Temperature‐dependent feed requirements in farmed blue mussels (Mytilus edulis L.) estimated from soft tissue growth and oxygen consumption and ammonia‐N excretion

Feed requirements were estimated from specific growth rates in standardized soft tissue dry weight (SGR_DW’) and atomic O:N ratios for mussels fed seven rations of microalgae (5–735 μg C h^?1 ind^?1) at 7 and 14°C respectively. The mean oxygen consumption and ammonia‐N excretion rates were significantly higher at 14°C (0.29 μg O² and 27.3 μg N ind^?1 h¹) compared with those at 7°C (0.16 μg O² and 11.4 μg N ind^?1 h^?1) (P < 0.05), resulting in O:N ratios between 3 and 45 at 7°C and 7 and 28 at 14°C. Low O:N ratios indicate protein catabolism and an unfavourable condition, whereas high ratios indicate that carbohydrate is the primary energy source. The measured SGR_DW’ suggests minimum feed requirements of ~240 and ~570 μg C ind^?1 h^?1 for weight maintenance at 7 and 14°C, with corresponding O:N ratios of 24 and 16, respectively, indicating a more stressed condition at 14°C. A 0.5% SGR_DW’ day^?1 was obtained by ~565 (O:N = 29) and ~680 (O:N = 23) μg C ind^?1 h^?1 at 7 and 14°C respectively. A positive and significantly higher SGR_DW’, with the lowest feed ration at 7°C compared with a negative SGR_DW’ at 14°C (P < 0.05), indicated that storage time can also possibly be prolonged at low temperatures if the mussels are not fed.     

Effectiveness of eugenol sedation to reduce the metabolic rates of cool and warm water fish at high loading densities

Effects of eugenol (AQUI‐S^®20E, 10% active eugenol) sedation on cool water, yellow perch Perca flavescens (Mitchill), and warm water, Nile tilapia Oreochromis niloticus L. fish metabolic rates were assessed. Both species were exposed to 0, 10, 20 and 30 mg L^?1 eugenol using static respirometry. In 17°C water and loading densities of 60, 120 and 240 g L^?1, yellow perch controls (0 mg L^?1 eugenol) had metabolic rates of 329.6–400.0 mg O₂ kg^?1 h^?1, while yellow perch exposed to 20 and 30 mg L^?1 eugenol had significantly reduced metabolic rates of 258.4–325.6 and 189.1–271.0 mg O₂ kg^?1 h^?1 respectively. Nile tilapia exposed to 30 mg L^?1 eugenol had a significantly reduced metabolic rate (424.5 ± 42.3 mg O₂ kg^?1 h^?1) relative to the 0 mg L^?1 eugenol control (546.6 ± 53.5 mg O₂ kg^?1 h^?1) at a loading density of 120 g L^?1 in 22°C water. No significant differences in metabolic rates for Nile tilapia were found at 240 or 360 g L^?1 loading densities when exposed to eugenol. Results suggest that eugenol sedation may benefit yellow perch welfare at high densities (e.g. live transport) due to a reduction in metabolic rates, while further research is needed to assess the benefits of eugenol sedation on Nile tilapia at high loading densities.     

Effect of temperature and phytoplankton concentration of Partitioned Aquaculture System water on freshwater mussel filtration

The freshwater mussel Elliptio complanata was provided green algal‐dominated water from a Partitioned Aquaculture System (PAS) over a range of water temperatures (6.1–32.4 °C) and suspended particulate organic carbon (POC) concentrations (<1–32.2 mg C L^?1) to determine filtration rates as mg POC kg^?1 wet tissue weight h^?1. The lowest filtration rates were observed at lowest temperatures and POC concentrations while the highest rates were at intermediate temperatures and the highest POC levels. The predicted filtration rate (PFR) in response to water temperature and POC concentrations was as follows: ln PFR=1.4352+0.1192 POC+0.1399 T?0.0001 T³. Within the experimental conditions, PFRs at any POC concentration increased with increased water temperature to a peak at 22 °C and then decreased. The maximum PFR occurred at 22 °C and 32 mg C L^?1 and the minimum PFR at 7 °C and 1 mg C L^?1. A model to describe the mussel filtration rate responses to PAS water conditions involves both water temperature and POC concentration.     

