Optimization of fertilization rate for maximizing periphyton production on artificial substrates and the implications for periphyton-based aquaculture

The effects of four rates of application of fertilizer, with cow manure (3000 kg ha⁻¹), urea (100 (kg ha⁻¹) and triple super phosphate (TSP) (100 kg ha⁻¹) (treatment F)), treatment F × 0.5 (treatment 0.5F), treatment F × 1.5 (treatment 1.5F) and treatment F × 2 (treatment 2F), on periphyton, plankton and water quality in tropical freshwater ponds were studied. The highest periphyton biomass in terms of dry matter (3.27 mg cm⁻² substrate), ash-free dry matter (2.06 mg cm⁻² substrate) and chlorophyll a (7.49 µg cm⁻² substrate) developed in treatment 1.5F. The ash content of periphyton was lower in treatment 1.5F (38% of dry matter) than in other treatments (57–66% of dry matter). Total ammonia and chlorophyll a of water increased with fertilization rate. Treatment 1.5F (cow manure, urea and TSP at rates of 4500, 150 and 150 kg ha⁻¹ respectively) appears to be the optimum, yielding high quantity and quality periphyton. By supplying a substrate area for periphyton equivalent to the pond surface, it was estimated that this level of fertilization could support a fish production of around 5000 kg ha⁻¹ y⁻¹, without recourse to supplementary food.     

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

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

Optimization of blue mussel (Mytilus edulis) seed culture using recirculation aquaculture systems

By introducing recirculation aquaculture systems (RAS) in the nursery phase of the blue mussel (Mytilus edulis) (17–18 mm), we aimed at a similar growth and survival and a similar water quality compared to the commonly used flow‐through systems (FTS). To calculate water flow and size of the biofilter, a series of experiments were done to determine clearance rate (9.26 mL min^?1), pseudo faeces threshold (60 000 cells Pavlova lutheri mL^?1), nitrogen production (0.00065 mg TAN h^?1 ind^?1 and 1.6 × 10^?5 mg NO₂–N h^?1 ind^?1) and oxygen consumption (0.03 ± 0.01 mg O₂ h^?1 ind^?1). RAS showed no significant differences in water quality (0.06 mg TAN L^?1; 7.7 mg O₂ L^?1) and growth performance of mussel seed specific growth rate (SGR = 5% day^?1) after the experimental period of 4 weeks compared with FTS. The low water refreshment, 10% per day, as well as the constant chlorophyll concentrations (9.76 ± 1.06 μg L^?1), suggests the potential of RAS as culture system for mussel seed.     

Influence of dietary lipid/protein ratio on survival,growth, body indices and digestive lipase activity in Snakehead (Channa striatus,Bloch 1793) fry reared in re‐circulating water system

Nine isoenergetic (18.5 kJ g^?1) diets were formulated in a 3 × 3 factorial design to contain three protein levels (350, 400 and 450 g kg^?1) for each of three lipid levels (65, 90 and 115 g kg^?1), respectively, and fed twice daily for 8 weeks to fish of mean initial weight 3.34 ± 0.02 g reared in a re‐circulatory water system. Temperature, pH and dissolved oxygen (DO) were maintained within the range 28–30 °C, 5.6–6.8 and 4.82–6.65 mg L^?1 respectively throughout. Results show that fish survival was better in the groups fed 65 g kg^?1 lipid while growth performance (% weight gain, WG; specific growth rate, SGR) and nutrient utilization (feed conversion ratio, FCR; protein efficiency ratio, PER; protein intake, PI) in the 65/450 and 90/450 g kg^?1 treatments were similar and significantly (P < 0.05) higher than in fish fed the other lipid/protein ratio combinations. The body indices monitored (Hepatosomatic index, HSI and viscerosomatic index, VSI) were similar among the treatments whereas intestinal lipase activity was not significantly (P < 0.05) affected by increase in dietary lipid and protein levels. Carcass composition showed that dietary protein level affected body protein content positively in the 65 and 90 g kg^?1 lipid treatments, but dietary lipid level did not affect body lipid content. A lipid/protein ratio of 65/450 g kg^?1 is considered adequate for good growth performance and survival of Channa striatus fry.     

