and SOD, and simulated pond DO concentrations. At DO concentrations >15 mg l⁻¹, diel SOD in catfish ponds exceeded 20 g O₂ m⁻² day⁻¹. But when average diel DO was <4 mg l⁻¹ and the range of DO concentration was 6–8 mg l⁻¹, SOD decreased to 13 g O₂ m⁻² day⁻¹ because DO availability limited the full expression of potential SOD. Respiration totals for sediment (average SOD_i), plankton, and fish respiration were calculated for pond water depths ranging from 0.25 to 4 m. Although whole-pond respiration increases as pond depth increases, the proportion of total respiration represented by sediment decreased from 48 to 10% by increasing water depth over this range. The results of these studies show that SOD is a major component of total pond respiration and that certain management practices can affect the impact of SOD on pond oxygen budgets. Mixing ponds during daylight hours, either mechanically or by orienting ponds for maximum wind fetch, will increase oxygen supply to sediments, thereby allowing maximum expression of SOD and maximum mineralization of sediment organic matter. Given a mixed condition caused by wind or other artificial means, the construction of deeper ponds increases the total mass of DO available for all respiration, causing nighttime DO concentrations to decline at a slower rate, reducing the need for supplemental aeration. Because a pond’s water volume decreases over time from sediment accumulation, annual aeration costs will increase with pond age. Constructing ponds with greater initial depth will therefore reduce long-term cost of aeration, allow more flexible management of pond water budget, and reduce the long-term expense associated with pond reconstruction.     

Energy and nitrogen partitioning in 250 g Atlantic cod (Gadus morhua L.) given graded levels of feed with different protein and lipid content

The effects of feed intake level on energy and nitrogen partitioning were studied in juvenile Atlantic cod (250 g) fed two fish meal based diets differing in protein and lipid content (54:31 and 65:16) at 10 °C. Replicate groups of cod were feed deprived for 32 days or fed one of the two diets at 25, 50, 75 or 100% of group satiation for 60 days. Feed intake and oxygen consumption were measured daily and weights and chemical composition of carcass, liver, viscera and whole body were measured at start and end. Diet digestibilities were assessed in a separate experiment.

The whole body and carcass growth rates at a given feed intake did not differ between dietary groups, but the liver grew faster in the fish fed the low protein diet, resulting in higher hepatosomatic indices at the end of the experiment in the groups fed this diet.

The efficiency of utilisation of digestible nitrogen for growth (k_DNg) was higher for the low protein diet (0.73 ± 0.02) than for the high protein diet (0.53 ± 0.05), resulting in higher nitrogen retention at a given nitrogen intake. No difference in percentage nitrogen retention was seen in full-fed fish however (31.2 ± 2.5 and 28.4 ± 1.6% for the low protein and high protein diets, respectively). This can be explained by higher nitrogen intake in the fish fed the high protein diet, resulting in a smaller proportion of the intake being used for maintenance.

There was no difference in energy utilisation between dietary groups. The digestible energy requirement for maintenance (DE_maint) was 53.8 ± 0.9 kJ kg^− 1 d^− 1 (42.3 ± 0.7 kJ kg^− 0.8 d^− 1) and the utilisation efficiency for growth (k_DEg) was 0.80 ± 0.02. The energy retention in full-fed fish was 31.3 ± 3.5 and 31.7 ± 1.0% for the low protein and high protein diets, respectively. The deposited energy was distributed in approximately equal proportions in the liver and carcass, whereas viscera accounted for a minor proportion. At a given energy intake, the fish fed the high protein diet deposited more energy in the carcass and less in the liver than did those fed the low protein diet.     

Effect of water temperature on the immune response of white shrimp Litopenaeus vannamei to Vibrio alginolyticus

White shrimp Litopenaeus vannamei held in 25‰ seawater at 27 °C or 28 °C were injected with TSB-grown Vibrio alginolyticus at 1 × 10⁴ colony-forming units (cfu) shrimp^− 1 or 1 × 10⁵ cfu shrimp^− 1, and then cultivated onward at water temperatures varying from 20 to 34 °C. Over 24–144 h, mortality of V. alginolyticus-injected shrimp held at 34 °C or 32 °C was significantly higher than that of shrimp held at lower temperatures. In a separate experiment, shrimp held in 25‰ seawater at 28 °C and then cultured onward at 20 to 32 °C were examined for immune parameters at 24–96 h. THC, phenoloxidase activity, respiratory burst, and SOD activity decreased significantly at 24 h after transfer to 32 °C. Shrimp held in 25‰ seawater at 27 °C and then cultured onward at 20 to 34 °C showed a significant reduction in phagocytic activity and clearance efficiency for V. alginolyticus at 24 h after transfer to 34 °C. It was concluded that transfer of shrimp from 27 or 28 °C to higher temperatures (32 and 34 °C) reduced their immune capability and decreased resistance to V. alginolyticus infection.     