Comparison of the physiological energetics between Mytilus chilensis,Mytilus galloprovincialis and their hybrids,under laboratory conditions

Laboratory‐produced juvenile individuals of the species Mytilus chilensis, M. galloprovincialis and their hybrids were subjected to physiological measurements under an experimental diet of Isochrysis galbana (30 × 10⁶ cells L^?1), 13°C temperature and a salinity of 30 psu. Pure species individuals showed a higher clearance rate (CR). Mytilus chilensis had a CR of 1.13 L h^?1, while M. galloprovincialis registered only 0.78 L h^?1. Also, pure taxa registered higher values (above 70%) of absorption efficiency when compared with hybrid individuals. Ammonia excretion in M. chilensis and M. galloprovincialis was 1.5% and 0.4%, respectively, while hybrids registered significantly lower values. Under these experimental conditions, M. chilensis registered the highest scope for growth (P < 0.05), compared with M. galloprovincialis and their hybrids. However, the net growth efficiency index (K ₂) in hybridization type I (♀Mg × ♂Mc) was higher (P < 0.05) than other experimental groups. The invasive mytilid M. galloprovincialis showed values that are very similar to those obtained with the hybridization I group (♀Mg × ♂Mc). Finally, we discuss that water temperature is an important factor in the biogeographic separation of both species and the potential effects that the settlement of the invasive species may have for Chilean mussel production.     

Effects of temperature on food consumption, growth and oxygen consumption of freshwater prawn Macrobrachium rosenbergii (de Man 1879) postlarvae

Effects of temperature on food consumption, growth and oxygen consumption were estimated for the freshwater prawn Macrobrachium rosenbergii postlarvae at 23 °C, 28 °C and 33 °C in the laboratory. The results showed that the animal's initial body weight had a close linear relationship with food consumption and growth. Food consumption increased directly with temperature. Consumption rates (C; mg day^?1 ind^?1 ) of the 28 °C and 33 °C groups were much higher than that of the 23 °C group (P < 0.001), and the 33 °C group's consumption rate was higher than that of the 28 °C group (P < 0.05). The relationship of food consumption with temperature and initial body weight (W; mg) could be described as: C = 0.0679W + 0.185t? 3.17. Growth increased significantly with increased temperature. The relationship among specific growth rate, temperature and initial body weight was as follows: SGR = ?0.110W + 0.213t + 0.176. However, temperature showed no effect on growth efficiency. Oxygen consumption increased significantly with temperature (P < 0.01). The weight‐specific oxygen consumption rates (mg O₂ g^?1 h^?1) at 23 °C, 28 °C and 33 °C were 0.83, 1.16 and 1.49 mg O₂ g^?1 h^?1 for 61.92 mg M. rosenbergii.     

Survival, growth and biochemical parameters of silver catfish, Rhamdia quelen (Quoy & Gaimard, 1824), juveniles exposed to different dissolved oxygen levels

Silver catfish, Rhamdia quelen (Quoy & Gaimard, 1824), is an endemic species from Latin America that is raised in cultivation ponds, and consequently may be exposed to low oxygen levels. Therefore, the objective of this study was to verify the lethal concentration (CL_{50?96 h}) of dissolved oxygen levels for silver catfish juveniles. In addition, the effects of different dissolved oxygen levels (1.96±0.08, 3.10±0.10, 4.14±0.09, 5.20±0.07 and 6.16±0.03 mg L^?1) on growth and metabolic parameters (glycogen, glucose, protein, lactate levels and catalase activity) were also investigated. CL_{50?96 h} was 0.52 mg L^?1 (CI 0.42–0.61 mg L^?1) or 6.7% oxygen saturation. After exposure of silver catfish to hypoxia for 30 days, there were no changes in biochemical parameters indicating the use of an anaerobic pathway by the fish. However, the dissolved oxygen levels influenced silver catfish juvenile behaviour, survival and growth, and under the experimental conditions 5.2 mg L^?1 (or 65.6% oxygen saturation) is the minimum oxygen level recommended for the growth of this species.     

