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.     

Effects of stocking density on production and economics of Nile tilapia (Oreochromis niloticus) and freshwater prawn (Macrobrachium rosenbergii) polyculture in periphyton-based systems

The present research investigated the effect of stocking density on pond (75 m², depth 1.2 m) production of Nile tilapia (Oreochromis niloticus) and freshwater prawn (Macrobrachium rosenbergii) stocked at a fixed 3:1 tilapia:prawn ratio. Three stocking densities were tried in triplicate: 20 000 ha⁻¹ (treatment TP‐20), 30 000 ha⁻¹ (TP‐30) and 40 000 ha⁻¹ (TP‐40). The ponds were provided with bamboo as substrate for periphyton development. Bamboo poles (mean diameter 5.5 cm and 5.0 poles m⁻²) were posted vertically into pond bottoms, resulting in 60% additional substrate area in each pond. On average, 43 genera of algae and 17 genera of zooplankton were identified from pond water, whereas 42 genera of algae and six genera of microfauna were attached to bamboo substrates. No differences were observed between treatments in the ash‐free dry matter (AFDM), chlorophyll a and phaeophytin a content of periphyton (P>0.05). Survival of tilapia and prawn and individual weight gain of tilapia were lower (P<0.05) in treatment TP‐40. The net yields were higher (P<0.05) in treatments TP‐30 (2209 and 163 kg ha⁻¹ 105 day⁻¹ of tilapia and prawn respectively) and TP‐40 (2162 and 141 kg ha⁻¹ of tilapia and prawn respectively) than in treatment TP‐20 (1505 and 136 kg ha⁻¹ of tilapia and prawn respectively). The net tilapia yields were quadratic correlated (R²=0.92) with fish stocking density. The cost–benefit analysis shows that the net profit margin was highest in treatment TP‐30 (69%), followed by TP‐20 (50%) and TP‐40 (44%).     

Planktonic and Biochemical Composition of Periphyton Grown on Some Biodegradable and Non-Degradable Substrates

ABSTRACT

Ten locally available substrates, five biodegradable and five non-degradable, were evaluated for their potential to harbor periphyton in cement tanks fertilized with poultry manure. The tanks were fertilized regularly and the periphyton was allowed to grow for 70 days. Weekly samples of periphyton and plankton were collected for enumeration and biochemical analyses. Among the substrates, earthen tiles harbored negligible amount of periphyton. The phytoperiphyton genera encountered on the substrate belonged mainly to Chlorophyceae (14 genera), followed by Cyanophyceae (2 genera), Chrysophyceae (1 genus), Bacillariophyceae (1 genus), and Dinophyceae (1 genus). Nauplius, Keratella, Diaptomus, Cyclops, Moina, Chironomus and insect eggs were the zooplankton encountered on substrates. Phytoplankton density was higher on tyre (86,426 cells or colonies/cm²) and palm leaf (85,808 cells or colonies/cm²) and lowest on ceramic tile (21,081 cells or colonies/cm²). Glass plates harbored the highest number of zooplankton species per unit area (1050 cells or colonies/cm²), while arecanut leaf-sheath had the lowest (210 cells or colonies/cm²). All five families of phytoplankton present on the substrates were also present in tank water. While periphyton contained 26 genera, tank water had only 24. Periphytic dry matter, ash, ash-free dry matter, plankton density on substrates and water showed a general increase with respect to time. Polyvinyl chloride (PVC) (0.972 mg/cm²), glass (0.913 mg/cm²), and bamboo (0.897 mg/cm²) had higher periphytic dry matter and ceramic tile (0.262 mg/cm²) the lowest. All the proximate composition parameters of periphyton, except nitrogen free extract (NFE) varied significantly (P < 0.05) between the substrates. The moisture content of periphyton ranged from 85.58% (bamboo) to 95.27% (arecanut leaf-sheath). Crude protein was high in periphyton from bamboo (3.77%) and tyre (3.66%) and low in that from arecanut leaf-sheath (0.99%).     