Serotonin induces ovarian maturation in giant freshwater prawn broodstock, Macrobrachium rosenbergii de Man

This study investigated the effects of serotonin (5-hydroxytryptamine or 5HT) on ovarian development in Macrobrachium rosenbergii de Man. Adult female prawns at the ovarian stage I (spent) were injected with 5HT at 1, 5, 10, 20 and 50 μg g^− 1 body weight (BW) intramuscularly on days 0, 5 and 10, and sacrificed on day 15. The doses as related to the effect could be categorized into three levels: low (1 and 5 μg g^− 1 BW of 5HT), medium (10 and 20 μg g^− 1 BW of 5HT) and high (50 μg g^− 1 BW of 5HT). The low-dose, especially at 1 μg g^− 1 BW, caused prawns to exhibit a significant increase in ovarian index (ovarian weight/body weight × 100) (5.79 ± 0.09%) as compared to the control (1.49%). The ovaries of most of these prawns could develop to stage IV (mature) and contained synchronously mature oocytes while most of the control ovaries remained at stage I and II (proliferative), and contained only oogonia to previtellogenic (Oc1, Oc2) and early vitellogenic oocytes (Oc3). The medium- and high-dose treated prawns exhibited ovaries that could reach stages III and IV and contained various types of oocytes of different maturity. Pretreatment with 5HT receptor antagonist, cyproheptadine (CYP), at 10 μg g^− 1 BW before 5HT injection significantly suppressed the effect of 5HT. Intramuscular injection of the 5HT-primed thoracic ganglion culture medium into CYP-pretreated prawns resulted in the increase of ovarian index about 5–6 times more than in the control, and in the groups injected with 5HT-primed media from muscle strip, eyestalk and brain. The ovaries of most prawn could develop up to stage IV and contained synchronously developed vitellogenic (Oc4) and mature oocytes (Oc5). These findings suggest that 5HT indirectly induces ovarian development and oocytes maturation in M. rosenbergii, probably via a putative ovarian stimulating factor released from the thoracic ganglia.     

The effect of dietary protein replacement by crystalline amino acid on growth and nitrogen utilization of turbot Scophthalmus maximus juveniles

A study was conducted to evaluate the effect of partial replacement of dietary fish meal by crystalline amino acids on growth performance, feed utilization, body composition and nitrogen utilization of turbot juveniles.

Four diets were formulated to be isolipidic (12% DM) and isonitrogenous (8% DM). A fish meal based diet was used as control. In the experimental diets, a crystalline amino acid (AA) mixture was used to partially replace fish meal, corresponding to a non-protein nitrogen content of 19, 37 and 56%, respectively (diets 19AA, 37AA and 56AA, respectively). The overall amino acid profile of the experimental diets resembled that of the whole-body protein of turbot. Each experimental diet was fed to triplicate groups of 20 fish (initial body weight of 31.8 g) twice daily to apparent satiation for 42 days. During the trial water temperature averaged 18 °C.

Final body weight, weight gain (g kg ABW^− 1 day^− 1) and specific growth rate were not different between the control and 19AA diet but significantly decreased with the increase of crystalline-AA inclusion from 19 to 56%. Feed intake and feed efficiency of fish fed the control and diet 19AA were similar and significantly higher than those of fish fed the 56AA diet. At the end of the growth trial, there were no significant differences in whole-body composition among groups. Hepatosomatic index was also unaffected by dietary treatments.

Nitrogen retention (g kg ABW^− 1 day^− 1) of fish fed the control and the 19AA diets were similar and significantly higher than that of fish fed the other diets. Expressed as a percentage of the nitrogen intake, N retention was significantly higher with the control than with the 37AA and 56AA diets.

Daily ammonia excretion (mg kg ABW^− 1 day^− 1) of fish fed the control diet was significantly higher than that of fish fed the 37AA and 56AA diets, while daily urea excretion (mg kg ABW^− 1 day^− 1) did not significantly differ among treatments. Non-fecal nitrogen (ammonia + urea) excretion (mg kg ABW^− 1 day^− 1) was significantly higher for fish fed the control diet than in those fed the 37AA and 56AA diets. However, as percent of N intake, ammonia excretion and non-fecal N excretion were significantly higher in fish fed the 56AA diet than in those fed the control and 19AA diets.

Specific activity of glutamate dehydrogenase, alanine and aspartate aminotransferases did not significantly differ among experimental groups.

In conclusion, in diets with an overall amino acid profile resembling that of the whole-body protein of turbot, crystalline-AA may replace 19% of dietary protein without negatively affecting growth performances or feed utilization efficiency. However, higher protein replacement levels of protein-bound-AA by crystalline-AA severely depressed growth performance.     

Efficacy of bithionol as an oral treatment for amoebic gill disease in Atlantic salmon Salmo salar (L.)

This study examined the efficacy of bithionol as an oral treatment for Atlantic salmon Salmo salar affected by amoebic gill disease (AGD). The current commercial management strategy of AGD is a costly 3 h freshwater bath. It is labour intensive and the number of baths needed appears to be increasing; hence, there is an effort to identify alternative treatments. Efficacy was examined by feeding AGD-affected Atlantic salmon twice daily to satiation with bithionol, an antiprotozoal, at 25 mg kg^− 1 feed. Three seawater (35‰, 17 °C) re-circulation systems were used each consisting of three tanks containing 32 Atlantic salmon smolts with an average (± SEM) mass of 90.4 g (± 5.2). Three feeds were examined in the trial including bithionol, plain commercial control and oil coated commercial control. Feeding commenced 2 weeks prior to exposure to Neoparamoeba spp. at 300 cells L^− 1 and continued for 28 days post-exposure. Efficacy was determined by examining gross gill score and identifying percent lesioned gill filaments twice weekly for 4 weeks post-exposure. Bithionol when fed as a two-week prophylactic treatment at 25 mg kg^− 1 feed delayed the onset of AGD pathology and reduced the percent lesioned gill filaments by 53% and halved the gill score from 2 to 1 when compared with both the plain and oil controls during an experimental challenge. There were no palatability problems observed with mean feed intake of bithionol over the trial duration with fish consuming higher levels of the bithionol diet compared to both the oil and plain controls. This study demonstrated that bithionol at 25 mg kg^− 1 feed, when fed as a two-week prophylactic treatment for Neoparamoeba spp. exposure, delayed and reduced the intensity of AGD pathology and warrants further investigation as an alternative to the current freshwater bath treatment for AGD-affected Atlantic salmon.