Preliminary success using hydrogen peroxide to treat Atlantic salmon,Salmo salar L., affected with experimentally induced amoebic gill disease (AGD)

Currently, the only effective and commercially used treatment for amoebic gill disease (AGD) in farmed Tasmanian Atlantic salmon is freshwater bathing. Hydrogen peroxide (H₂O₂), commonly used throughout the aquaculture industry for a range of topical skin and gill infections, was trialled in vitro and in vivo to ascertain its potential as an alternative treatment against AGD. Under in vitro conditions, trophozoites of Neoparamoeba perurans were exposed to three concentrations of H₂O₂ in sea water (500, 1000 and 1500 mg L^?1) over four durations (10, 20, 30 and 60 min) each at two temperatures (12 and 18 °C). Trophozoite viability was assessed immediately post‐exposure and after 24 h. A concentration/duration combination of 1000 mg L^?1 for >10 min demonstrated potent amoebicidal activity. Subsequently, Atlantic salmon mildly affected with experimentally induced AGD were treated with H₂O₂ at 12 and 18 °C for 15 min at 1250 mg L^?1 and their re‐infection rate was compared to freshwater‐treated fish over 21 days. Significant differences in the percentage of filaments affected with hyperplastic lesions (in association with amoebae) and plasma osmolality were noted between treatment groups immediately post‐bath. However, the results were largely equivocal in terms of disease resolution over a 3‐week period following treatment. These data suggest that H₂O₂ treatment in sea water successfully ameliorated a clinically light case of AGD under laboratory conditions.     

Recirculation nursery systems for bivalves

In order to increase production of bivalves in hatcheries and nurseries, the development of new technology and its integration into commercial bivalve hatcheries is important. Recirculation aquaculture systems (RASs) have several advantages: high densities of the species can be cultured resulting in a cost-effective production system; optimal temperature maximizes production and allows rapid turnover of the product; stable water quality improves growth rate and minimizes stress and potential loss by diseases. Pilot RAS systems were developed for seed rearing of oysters (Crassostrea gigas), scallops (Pecten maximus), mussels (Mytilus edulis) and clams (Ruditapes decussatus). Optimal feed addition and waste matrix were determined. Based on this, system flow rates were designed. Seed growth in the pilot RAS systems was compared at different renewal rates and with growth in flow-through systems (FTS). All four species can be reared in RAS and showed similar growth in RAS and in FTS or in RAS with a higher renewal rate. RAS can keep O₂, nitrogen and pH within the desired range. Temperature was generally higher in RAS than in FTS, probably due to heat induced by the pump circulating the water. The supply of sufficient amount of food in combination with a desire to reduce the renewal rate calls for use of concentrated feed in RAS.     

Effects of salinity on standard metabolic rate of juvenile marbled spinefoot (Siganus rivulatus)

Marbled spinefoot, Siganus rivulatus, is a herbivorous euryhaline teleost widely distributed in the Eastern Mediterranean. It is an economically valuable species and a suitable candidate for warm water aquaculture. Accordingly, understanding the effects of environmental factors on fish metabolism is important to optimize culture conditions. Two experiments were performed to establish standard metabolic rate and study the effect of salinity on metabolism of marbled spinefoot. In the first experiment, a series of flow‐through respirometry experiments was performed at 27°C and 35 g L^?1. The standard metabolic rate of marbled spinefoot juveniles was calculated as 0.57 ± 0.02 mg O₂ g^?1 h^?1 (mean ± SE). In the second experiment, fish were maintained at salinities of 25, 30, 35 and 40 g L^?1 for 2 weeks. Flow‐through respirometry was performed to measure respiration rates at the various salinities. Respiration rates were similar among fish in salinities of 30, 35 and 40 g L^?1 but increased significantly at 25 g L^?1. Results suggest that despite the euryhalinity of marbled spinefoot, farmers should maintain salinity within the optimal range of 30–40 g L^?1 in order to improve productivity.     

Haematological and biochemical profiles of carp blood following nitrite exposure at different concentrations of chloride

