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.     

Effects of water temperature and body weight on anaesthetic efficiency in marbled rabbitfish (Siganus rivulatus)

The effects of four anaesthetic agents, tricaine methanesulphonate (MS‐222) (112.5 mg L^?1), 2‐phenoxyethanol (400 μL L^?1), clove oil (70 mg L^?1) and benzocaine (65 mg L^?1) on juvenile marbled spinefoot (Siganus rivulatus) of three mean body weights (7.3 g, 19.1 g, 55.5 g) and at three temperatures (20, 25, 30°C) were evaluated. In addition, the relationship between body lipid content and efficacy of the four anaesthetic agents was evaluated in juvenile S. rivulatus. Times necessary for induction and recovery were recorded. Significant effects of temperature on induction and recovery times were observed. Induction and recovery times decreased with increasing water temperature. No uniform relationship between body weight of juvenile marbled spinefoot and anaesthetic efficacy was observed. Body fat content was positively correlated with induction time only when MS‐222 was used but did not affect induction times of fish exposed to 2‐phenoxyethanol, clove oil or benzocaine. Recovery times were generally longer for all fish containing more body fat. Results of the study show that anaesthetic efficiency increases with increasing water temperature but is not strongly affected by body weight for juvenile marbled spinefoot. In addition, body fat in fish affected the efficacy of the various anaesthetic agents tested in this study, generally slowing down recovery.     

Acute and chronic effects of aqueous ammonia on marbled spinefoot rabbitfish,Siganus rivulatus (Forsskål 1775)

Ammonia is a metabolite of aquatic organisms which might reach deleterious levels in intensive fish farms. The aim of the present study was to determine median lethal concentrations (96‐h LC₅₀) of total ammonia nitrogen (TA‐N) on marbled spinefoot rabbitfish (Siganus rivulatus) and chronic effects of TA‐N on survival, growth and behaviour of juvenile rabbitfish over a 50 day period. In the first experiment, fish were exposed to 0, 2, 4, 6, 8, 10, 12, 14, 16, 18 and 20 mg L^?1 TA‐N for 96 h and survival evaluated. In the second experiment, 12 fish were stocked per 50‐L tank and treated with one of 0, 2, 4, 6, 8, 10 and 12 mg L^?1 TA‐N with three replicate tanks per treatment. Survival and growth were determined and histopathological alterations of gills due to chronic ammonia exposure were studied by light and electron microscopy. The 96‐h LC₅₀ values were 16–18 mg L^?1 TA‐N. In the chronic exposure experiment, fish reared in water with 0 mg L^?1 TA‐N had 100% survival and had 50% weight increase in 50 days. Fish at 2 and 4 mg L^?1 TA‐N all died whilst fish in 6, 8, 10 and 12 mg L^?1 TA‐N survived and grew albeit less than in treatment 0 mg L^?1. Gills from ammonia treated fish displayed severe histological and ultrastructural alterations including hyperplasia, hypertrophy and fusion of secondary lamellae, aneurysms and presence of pleomorphic altered cells. Chronic exposure to ammonia is deleterious to marbled spinefoot rabbitfish and low concentrations of ammonia appear to kill the fish in <50 days whilst fish can survive for more than 50 days at concentrations between 6 and 12 mg L^?1 TA‐N.     

Dietary protein requirement of juvenile marbled spinefoot rabbitfish Siganus rivulatus

Rabbitfish are an Indo‐Pacific herbivorous marine fish that have good market demand and are suitable for aquaculture. The present work was performed to determine dietary protein inclusion necessary for optimal growth of juvenile rabbitfish Siganus rivulatus. Six diets with increasing levels of protein (10, 20, 30, 40, 50 and 60 g crude protein 100 g^?1 feed) and similar levels of gross energy (20 MJ kg^?1) were prepared and offered to S. rivulatus juveniles maintained in triplicate cages placed in two large water tanks for 49 days. Growth progressively improved with dietary protein for fish offered diets from 10% to 40% protein inclusion. Diets with greater protein levels did not improve fish growth beyond that observed in the 40% group. Daily feed intake, apparent protein utilization and feed conversion ratio decreased as dietary protein increased. Protein efficiency (PE) was greatest (1.47) in fish offered the 10% protein diet and least in fish offered the 60% protein diet (0.80). No differences in PE were observed among all other treatments (20–50%). Results of the present work suggest that minimum dietary requirement for suitable growth of S. rivulatus juveniles is 40% protein when digestible energy of the diet is 16–18 MJ kg^?1.     