Influence of biofilm on the production of <Emphasis Type="Italic">Farfantepenaeus paulensis</Emphasis> in pens in the Patos Lagoon estuary

The objective of the present work was to determine the influence of artificial substrates that increase the area for biofilm development on the production performance of Farfantepenaeus paulensis juveniles in pens. Shrimp were stocked at a density of 20/m² in pen structures (bottom area?=?50 m²) that were installed in the Patos Lagoon estuary. Two treatments with three repetitions were analyzed, where artificial substrates (polyethylene nets—1-mm mesh size) were added to increase the area for biofilm development by 100%, and where no substrates were added. During the experimental period, the biomass and the composition of the biofilm were assessed. After 86 days of rearing, no significant differences were found in shrimp performance between the treatments (p?>?0.05). However, the examination of the chlorophyll a, dry weight, and composition of the biofilm indicated that the shrimp were actively consuming the biofilm attached to the artificial substrates. Significant decreases in the abundances of nematodes >?500 μm after the 56th day and of tintinnids and rotifers between day 28 and day 42, indicated that the shrimp were selectively predating on these organisms. Moreover, a decrease in the chlorophyll a concentration in the biofilm suggests that the shrimp were consuming the microalgae. Although the increase in the area for biofilm development did not improve shrimp performance, the shrimp presented the highest growth rates when they consumed most of the biofilm microorganisms.     

On-farm trials of an integrated fish-cum-poultry farming system using indigenous chickens

The effect of replacing exotic broilers with indigenous chickens in vertically integrated homestead fish ponds as a means of improving the income status of the small-scale farmer was investigated. Ponds integrated at 1000 chickens ha^–1 provided the optimal water quality for fish survival and growth. Excreta load was 3600 kg ha^–1 month^–1 (dry matter); water pH 8.6; total alkalinity 65.0 mg L^–1; dissolved oxygen 8.0 mg L^–1; biochemical oxygen demand (BOD) 2.0 mg L^–1; ammonia 0.02 mg L^–1; total phosphates 10.0 mg L^–1; primary produc tivity 86 mg C m^–2 h^–1); biomass chlorophyll a 9.8 μg cm^–3; and standing crop 2.85 × 10³ cells mL^–1. Fish recovery, weight gain and total yield (18.25 tons ha^–1) for Heterobranchus longifilis, Valenciennes 1840, and 14.90 tons ha^–1 for Oreochromis niloticus (Linnaeus 1758) exceeded the production (3.50 tons ha^–1 and 2.10 tons ha^–1, respectively, for H. longifilis and O. niloticus) from ponds integrated with broiler chicken at the current optimum stocking rate of 1500 chickens ha^–1. Indigenous chickens offered higher resistance, accepted crop wastes and trash as food and generated an excreta load similar to that from more expensive broiler chickens. Economic analysis of the ventures revealed substantial net income at all levels of poultry integration with indigenous chickens as against a net deficit of –=N210 000 ($2470.6) incurred by the farmer using exotic broilers. From a cost–benefit ratio of 1:2.6 in T₂ (1500 indigenous chickens ha^–1) and 1:0.6 in T₄ (1500 broilers ha^–1), a net income of =N1.60 ($0.019) accrued to the farmer from every =N1.0 ($0.01) invested in the integrated system using indigenous chickens as against a net deficit of =N0.40 ($0.005) on invested capital using broiler chickens at the same 1500 chickens ha^–1 level of poultry integration.     

Influence of fish size and water temperature on the metabolic demand for oxygen by barramundi, Lates calcarifer (Bloch), in freshwater

Oxygen demand by all animals is driven primarily by their needs for sustaining metabolism. Typically, larger animals require more oxygen and cellular fuel to carry out respiration than smaller animals. This relationship in most cases is not linear and is usually described by a coefficient and exponent (e.g. ax^b): the exponent b showing the relationship between live‐weight and energy/oxygen demand and is often termed the metabolic body weight (MBW) exponent, while the coefficient (a) tends to be temperature specific and describes the relationship between MBW and maintenance metabolic energy and oxygen demand at that specific temperature. Across all temperatures (range 26.0–32.0°C), the relationship between barramundi (Lates calcarifer) live‐weight (x; g) and relative oxygen consumption as standard metabolic rate (y; mg O₂ kg^?1 h^?1) at 29.4±1.5°C (mean±SD) was described by the exponential curve: y=710.19 x^?0.3268, R²=0.6875 (n=222 assessments). Examination of the same data but on a gross oxygen consumption (mg O₂ h^?1) basis showed a relationship between live‐weight (x; g) and gross oxygen consumption (y; mg O₂ h^?1) that was described by the exponential curve: y=0.710 x^0.6732, R²=0.9033. Evaluation of the combined relationship between fish live‐weight (y; g) and water temperature (x; °C) on gross oxygen consumption rate (z; mg O₂ h^?1) was described by the equation: z=(?20.7818+1.4017x?0.0227x²) ×y^0.673.     