Haematological parameters of 2‐year‐old carp (Cyprinus carpio L.) were assessed to study the protective effect of chloride on the health of fish exposed to elevated nitrite concentrations. Four groups of carp were exposed to different concentrations of nitrite and chloride for 96 h (group E1: 67 mg L^?1 NO₂^?, 11 mg L^?1 Cl^?; group E2: 67 mg L^?1 NO₂^?, 100 mg L^?1 Cl^?; group E3: 0 mg L^?1 O₂^?, 100 mg L^?1 Cl^? and group C: 0 mg L^?1 NO₂^?, 11 mg L^?1 Cl^?). The main haematological response of carp to an acute exposure to nitrite (group E1) was a significant decrease (P<0.05) in haemoglobin concentrations (53.40±6.61 g L^?1), haematocrit (0.21±0.02 LL^?1), erythrocyte count (1.13±0.12 TL^?1), leucocyte count (7.1±4.19 GL^?1) and lymphocyte count (5.28±2.51 GL^?1), and a significant increase in methaemoglobin concentration (90.50±4.38%, P<0.01) and mean corpuscular haemoglobin concentration (0.27±0.2 LL^?1, P<0.05). At higher chloride concentrations (group E2), a lower nitrite toxicity was observed. In group E2 carp, methaemoglobin made up 38.32±13.30%. Erythrocytes in carp exposed to nitrite showed qualitative changes. Compared with the control group C, group E1 carp showed a significantly higher number (P<0.05) of elongated erythrocytes, with the nucleus located at one cell pole (0.519±0.388 TL^?1). All erythrocytes of group E1 carp had remarkably clear cytoplasms compared with the cytoplasm in the control group C. The biochemical values found were comparable with those found in controls. The main histological lesions were found in the gills of carp exposed to nitrite and consisted of hyperplasia and an elevated number of chloride cells.     

Water quality,Vibrio density and growth of Pacific white shrimp Litopenaeus vannamei (Boone) in an integrated biofloc system with red seaweed Gracilaria birdiae (Greville)

An indoor trial was conducted for 42 days to evaluate water quality, Vibrio density and growth of Litopenaeus vannamei in an integrated biofloc system (IBS) with Gracilaria birdiae. Four treatments were used, each in triplicate: Control (monoculture shrimp); IBS 2.5 (L. vannamei and 2.5 kg wet weight seaweed m^?3); IBS 5.0 (L. vannamei and 5.0 kg wet weight seaweed m^?3) and IBS 7.5 (L. vannamei and 7.5 wet weight seaweed m^?3). Shrimp individuals (0.34 ± 0.01 g) were stocked at a density of 500 shrimp m^?3. No water exchange was carried out during the experimental period. Molasses was added once a day as an organic carbon source to maintain the C:N ratio at 12:1. The IBS significantly decreased (P < 0.05) dissolved inorganic nitrogen (DIN) ranging from 19% to 34% (3.12–3.83 mg L^?1), NO₃‐N ranging from 19% to 38% (2.40–3.16 mg L^?1), Vibrio density ranging from by 8–83% (0.40–2.20 log 10³ colony‐forming units mL^?1), and FCR ranging from by 20–30% (1.20–1.37), as compared to the control (4.73 mg L^?1, 3.93 mg L^?1, 2.40 log 10³ colony‐forming units mL^?1, and 1.74 respectively). Moreover, the IBS significantly increased (P < 0.05) crude protein in whole body shrimp, ranging from 8% to 13% (13.2–13.7% wet weight basis); as well as final weight, ranging from 25% to 32% (3.90–4.12 g), weekly growth ranging from 25% to 34% (0.59–0.63 g), and shrimp yield by 22–39% (1.72–1.96 kg m^?3), as compared to control (12.1% wet weight basis, 3.12 g, 0.47 g, and 1.41 kg m^?3 respectively). It can thus be concluded that cultivating Gracilaria birdiae in an IBS with L. vannamei can contribute to DIN and NO₃‐N removal, lower Vibrio density, increased crude protein in whole body shrimp, higher growth and yield parameters in shrimp culture.     

Nursery performance of Pacific white shrimp (Litopenaeus vannamei Boone, 1931) cultivated in a biofloc system: the effect of adding different carbon sources