Effects of temperature on survival and growth of juvenile spinefoot rabbitfish (Siganus rivulatus)

Interest in culturing marbled spinefoot rabbitfish Siganus rivulatus is increasing in countries on the Eastern Mediterranean, Red Sea and Arabian Gulf. However, information on environmental tolerances and requirements for optimal growth are scarce. In the present work, the temperature requirements for spinefoot rabbitfish were investigated in two experiments. In the first experiment, juvenile rabbitfish were distributed into eight 180 L square tanks at 12 fish per tank. The temperature in four tanks was reduced at a rate of 1 °C day^?1 and in four tanks was increased by 1 °C day^?1 until the fish stopped feeding. Minimum and maximum temperatures for feeding were recorded. In the second experiment, the fish were placed in four temperature treatments (17, 22, 27, 32 °C) at four replicates per treatment for 8 weeks. Survival and growth were evaluated. Fish stopped feeding at 14 and 36 °C. Their maximum growth rate was at 27 °C, and survival was 100% in all treatments. The relationship between specific growth rate and temperature was parabolic, described by the equation: SGR=?0.0014 (T³)+0.0798 (T²)?1.3089 (T)+6.7342. The results show that S. rivulatus is a eurythermal fish whose optimal temperature for growth is circa 27 °C.     

Effects of stocking density on the survival, growth, size variation and condition index of juvenile rabbitfish Siganus rivulatus

Spinefoot rabbitfish, Siganus rivulatus, is an economically important species of herbivorous fish that is relatively easy to rear and thus considered to be suitable for aquaculture. Juveniles are generally reared in nursery systems before being stocked into growout cages or ponds. We report here our evaluation of the effects of stocking density on the survival, growth, feed efficiency and condition index of S. rivulatus juveniles in nursery tanks. The experiment was conducted in a recirculating system of twelve 52-l aquaria connected to a biological filter and a sand filter. Juvenile fish (average weight 6.5 g) were stocked into aquaria at four stocking densities (10, 20, 30, and 40 fish/aquarium) with three replicate aquaria per treatment. Diet was provided at 3% body weight daily divided into two feedings. Fish were weighed weekly for 8 weeks and the diet increased accordingly. Survival was greater than 95% in all treatments, with no significant differences observed among treatments. There were also no differences in specific growth rate (SGR 2.12–2.27) of the fish among treatments. Growth rate was linear during the 8 weeks in all treatments, and harvested biomass increased proportionally to stocking density (198, 401, 600 and 785 g per increasing stocking density, respectively). Feed efficiency (FE 0.67–0.71) of the fish did not vary significantly among treatments. The coefficient of variation was high (35–41%) among the harvested fish, but it also did not differ significantly among treatments. The final condition indices of the fish in all treatments were similar to each other but significantly greater than the initial values (P < 0.05). The results suggest that there is no apparent effect of stocking density at the levels tested on the survival and growth of juvenile rabbitfish.     

Feed regimen affects growth,condition index,proximate analysis and myocyte ultrastructure of juvenile spinefoot rabbitfish Siganus rivulatus

The present work was designed to evaluate the effects of various feeding regimens on rabbitfish growth and condition. Twelve juvenile rabbitfish Siganus rivulatus (7.3 ± 0.1 g) were stocked into each of 15 tanks. Tanks were randomly assigned one of five treatments with three replicate tanks per treatment. Treatments were G‐I: fish fed once daily at 08.00; G‐II: fish fed once daily at 17.00; G‐III: fish fed twice daily at 08.00, 17.00; G‐IV: fish fed three times daily, at 08.00, 13.00, 17.00; G‐V: fish fed three times daily at 08.00, 13.00, 17.00 for six consecutive days, followed by 1 day of fasting. Fish were offered a commercial diet (Golden Extruded, 450 g kg^?1 protein, 200 g kg^?1 lipids) to apparent satiation. At the conclusion of the study, weight gain of rabbitfish fed three times daily (273.1%) was significantly greater than weight gain of fish in all other treatments. Feed conversion ratio (FCR) of fish fed once per day (1.5) was significantly greater than FCR in all other treatments. Proportion of lipids in fish fed three times per day was significantly greater than in fish from other treatments. Ultrastructure of muscle of fish offered feed three times daily had a better organized appearance and better defined striation than muscle of fish in other treatments. Accordingly, feeding rabbitfish three times daily is better than feeding them once or twice daily and also improves muscle ultrastructure and quality.     