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

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

Dietary lipid concentrations influence growth,liver oxidative stress,and serum metabolites of juvenile hybrid snakehead (<Emphasis Type="Italic">Channa argus</Emphasis> × <Emphasis Type="Italic">Channa maculata</Emphasis>)

The study was conducted to evaluate the effect of dietary lipid levels on growth, liver oxidative stress, and serum metabolites of juvenile hybrid snakehead (Channa argus × Channa maculata). Five isonitrogenous (crude protein 420 g kg^?1) practical diets containing 58, 87, 115, 144, and 173 g kg^?1 crude lipid (named L58, L87, L115, L144, and L173, respectively) were fed to triplicate groups of 30 fish (mean initial weight 24 g) for 8 weeks. The results showed that the final body weight (58.68–78.81 g), specific growth rate (1.41–1.75 % day^?1), and protein efficiency ratio (1.66–2.64) increased significantly with the increasing dietary lipid levels. Liver lipid contents (71.65–101.80 g kg^?1) and crude lipid (52.10–83.63 g kg^?1) of whole body increased with increasing dietary lipid levels and reached the highest values in fish of L173. Fish of L173 showed lower alkaline phosphatase (23.81 King Unit gprot^?1) and catalase activities (4.44 U mgprot^?1) but higher malondialdehyde content (0.69 nmol mgprot^?1) in liver than the other groups. Higher alanine transaminase activity (8.20 U L^?1), aspartate transaminase activity (63.65 U L^?1), and triglyceride (0.29 mmol L^?1) in serum were observed in fish of L173 compared to the other treatments. Fish of L144 showed higher superoxide dismutase activity and glutathione peroxidase activities in liver than that of fish fed diet L58. Fish fed diet L58 showed lower total cholesterol (3.61 mmol L^?1), high-density lipoprotein cholesterol (1.39 mmol L^?1), and low-density lipoprotein cholesterol (0.46 mmol L^?1) in serum. These results suggested that juvenile snakehead (Channa argus × Channa maculata) achieved good growth performance with dietary lipid level 173 g kg^?1. Diet with 143 g kg^?1 lipid was more conductive to liver health. The appropriate dietary lipid supplementation needs to be determined in further studies.     

Dietary copper requirement of fingerling Channa punctatus (Bloch) based on growth,feed conversion,blood parameters and whole body copper concentration

A 12‐week feeding trial was conducted to estimate the dietary copper requirement of fingerling Channa punctatus. Six casein?gelatin‐based test diets (450 g kg^?1 crude protein; 18.81 kJ g^?1 gross energy) with graded levels of copper as copper sulphate (3.7, 4.7, 5.7, 6.7, 7.7 and 8.7 mg copper equivalent kg^?1 diet) were formulated and fed to triplicate groups of fish (7.25 ± 0.81 cm; 5.21 ± 0.27 g) near to satiation. Fish fed diet with 6.7 mg kg^?1 copper had highest absolute weight gain (AWG; 51.63 g fish^?1), protein efficiency ratio (PER; 1.42 g fish^?1), protein gain (PG; 8.34 g fish^?1), haemoglobin (Hb; 9.68 g dL^?1), haematocrit (Hct; 31.18%) and RBCs (3.24 × 10⁶ × mm^?3). Feed conversion ratio (FCR) was found to be best (1.57) at above level of dietary copper. Whole body copper concentration was found to increase with the increasing levels of dietary copper. Hepatic thiobarbituric acid‐reactive substances concentration was found to decrease with increasing dietary concentrations of copper up to 6.7 mg kg^?1 beyond which a reverse trend in this parameter was noted. Broken‐line regression analysis of AWG, FCR and PG concentrations against varying levels of dietary copper yielded the requirement in the range of 6.66–6.78 mg kg^?1. Data generated during this study would be useful in formulating copper‐balanced commercial feeds for the intensive culture of this fish.     