Effect of different carbon sources on nursery performance of Pacific white shrimp (Litopenaeus vannamei) cultivated in biofloc system was investigated. Shrimp postlarvae (98.47 ± 8.6 mg) were fed for 32 days in tanks with water volume of 130 L and density of 1 individual L^?1. One control treatment and four biofloc treatments (BFT1, BFT2, BFT3 and BFT4) with adding different carbon sources including molasses, starch, wheat flour and mixture of them, respectively, were considered at equal weight ratios. According to the results, salinity, dissolved oxygen and pH were not significantly different among the biofloc treatments (P > 0.05). Maximum pH (8.27) and maximum dissolved oxygen (6.35 mg L^?1) were recorded in the control. Maximum (0.43 mg L^?1) and minimum (0.09 mg L^?1) ammonia were recorded in the control and BFT2, respectively (P < 0.05). Using simple carbohydrates (molasses and starch) lowered the ammonia concentration significantly. The highest increase in body weight (1640.43 ± 231.28 mg), growth rate, specific growth rate (8.97 ± 0.42% per day) and biomass (190.29 ± 26.83 mg) were found in BFT1 and the highest survival (90 ± 0.77%) was found in BFT4. The highest feed conversion (1.52 ± 0.23) and the lowest feed efficiency (66.81 ± 7.95) were observed in the control (P < 0.05). The proximate composition analysis revealed an increase in lipid and ash in biofloc treatments. Results indicated that using biofloc technology with zero‐water exchange system and adding carbon sources could help to recycle waste and improve the water quality. Moreover, the type of carbonaceous organic matter as a substrate for heterotrophic bacteria would be effective in degradation and metabolization of ammonia and nitrite.     

Nitrogenous and phosphorus excretions in juvenile silver catfish (Rhamdia quelen) exposed to different water hardness, humic acid, and pH levels

This study examined ammonia, urea, creatinine, protein, nitrite, nitrate, and phosphorus (P) excretion at different water hardness, humic acid, or pH levels in silver catfish (Rhamdia quelen) juveniles. The fish were exposed to different levels of water hardness (4, 24, 50, or 100 mg L^?1 CaCO₃), humic acid (0, 2.5, or 5.0 mg L^?1), or pH (5.0, 6.0, 7.0, 8.0, or 9.0) for 10 days. The overall measured nitrogen excretions were 88.1 % (244–423 μmol kg^?1 h^?1) for ammonia, 10.9 % (30–52 μmol kg^?1 h^?1) for creatinine, 0.02 % (0.05–0.08 μmol kg^?1 h^?1) for protein, 0.001 % (0.002–0.004 μmol kg^?1 h^?1) for urea, 0.5 % (0.64–3.6 μmol kg^?1 h^?1) for nitrite, and 0.5 % (0.0–6.9 μmol kg^?1 h^?1) for nitrate, and these proportions were not affected by water hardness or humic acid levels. The overall P excretion in R. quelen was 0.14–2.97 μmol kg^?1 h^?1. Ammonia excretion in R. quelen usually was significantly higher in the first 12 h after feeding, and no clear effect of water hardness, humic acid levels, and pH on this daily pattern of ammonia excretion could be observed. Water hardness only affected the ammonia and P excretion of R. quelen juveniles in the initial and fifth days after transfer, respectively. The exposure of this species to humic acid increased ammonia excretion after 10 days of exposure but did not affect P excretion. An increase in pH decreased ammonia and increased creatinine excretion but did not change P excretion in R. quelen. Therefore, when there is any change on humic acid levels or pH in the culture of this species, nitrogenous compounds must be monitored because their excretion rates are variable. On the other hand, P excretion rates determined in the present study are applicable to a wide range of fish culture conditions.     

Interactions of different sodium and potassium concentrations on Macrobrachium rosenbergii (de Man) offspring quality parameters

The present study evaluated various sodium and potassium concentrations in hatchery water to determine which proportions would be optimal for Macrobrachium rosenbergii larviculture. Using a closed RAS system (60‐L), experiments were conducted in two stages. In the first stage, larval quality parameters were compared among triplicate treatments of sodium (2000, 3000, 4000 and 5000 mg L^?1) and potassium (100, 150, 200 and 250 mg L^?1). During the second stage, these same parameters were compared from interactions of the two best concentrations determined in the first stage. Initial larval density was fixed at 100 larvae L^?1 and larval quality parameters such as larval stage index (LSI), larval condition index (LCI), larvae dry weight, survival (%), LC₅₀‐24 h for formalin stress and time of the first postlarvae (PL) appearance were measured. Results showed that during the early larval period time LSI, LCI and survival parameters were affected only by potassium and the interaction with sodium was not significant. At a later period of the larval development, interactions between both sodium and potassium were measurable for LSI (P < 0.05) while the interactions on LCI and survival were not significant. Measurable differences among the combined treatments 4000 mg L^?1 sodium and 150 mg L^?1 potassium resulted in the best performance for M. rosenbergii larviculture. This concentration also provided the highest final survival to PL metamorphosis (40.6 ± 2.5%) which was at least 10% higher than the other treatments.     