Assessing the use of a dietary probiotic/prebiotic as an enhancer of spinefoot rabbitfish Siganus rivulatus survival and growth

The use of prebiotics and probiotics as feed supplements that improve efficiency of intestinal bacteria is becoming de rigueur in animal husbandry in many regions worldwide. We tested the effects of a commercial probiotic (Biogen^®) containing allicin, high unit hydrolytic enzyme, Bacillus subtilis spores and ginseng extracts on survival, growth, carcass composition and feed cost/benefit in rabbitfish Siganus rivulatus. Fifteen net cages (100 × 100 × 40 cm; L × W × H) were stocked with 10 juvenile rabbitfish (10.3 g per fish) each and placed in a large rectangular tank and offered feed at 4% body weight daily. Cages were offered one of five isonitrogenous and isocaloric diets containing 0, 1, 2, 3 and 4 g kg⁻¹ probiotic at three replicates per treatment for 98 days. Fish in all cages were weighed at 2‐week intervals and feed regimen was adjusted accordingly. Rabbitfish offered the control diet exhibited lower growth and feed utilization than all experimental treatments. There was no effect of probiotic inclusion level on survival but growth was better at all inclusion levels than in the control. No significant differences (P > 0.05) in growth were observed among fish groups fed various levels of the probiotic. Carcass composition was not affected by dietary probiotic inclusion. Ultimately, when all variables are considered, Biogen^® inclusion to diets appears to reduce feed cost per unit growth of rabbitfish.     

Optimum protein-to-energy ratio for two size groups of rabbitfish, Siganus canaliculatus (Park)

Three approximately isoenergetic (17 kJ g^?1) diets were formulated with dietary protein levels of 270, 360 and 480 g kg^?1 (DM basis) providing protein-to-energy ratios of 15.69, 20.48 and 27.16 mg crude protein (CP) kJ^?1, respectively. The effects of these diets on several growth and nutritional parameters were evaluated for the fry (2.50 ± 0.184 g) and fingerlings (11.53 ± 0.023 g) of Siganus canaliculatus (Park). Maximum growth and best feed utilization efficiency of fry were obtained using the diet containing 480 g kg^?1 protein and P:E ratio of 27.16 mg CP kJ^?1. For fingerlings the best results were obtained with the diet containing 360 g kg^?1 protein and P:E ratio of 20.48 mg CP kJ. Body composition of the fry was not affected by the feeding regime whilst the effect was evident in the fingerling groups. The carcass protein content of the fingerling was observed to increase with increasing P:E ratios while lipid content decreased as P:E increased.     

Effect of dissolved oxygen levels on growth performance,energy budget and antioxidant responses of yellow catfish,Pelteobagrus fulvidraco (Richardson)

This study was conducted to determine the effect of dissolved oxygen (DO) levels on growth performance, energy budget and antioxidant responses of yellow catfish Pelteobagrus fulvidraco. Yellow catfish was exposed to four levels of DO, consisting of hypoxia (2.28 mg L^?1), moderate hypoxia (4.04 mg L^?1), saturation (6.51 mg L^?1) and super‐saturation groups (9.11 mg L^?1), respectively, for 8 weeks. Specific growth rate and feed efficiency in dry matter were lowest in hypoxia and highest in the saturation and super‐saturation groups. Apparent digestibility coefficients of dry matter and energy increased with increasing DO levels. Gross energy and growth energy were lowest for hypoxia, followed by moderate hypoxia and the highest for other two groups. Faecal energy was highest in hypoxia and lowest in saturation and super‐saturation group. DO levels also significantly influenced activities of antioxidant enzymes and malondialdehyde level in liver and serum. Based on the observation described previously, saturated DO level helps to improve growth performance, feed utilization and antioxidant responses in yellow catfish. Super‐saturation did not increase fish performance. To our knowledge, this is the first study involved in the effect of DO levels on energy budget of fish and provides new insight into aeration regime for yellow catfish culture.     

Histological evidence of lunar-synchronized ovarian development and spawning in the spiny rabbitfish Siganus spinus (Linnaeus) around the Ryukyus

ABSTRACT: This study clarifies the annual reproductive cycle and the lunar-synchronized spawning of the spiny rabbitfish ( Siganus spinus ) that inhabit the Okinawan waters. Annual and weekly changes in the gonadosomatic index (GSI) and the histological features of the ovaries were checked. Gonadosomatic index was high during the months of May to July, and yolk-laden oocytes were observed in the ovaries from March to July. Some of the ovaries collected during June and July contained oocytes at maturation stage or ovulatory follicles. These results suggest that the spiny rabbitfish undergo active vitellogenesis and spawning from May to July. During the reproductive season (May to July), collection of fish according to the lunar phase revealed that a high GSI occurred around the time of the new moon. Cyclic oocyte development with peaks around the time of the same moon phase was also observed, suggesting that, in Okinawan waters, this species is a lunar-synchronized spawner and spawns three times.     