Effects of dietary protein to energy ratios on growth and body composition of juvenile Chinese sucker,Myxocyprinus asiaticus

A growth experiment was conducted to investigate effect of dietary protein to energy ratios on growth and body composition of juvenile Myxocyprinus asiaticus (initial mean weight: 10.04 ± 0.53 g, mean ± SD). Nine practical diets were formulated to contain three protein levels (340, 390 and 440 g kg^?1), each with three lipid levels (60, 100 and 140 g kg^?1), in order to produce a range of P/E ratios (from 22.4 to 32.8 mg protein kJ^?1). Each diet was randomly assigned to triplicate groups of 20 fish in 400‐L indoors flow‐through circular fibre glass tanks provided with sand‐filtered aerated freshwater. The results showed that the growth was significantly affected by dietary P/E ratio (P < 0.05). Fish fed the diets with 440 g kg^?1 protein (100 and 140 g kg^?1 lipid, P/E ratio of 31.43 and 29.22 mg protein kJ^?1) had the highest specific growth rates (SGR) (2.16 and 2.27% day^?1, respectively). However, fish fed the diet with 390 g kg^?1 protein and 140 g kg^?1 lipid showed comparable growth (2.01% day^?1), and had higher protein efficiency ratio (PER), protein productive value (PPV) and energy retention (ER) than other groups (P < 0.05). No significant differences in survival were found among dietary treatments. Carcass lipid content was positively correlated with dietary lipid level, but irrespective of protein level and inversely correlated with carcass moisture content. Carcass protein contents increased with increasing dietary lipid at each protein level. The white muscle and liver composition showed that lipid increased with increasing dietary lipid level (P < 0.05). Dietary protein concentrations had significant effect on condition factor (CF), hepatosomatic index (HSI) and viscerosomatic index (VSI) (P < 0.05). However, dietary lipid concentrations had no significant effect on CF, HSI (P > 0.05). Based on these observations, 440 g kg^?1 protein with lipid from 100 to 140 g kg^?1 (P/E ratio of 29.22 to 31.43 mg protein kJ^?1) seemed to meet minimum requirement for optimal growth and feed utilization, and lipid could cause protein‐sparing effect in diets for juvenile Chinese sucker.     

Mycoflora of the 'green water' culture system of tiger shrimp Penaeus monodon Fabricius

This study was conducted to quantify and characterize the mycoflora associated with the ‘green water’ culture system of Penaeus monodon. Samples of water, tilapia gut and mucus, and shrimp hepatopancreas from three shrimp farms were collected during 15, 30, 45 and 60 days of culture (DOC). Results showed that high fungal loads were observed in tilapia gut (total: 117–1352 colony forming unit (CFU) 5 cm hind gut^?1; yeasts: 0–136 CFU 5 cm hind gut^?1) and mucus (total: 12–311 CFU (5 cm²)^?1; yeasts: 0–88 CFU (5 cm²)^?1), while minimal fungal populations were observed in water samples (total: 0–110CFU mL^?1; yeasts: 0–5 CFU ml^?1). Shrimp hepatopancreas harboured a very low number of filamentous fungi (0–27 CFU 0.1 g^?1) and yeasts (0–7CFU 0.1 g^?1) especially at 60 DOC. The filamentous fungal isolates were dominated by Penicillium and Aspergillus species, while the yeast populations were dominated by Rhodotorula and Saccharomyces species. The dominance of these fungi on tilapia mucus and gut and their presence in the rearing water might play an important role in the overall mechanisms involved in the control of luminous Vibrio in the ‘green water’ grow‐out culture of P. monodon.     