Sex differences in metabolic rate and swimming performance in pink salmon (Oncorhynchus gorbuscha): the effect of male secondary sexual traits

Do secondary sexual traits, such as large dorsal hump and hooked snout, decrease the swimming efficiency of male pink salmon during freshwater migration? This is the first study to address the effects of secondary sexual traits in pink salmon on oxygen uptake and swimming capacity. We conducted a laboratory experiment using a swimming respirometer and a field study using electromyogram (EMG) telemetry in the Shibetsu River, Hokkaido, Japan. We compared the relationship between MO₂ (mg O₂·kg^?1·h^?1) and swimming velocity U (m·s^?1) in male and female fish, and also investigated the effects of morphological traits (secondary sexual characters) on the relationship between MO₂ (mg O₂·kg^?1·h^?1) and swimming velocity U (m·s^?1). Additionally, we compared energy costs and swimming behaviour during upstream migration between male and female pink salmon. The laboratory experiment revealed that MO₂ exponentially increased with increasing U; this increase was described by MO₂ = 167.9e^1.23U for males and 144.9e^1.14U for females. Linear mixed models found that hump height and the upper jaw length in males significantly and positively affected the relationship between MO₂ and U; no effect was found in females. The field study found that swimming velocity for both sexes estimated from EMG calibration was lower than optimal swimming velocity (U_opt) calculated from the laboratory experiment. We suggest that pink salmon in the Shibetsu River do not swim at the optimal swimming velocity because of the short migration distance involved (20 km).     

Effect of temperature and phytoplankton concentration on Nile tilapia Oreochromis niloticus (L.) filtration rate

Nile tilapia Oreochromis niloticus (L.) held in timed‐pulse feeding chambers, were provided with algal‐rich water dominated by either green algae (Scenedesmus, Ankistrodesmus, Chlorella and Tetraedron) or cyanobacteria (Microcystis) to determine the effect of temperature and phytoplankton concentration on filtration rates. Green algae and cyanobacteria filtration rates were measured as suspended particulate organic carbon (POC) kg^?1 wet fish weight h^?1. Ivlev's filter‐feeding model described the relationships between filtration rates and suspended POC concentration of green algae and cyanobacteria. Filtration rates of both green algae and cyanobacteria increased linearly as water temperature increased from 17 °C to 32 °C and were significantly higher in the warm‐water regime (26–32 °C) than in the cool‐water regime (17–23 °C). Filtration rates at 95% saturation POC (FR₉₅) in green algal and cyanobacterial waters were 700 mg C kg^?1 h^?1 and 851 mg C kg^?1 h^?1 in the warm‐water regime and 369 mg C kg^?1 h^?1 and 439 mg C kg^?1 h^?1 in the cool‐water regime respectively. The FR₉₅ in warm water were achieved at lower POC concentrations than in cool water.     

Effectiveness of copper sulphate,potassium permanganate and peracetic acid to reduce mortality and infestation of Ichthyobodo necator in channel catfish Ictalurus punctatus (Rafinesque 1818)

Ichthyobodo necator is a single‐celled biflagellate parasite, which in high density can cause significant mortality in young fish. Copper sulphate (CuSO₄), potassium permanganate (KMnO₄) and peracetic acid (PAA) were evaluated for effectiveness against ichthyobodosis. Treatments were: untreated control, 2.1 mg L^?1CuSO₄, 3.0 mg L^?1 KMnO₄, 1.5 mg L^?1 PAA and 3.0 mg L^?1 PAA, and were applied to flow‐through tanks on three consecutive days. The study was designed to simulate the flow‐through systems utilized in the commercial rearing of juvenile channel catfish (Ictalurus punctatus). Mortality was monitored daily to compare survival rate among treatments. Parasite intensity was assessed pre chemical exposure and 20–24 h after the third application to determine effectiveness of the treatment. An assessment was also done 7 days post application to investigate possible reoccurrence. Copper sulphate, KMnO₄ and PAA (3.0 mg L^?1) significantly reduced the infestation rate of I. necator. Copper sulphate significantly improved the survival of I. necator infested channel catfish after three flow‐through applications compared with the untreated control. The 3.0 mg L^?1 PAA resulted in significantly lower survival than the untreated control, the 1.5 mg L^?1 PAA and the KMnO₄ were not statistically different from the untreated control.     