Feed intake,growth and metabolism of Nile tilapia (Oreochromis niloticus) in relation to dissolved oxygen concentration

The objectives of the present study were to determine, for Nile tilapia of different body weights and fed to satiation, (1) the incipient dissolved oxygen (DO) concentration at which feed intake starts to level off and (2) the effect of DO on nitrogen and energy balances. Two successive experiments were conducted with two weight classes of male Nile tilapia (>200 g, Experiment 1, and <100 g, Experiment 2). Twelve aquaria were assigned to four DO levels in each experiment. Fish were fed to apparent satiation for 16 and 20 days in Experiments 1 and 2 respectively. The DO‐feed intake curve of fish<100 g appeared to level off at a DO of 3 mg L^?1, while that of fish>200 g continued to increase as DO increased from 2.6 to 6.0 mg L^?1. The latter curve suggests that the incipient DO for fish>200 g is about 5.5 mg L^?1. Fish tended to reduce the energy requirement for maintenance as DO declined. A DO reduction caused an increase in the apparent digestibility coefficient (ADC), but further declines in DO to levels below a critical level decreased ADC. The DO did not have a considerable effect on the metabolizable energy: digestible energy ratio of the diet.     

Anaesthetic efficacy of clove oil,benzocaine, 2‐phenoxyethanol and tricaine methanesulfonate in juvenile marbled spinefoot (Siganus rivulatus)

Anaesthetics are used in aquaculture and fisheries to facilitate routine procedures, such as capture, handling, transportation, tagging, grading and measurements that can often cause injury or induce physiological stress. Two experiments were performed to assess the efficacies of four anaesthetic agents, clove oil, benzocaine, 2‐phenoxyethanol and MS‐222 on juvenile marbled spinefoot rabbitfish (Siganus rivulatus). In the first experiment we tested the lowest effective doses that produced induction and recovery times in 3 min or less and 5 min or less respectively. Dosages were 70 mg L^?1 for clove oil, 60–70 mg L^?1 for benzocaine, 400 μL L^?1 for 2‐phenoxyethanol and 100–125 mg L^?1 for MS‐222. In the second experiment, we determined optimal concentrations of the four anaesthetics if they were to be used to transport rabbitfish fry. Anaesthetic concentrations suitable for handling and transport were: 10–15 mg L^?1 of MS‐222, 5–10 mg L^?1 of benzocaine, 5 mg L^?1 of clove oil and 50–100 μL L^?1 of 2‐phenoxyethanol. All anaesthetic agents are acceptable for use on S. rivulatus, however, 2‐phenoxyethanol, MS‐222 and clove oil appear to be more suitable than benzocaine. Further studies need to be conducted on effects of high and low doses of anaesthetic agents on physiology of marbled spinefoot.     

Moderate salinities enhance growth performance of Nile tilapia (Oreochromis niloticus) fingerlings in the biofloc system

The biofloc technology (BFT) has recently gained attention as an economic and environmentally sustainable system for aquaculture. The use of BFT with salinized water could be used to minimize the negative effects of nitrogenous waste and improve the growth performance of Nile tilapia. This work evaluated the growth performance, survival, gill lesions, and fillet composition of tilapia fingerlings (Oreochromis niloticus) reared during 70 days with different salinities (0, 4, 8, 12, and 16 g/L) in a biofloc previously developed. The results indicated that the use of mature bioflocs alone was sufficient to avoid fingerling mortality due to nitrite peaks. Moreover, the salinized water, especially between 4 and 8 g/L (maximum points around 6 g/L), can be recommended in BFT to improve the growth performance of tilapia in the initial culture phase. The salinity level that was evaluated did not affect fillet composition nor the occurrence of gill lesions. The total ammonia nitrogen concentration was lower in freshwater than in salinized water (p < 0.05). Nitrite peaks in salinities of 12 and 16 g/L appeared later and were higher in comparison to other treatments. Considering minimal water exchange in BFT, the use of salinized water in this system may be environmentally viable.     