Effect of dietary protein and lipid levels and protein–energy ratio on growth indices, feed utilization and body composition of freshwater prawn, Macrobrachium rosenbergii (de Man 1879) post larvae

A grow‐out experiment was designed to determine the effect of different dietary protein, lipid levels and protein–energy (P:E) ratio on growth performance and feed utilization of the freshwater prawn, Macrobrachium rosenbergii post larvae (PL) culture in pond net enclosures (hapa, 3.75 m^?3 each) for 12 weeks (84 days). The experimental treatments were assigned in triplicate. Six test diets were formulated to contain three different protein levels (300, 350 and 400 g kg^?1 diet) and two lipid levels (100 and 140 g kg^?1 diet) in a factorial manner (3 × 2) to provided six different dietary P:E ratio: 16, 17, 18, 19, 20 and 21 mg CP kJ^?1 g^?1). The result showed that the highest significant (P≤0.05) survival rate, growth indices and feed utilization were observed for M. rosenbergii PL fed a diet with a P:E ratio of 17 mg CP kJ^?1 g¹, whereas, the lowest value was recorded for prawns fed a diet with a P:E ratio of 20 mg CP kJ^?1 g^?1. Whole body contents of protein and lipid were highest (P≤0.05) when fed diets with 21 and 17 mg CP kJ^?1 g^?1 respectively. Concerning dietary protein levels, the highest (P≤0.05) values for survival and growth indices were observed for PL fed a diet containing 300 g kg^?1 diet protein. The same trend was observed for PL fed a diet with 100 g kg^?1 diet lipid level, irrespective of dietary protein levels. A diet containing 300 g kg^?1 protein and 100 g kg^?1 lipid with a dietary P:E ratio of 17 mg CP kJ g^?1 is recommended to stimulate growth performance and nutrients utilization efficiency of M. rosenbergii PL.     

Response of fingerling stinging catfish,Heteropneustes fossilis (Bloch) to varying levels of dietary l‐leucine in relation to growth,feed conversion,protein utilization,leucine retention and blood parameters

Growth response of fingerling Heteropneustes fossilis (6.8 ± 0.2 g; 11.2 ± 0.3 cm) to dietary l ‐leucine levels was assessed by conducting 8‐week feeding trial in a flow‐through system (1–1.5 L min^?1) at 28 °C water temperature. Casein–gelatin‐based isonitrogenous (380 g kg^?1; crude protein) and isoenergetic [17.9 MJ kg^?1; gross energy (GE)] basal diet was supplemented with different levels of l ‐leucine to achieve desired leucine levels ranging between 10 and 22.5 g kg^?1 dry diet. Analysed values were 9.9 (Lc_9.9), 12.4 (Lc_12.4), 15.1 (Lc_15.1), 17.4 (Lc_17.4), 20.1 (Lc_20.1) and 22.4 (Lc_22.4) g leucine kg^?1 diet. Fishes were stocked randomly in quadruplicates and fed to satiation at 07:00 and 17:30 h. Maximum absolute weight gain (AWG g fish^?1), feed conversion ratio (FCR), protein utilization efficiency (PUE%), leucine retention efficiency (LRE%) and haematological parameters were found in fish fed diet Lc_17.4. For precise determination of dietary leucine requirement of Singhi, AWG g fish^?1, FCR, PUE% and LRE% were subjected to broken‐line and second‐degree polynomial regression analysis. Second‐degree polynomial regression analysis fitted the data more accurately (P > 0.05) exhibiting high R² values. Hence, based on this analysis, dietary leucine requirement of fingerling H. fossilis is recommended to be 16.5 g kg^?1 of the diet, corresponding to 43.4 g kg^?1 protein for developing leucine‐balanced commercial feeds.     

Use of artificial substrates to enhance production of freshwater herbivorous fish in pond culture

Two trials were conducted in mud‐bottomed concrete tanks to assess the potential of using artificial substrates to enhance fish production in ponds. Three substrate types were tested: bamboo poles, PVC pipes and sugarcane bagasse bundles. In one trial, periphyton was grown on the substrates in the absence of fish. In the second trial, masheer (Tor khudree Sykes) fingerlings were stocked at three densities. Results showed a significant effect of substrate type on fish growth (P≤ 0.001) and on net fish production (P≤ 0.05), with best growth in the tanks using the bamboo substrate. In the bagasse treatment, 100% fish mortality occurred. Highest extrapolated periphyton‐based gross fish yield (i.e. without feed inputs) was 450 kg ha^?1 90 d^?1 with PVC and 491 kg ha^?1 90 d^?1 with bamboo substrate. The best periphyton growth occurred on bamboo, followed by bagasse and PVC. Without fish, mean periphyton biomass during the culture period was 0.56–1.20 mg cm^?2 on bamboo [ash‐free dry matter (DM)], against 0.09–0.36 mg cm^?2 on PVC and 0.20–0.59 mg cm^–2 on bagasse. No clear effect of fish density or water depth on periphyton biomass could be seen. Only on bamboo, fish density seemed to have a negative effect on periphyton ash‐free dry matter and a positive effect on pigment content (chlorophyll‐a and phaeophytin). Periphyton from bamboo had a lower ash content (38–47% of DM) than from PVC (54–55% of DM) or bagasse (51–58% of DM). It is concluded that substrate type has a strong effect on periphyton productivity and composition, and on fish productivity. Good fish production was achieved without feed inputs. More research is needed to study the economic viability of periphyton‐based systems in the context of Indian aquaculture.     