Effects of salinity on standard metabolic rate and critical oxygen tension in the giant freshwater prawn (Macrobrachium rosenbergii)

The extensively farmed giant freshwater shrimp, Macrobrachium rosenbergii, can survive salinities up to 26 g L^?1, but the commercially important grow‐out occurs exclusively in freshwater areas. Recent studies suggest the shrimp equally capable of growing in brackish as fresh water and a better understanding of how this species responds to changing salinity could significantly impact freshwater prawn farming in deltas and coastal areas. Here, the effect of salinity (0 and 15 g L^?1) on standard metabolic rate (SMR) and critical oxygen tension (P_crit) was measured in adult M. rosenbergii using intermittent closed respirometry. SMR was 79.8 ± 3.1 and 72.7 ± 2.9 μmol kg^?1 min^?1 in fresh and brackish water, respectively, with no significant difference between the two salinities (P = 0.122). During hypoxia M. rosenbergii maintained oxygen uptake down to a P_crit of 26.3 ± 1.4 mmHg in fresh and 27.2 ± 2.0 mmHg in brackish water (P = 0.682), showing that salinity had no overall effect on oxygen conductance in the animals. These findings are in agreement with recent growth studies and provide further evidence that grow‐out phase could be accomplished in brackish water areas. Thus, the predicted intrusions of brackish water in tropical deltas as a consequence of future global warming may not impact this important production.     

Food consumption, growth and respiration of sole, Solea solea (L.), during early ontogeny in a hatchery environment

Three components of the energy budget, consumption (C), respiration (R) and growth (G). were measured in larval and early juvenile sole (77 μg to 7.2 mg dry weight) kept under controlled temperature (15^oC), light (photoperiod 18 h at 800 lux) and food (Artemici salina. 5 ind ml^-1) conditions. The increase in body weight with age is described by the growth function W_t= 51.9 e^0143t, where t is time in days from hatching. W_t is weight (ug dry wt) at time t, 51.9 is the estimate of larval weight at hatching (Wo) and 0.143 is the instantaneous growth coefficient. Daily food consumption (C, in ug dry wtday”¹ ind^-1) increased with body weight (W, in ug dry wt) according to the allometric function, C = 1.852W^0.852. Low routine oxygen consumption (R, in nl 0₂ h^-1 ind^-1) was best described in relation to body weight by the allometric equation R = 1.47W^0.975 By using the above growth and allometric functions and by converting G, C and R into their energetic equivalents (joules day^-1 ind^-1), the changes in assimilation efficiency (K₁) and gross growth efficiency (K₁) during ontogeny could be modelled.     

Characterization of whitebait (Galaxias maculatus) respiratory rates to optimize intensive culture carrying capacities

Galaxias maculatus is an osmeriform native fish of the Southern Hemisphere, in which the crystalline larvae is considered as a luxury delicacy, for this reason, it has been commercially exploited in Chile, Argentina and New Zealand. However, the fisheries have been rapidly decreasing due to the overexploitation and the predation of introduced species. Because of these events, there is a need to determine a carrying capacity for an intensive fish culture. In order to optimize stocking densities for fish culture, this paper proposes objectives to determine oxygen consumption (OC) rates, dissolved oxygen concentrations that produce signs of hypoxia and the average time elapsed between food intake and peak OC in G. maculatus. In the oxygen experiments under routine metabolism conditions, we found that G. maculatus adults and whitebait showed signs of asphyxia at dissolved oxygen concentrations between 1.3 and 2.2 mg L^?1 and that adults tolerated dissolved oxygen levels as low as 1.3 mg L^?1. The results showed that G. maculatus individuals with an average weight of 0.04 g consumed 0.048 mg O₂ h^?1, whereas individuals with an average weight of 1.4 g consumed 0.345 mg O₂ h^?1. Galaxias maculatus increased the OC rate by 31%, from 0.39 to 0.51 mg O₂ h^?1 g^?1, occurring 14 min after food intake. The carrying capacities for industrial cultures of G. maculatus, were estimated using an allometric equation (OC=0.2363 ×W ^0.612 ), a water flow rate of 1 m³ h^?1 and an input oxygen concentration of 10 mg L^?1 at 12 °C. The density culture of whitebait (4 g) can be allowed to reach 8–11 kg m^?3; therefore, these stocking densities reduce the risk of hypoxia and mortality, ensuring the appropriate growth and feed conversion rates.