Effects of dissolved oxygen on the growth performance,haematological parameters,antioxidant responses and apoptosis of juvenile GIFT (Oreochromis niloticus)

This study investigated the effects of different dissolved oxygen (DO) levels on the growth performance, antioxidant response and apoptosis of juvenile GIFT (genetically improved farmed tilapia, Oreochromis niloticus). GIFT were fed with five DO levels (1, 2, 3, 4 and 5 mg/L) for 60 days, and the results showed that the final body weight, weight gain rate, specific growth rate and crude protein and crude lipid contents of the fish muscle increased at 5 mg/L DO. The activities of the antioxidant and digestive enzymes were significantly up‐regulated with increasing DO levels. However, the haemoglobin content, number of red blood cells, malondialdehyde content, transaminase activities, glucose content and lactic acid levels decreased at higher DO levels. Furthermore, the cardiomyocyte apoptotic index was significantly decreased with increasing DO levels. Our results show that 5 mg/L DO improved growth performance, promoted antioxidant enzyme activities and reduced liver damage in GIFT.     

Survival of Diploid and Triploid Rhamdia quelen Juveniles Under Different Oxygen Concentrations

The objective of this study was to determinate the lethal concentration of dissolved oxygen (DO) over 96 hours of exposure (LC50–96h) for diploid and triploid jundia Rhamdia quelen juveniles. Diploid and triploid fish weighing approximately 4 g were subjected to DO concentrations varying between 0.4 and 1.3 mg O₂ L^?1; water temperature was maintained at 27?°C and pH at 6.3. The LC50–96h for diploids of Rhamdia quelen was 0.535 mg O₂ L^?1, while the value obtained for triploids was 6% greater. These results demonstrated that triploids of Rhamdia quelen juveniles have greater sensitivity to hypoxia compared to diploids.     

Effects of dissolved oxygen and dietary lysine levels on growth performance,feed conversion ratio and body composition of grass carp,Ctenopharyngodon idella

In order to investigate the effects of lysine and dissolved oxygen on grass carp, the grass carp were fed with 13, 15 and 17 g kg ⁻¹ lysine diet at about 6 mg L⁻¹ (high dissolved oxygen, HO group) or 3.5 mg L⁻¹ (low dissolved oxygen, LO group) dissolved oxygen level, for 8 weeks. The fish were fed to apparent satiation by hand. The results showed that apparent digestibility of protein, energy and dry matter were decreased significantly when grass carp were fed at 3.5 mg L⁻¹ dissolved oxygen, and feed intake (FI) was also inhibited by low dissolved oxygen (P < 0.05). Weight gain, protein retention, protein efficiency, feed conversion ratio and amino acid retention of fish at 6 mg L⁻¹ dissolved oxygen level were significantly improved at 3.5 mg L⁻¹ dissolved oxygen level (P < 0.05). Weight gain, protein and amino acid retention, and feed efficiency of grass carp at the two dissolved oxygen levels were significantly improved by lysine supplementation (P < 0.05). The dietary lysine level and dissolved oxygen of water had an interaction effect on feed conversion ratios (P < 0.05). Grass carp fed at low dissolved oxygen level showed lower liver protein and fat contents. Plasma aspartate aminotransferase (AST) activity of grass carp fed at 3.5 mg L⁻¹ dissolved oxygen level was significantly increased compared to 6 mg L⁻¹ dissolved oxygen level (P < 0.05). Our results show that low dissolved oxygen level of water is harmful to the liver of grass carp.     

Stocking density effects on growth and production of the threatened silurid catfish,Mystus cavasius (Hamilton) fingerlings in nursery ponds

The fingerling‐rearing experiment of the threatened catfish, Mystus cavasius was carried out at different stocking densities in earthen nursery ponds. Twelve‐day‐old fry were stocked at 200 000 ha^?1 in treatment‐1 (T₁), 250 000 ha^?1 in treatment‐2 (T₂) and 300 000 ha^?1 in treatment‐3 (T₃) respectively. The mean length and weight of fry at stocking was 1.24 ± 0.25 cm and 0.11 ± 0.04 g respectively. Fry in all the experimental ponds were supplemented with SABINCO nursery feed for the first 14 days and starter‐I feed for days 15–56. The physico‐chemical parameters and plankton population of pond water were within the suitable level for fish culture. Growth in terms of final weight, final length, weight gain, length gain and specific growth rate and survival of fingerlings were significantly higher in T₁ than those in T₂ and T₃. Feed conversion rate was significantly lower in T₁ followed by T₂ and T₃ in that order. Significantly higher number of fingerlings was produced in T₃ than that in T₂ and T₁. Even then, consistently higher net benefits were obtained from T₁ than those from T₃ and T₂. Among the treatments evaluated, 200 000 fry ha^?1 was the best stocking density considering the highest growth, production and net benefits of fingerlings of M. cavasius in nursery ponds.