Performance evaluation of concurrent rice–fish–prawn culture with and without cull harvesting

This study was carried out in farmers' fields for three experimental culture cycles to evaluate the performance of rice–fish–prawn culture. The treatments carried out were deepwater rice mono‐cropping (R), and rice–fish–prawn culture with cull harvesting (R–FC) and without cull harvesting (R–F). Water pH and total alkalinity were significantly higher (P<0.05) in R–FC than in R–F, while the concentrations of total suspended solids, plankton and chlorophyll a were higher in R–F. Cull harvesting in R–FC had no marked influence on the concentrations of dissolved oxygen, NH₄⁺, nitrite, nitrate and phosphate compared with the R–F treatment. The significantly higher fish and prawn yields (P<0.05) and species‐wise faster individual growth performance in R–FC than in R–F were probably due to periodic cull harvesting, which minimized the competition for food and space as well as physiological stress at reduced density. The paddy yield and percentage increase in paddy yield over rice mono‐crop was significantly higher (P<0.05) in R–FC (25%), followed by R–F (16.9%), probably due to lower chlorophyll a (36.7 mg m^?3) and plankton density (1.4 × 10⁴ L^?1), which minimized the competition for nutrients with rice plants. The highest rice equivalent yield (38.5), output value–cultivation cost ratio (1.56) and enhanced net return (28%) in deepwater rice–fish culture were recorded when cull harvesting was practiced.     

Effect of dietary protein and lipid levels on growth and body composition of juvenile turbot (Scophthalmus maximus L) reared under optimum salinity and temperature conditions

Effect of dietary protein and lipid levels on growth and body composition of juvenile turbot was determined at optimum salinity and temperature conditions of 17 g L^?1 and 19.2 °C, respectively, by using 3 × 2 (protein levels: 550, 600 and 650 g kg^?1; lipid levels: 69 and 168 g kg^?1) factorial design with three replications of each. Fish were hand‐fed to satiety twice daily throughout the feeding trial. Weight gain and specific growth rate of fish were significantly (P < 0.05) increased with increased dietary lipid level, but not by dietary protein level. Daily feed intake was significantly (P < 0.05) affected by both dietary protein and lipid levels. Feed efficiency ratio and protein efficiency ratio were significantly (P < 0.05) affected by dietary lipid level, but not by dietary protein level. Moisture content of whole body was significantly (P < 0.05) affected by dietary lipid level, but not by dietary protein level. Crude lipid content of whole body was significantly (P < 0.05) affected by dietary lipid level, but not by dietary protein level. Significantly higher 20:5n?3, 22:6n?3 and n?3 highly unsaturated fatty acids were observed in turbot fed the low lipid diet than fish fed the high lipid diet in all protein levels, but significantly lower 18:2n?6 was observed in fish fed the former compared with the latter. In considering results of growth, specific growth rate and efficiency of feed, optimum dietary protein and lipid levels for juvenile turbot seemed to be 550 and 168 g kg^?1 of the diet, respectively, under optimum salinity and temperature conditions.     

A multivariate approach to optimization of macronutrient composition in weaning diets for cod (Gadus morhua)

Atlantic cod, initial weight 0.26 g, were fed diets varying in added protein from 530 to 830 g kg^?1, lipid from 50 to 300 g kg^?1 and carbohydrate from 0 to 150 g kg^?1 of dry weight, according to a three‐component mixture design. Analysed values of protein and lipid were 500–770 g kg^?1 and 30–270 g kg^?1, respectively. Analysed carbohydrate levels were as added. Increasing levels of both lipid and carbohydrate had a positive effect on fish growth (P < 10^?3), whereas protein levels above 600 g kg^?1 gave a reduction in growth (P < 10^?4). The effects on growth were evident in fish less than 4 g, whereas fish growth between 4 and 6 g was unaffected by the dietary variation. It is hypothesized that the reduction in growth at high protein levels in fish of less than 4 g could be owing to incomplete utilization of protein, as the stomach of cod is not fully developed before the fish is approximately 1 g. Mortality and cannibalism were high in fish less than 4 g but low when the fish grew from 4 to 6 g. There was a significant decrease in cannibalism with increasing dietary lipid during the first half of the experiment (P < 0.05) and cannibalism was consistently high in fish fed less than 150 g kg^?1 lipid. The lipid level in whole fish increased with increasing dietary levels of lipid (P < 10^?6) and carbohydrate (P < 10^?4), whereas the liver lipid level increased with increasing dietary lipid up to 200 g kg^?1 (P < 10^?6) and decreased thereafter (P < 10^?4). Whole body glycogen increased slightly with increasing levels of dietary carbohydrate (P < 0.05) and was not affected by the other dietary variables. Liver glycogen increased in response to increasing dietary carbohydrate (P < 10^?5) and decreasing levels of dietary lipid (P < 10^?5). An abrupt increase in liver glycogen was seen with the reduction in dietary lipid from 100 to 50 g kg^?1. The hepatosomatic index increased in response to both dietary lipid and carbohydrate (P < 10^?6). It is concluded that the protein requirement of young cod is less than 500 g kg^?1 of dry diet. Fish of less than 4 g should not be given more than 620 g kg^?1 protein and should be supplemented with 150–200 g kg^?1 lipid. Carbohydrate up to 150 g kg^?1 of dry diet promoted growth and did not seem to affect the fish negatively. Fish above 4 g can be given diets varying in protein and carbohydrate over the wide range of concentrations used in the present study, but lipid supplementation should be restricted to between 100 and 200 g kg^?1.     

Optimum dietary protein and lipid specifications for grow-out of humpback grouper Cromileptes altivelis (Valenciennes)

Fingerling Cromileptes altivelis of less than 50 g have been shown to require feeds of 50–56% crude protein (CP) and 9–15% lipid. The requirements of larger, market‐size fish have not been reported. A total of 324 hatchery‐produced C. altivelis were weight sorted into three groups of 136, 175 and 225 g start weight and equally (12 seacage^?1) and randomly distributed to floating net seacages in accordance with a 3 × 3 factorial arrangement of CP (42%, 47% or 53%; estimated digestible CP of 40%, 46% or 52%) and lipid (8%, 12% or 16%; equivalent to estimated digestible energy (DE) contents of 14.0, 15.8 or 17.5 MJ kg^?1). Changes in dietary CP and lipid content were achieved at the cost of wheat flour by proportionally varying the protein mixture (essentially a 0.62:0.22:0.16 ratio of fish meal, mysid meal and casein respectively) and oil mixture (a 2:1 ratio of fish oil and soybean oil respectively). Fish were fed twice daily to satiation for 180 days. There was no significant (P>0.05) interaction between the main effects of dietary protein and lipid for any growth, nutrient retention or whole‐body composition measurements. Increasing dietary CP significantly improved the survival rate (80.6%, 88.9% and 87.0%), specific growth rate (SGR; 0.24%, 0.28% and 0.31% day^?1), feed conversion ratio (FCR; 2.77, 2.21 and 2.00) and DE retention (18.2, 21.3 and 23.2%), respectively, but did not significantly affect digestible protein retention. Increasing dietary lipid increased SGR (0.25, 0.29 and 0.29% day^?1) and the whole‐body lipid (and energy) composition, and reduced the survival rate (87.0%, 88.9% and 80.6%), respectively, but FCR and retentions of digestible protein and DE were not significantly affected. These results indicate that humpback grouper of 150–400 g require a dietary specification of not less than 51% digestible protein (～53% CP), 10–12% lipid and digestible protein:DE of 31–32 g MJ^?1 for optimal growth.     

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.