The potential of mixed culture of genetically improved farmed tilapia (Oreochromis niloticus) and freshwater giant prawn (Macrobrachium rosenbergii) in periphyton-based systems

The production performance of genetically improved farmed tilapia (GIFT, Oreochromis niloticus) and freshwater prawn (Macrobrachium rosenbergii) in periphyton‐based systems were studied in farmers' ponds at Mymensingh, Bangladesh. Fifteen ponds (200–300 m² area and 1.0–1.5 m in depth) were used to compare five stocking ratios in triplicate: 100% GIFT, 75% GIFT plus 25% prawn, 50% GIFT plus 50% prawn, 25% GIFT plus 75% prawn and 100% prawn. Ponds were stocked at a total density of 20 000 GIFT and/or prawn ha^?1. Bamboo poles (mean diameter 6.2 cm and 5.5 pole m^?2) were posted in pond bottoms vertically as periphyton substrate. Periphyton biomass in terms of dry matter (DM), ash‐free DM and chlorophyll a were significantly higher in ponds stocked with prawn alone than in ponds with different combinations of GIFT and prawn. Survival of GIFT was significantly lower in ponds stocked with 100% GIFT (monoculture) whereas, that of prawn was significantly higher in its monoculture ponds indicating detrimental effects of GIFT on prawn's survival. Individual weight gains for both species were significantly higher in polyculture than in monoculture. The highest total fish and prawn yield (1623 kg GIFT and 30 kg prawn ha^?1) over 125–140 days culture period was recorded in ponds with 75% GIFT and 25% prawn followed by 100% GIFT alone (1549 kg ha^?1), 50% GIFT plus 50% prawn (1114 kg GIFT and 68 kg prawn ha^?1), 25% GIFT plus 75% prawn (574 kg GIFT and 129 kg prawn ha^?1) and 100% prawn alone (157 kg ha^?1). This combination also gave the highest economic return. Therefore, a stocking ratio of 75% GIFT plus 25% prawn at a total density of 20 000 ha^?1 appeared to be the best stocking ratio in terms of fish production as well as economics for a periphyton‐based polyculture system.     

Comparative changes in water quality and role of pond soil after application of different levels of organic and inorganic inputs

Changes in water parameters were studied in a yard experiment for 7 weeks after application of cow dung at 20, 50 and 100 t ha^?1, poultry manure at 4, 10 and 20 t ha^?1, feed mixture (groundnut oil cake and rice bran at 1:1) at 10, 20 and 30 t ha^?1 and inorganic fertilizers at 100 kg urea+50 kg single super phosphate (SSP) ha^?1, twice this dose (2x ha^?1) and thrice this dose (3x ha^?1). To study the role of soil in the mineralization process, each treatment was divided into two groups – one with and the other without soil substrate. Higher degree of changes in water parameters was observed at higher input levels. Both organic amendment and inorganic fertilization caused significant reduction (P<0.05) in dissolved oxygen and increase in free CO₂, dissolved organic matter, total ammonia, nitrite, nitrate and phosphorus contents of water. Organic inputs significantly decreased (P<0.05) water pH and increased total alkalinity and hardness. In contrast, inorganic fertilization caused a significant increase in pH; alkalinity and hardness increased significantly in the presence of soil, but reduced in its absence. In organic input, presence of soil substrate caused significantly lower value of pH, dissolved oxygen, dissolved organic matter and phosphate‐phosphorus and significantly higher free CO₂, alkalinity, hardness, ammonia, nitrite and nitrate contents, compared with those in the absence of soil, revealing enhanced microbial mineralization in the presence of soil.     

The fate of chlortetracycline residues in a simulated chicken–fish integrated farming systems

Two experiments were conducted at the Asian Institute of Technology, Pathumthani, Thailand to investigate the fate of chlortetracycline (CTC) residue in chicken manure and its effect on integrated chicken–fish farming system. During the first experiment, broiler chickens were raised and CTC residues in their manure were analysed. Chicken fed diets containing 0, 50, 200 and 800 CTC mg kg^?1 had CTC residue levels of 0, 0.9, 3.8 and 6.5 CTC ng g^?1. Once the diet containing CTC was withdrawn, CTC in the manure dropped to negligible amounts (0, 0, 0.2 and 0.5 CTC ng g^?1) within 1 day. Integrated chicken–fish farming systems were simulated during the second experiment to determine the fate of antibiotic residues in chicken manure in aquaculture environment. Chickens were fed a CTC‐free diet and a feed containing CTC at 200 mg kg^?1. Ten 4 m³ square concrete tanks (2 × 2 × 1 m) were used for the experiment. Five tanks were fertilized with CTC‐contaminated manure and the remaining five tanks were fertilized with CTC‐free manure at a rate of 100 kg dry matter ha^?1 day^?1. Sex‐reversed Nile tilapia (Oreochromis niloticus) was stocked at 12 fish tank^?1 on the 14th day after chicken manure application. The immuno‐radio microbial receptor assay (Charm II test) revealed that edible fish muscle, fish intestinal tract and sediment were contaminated by CTC at rates of 7.21, 22.104 and 1.788 ng g^?1, respectively, after 45 days. Chlortetracycline was detected on day 20 in the water column and gradually increased from 0.26 to 12.13 ng g^?1. Chlortetracycline residues were not detected in fish or the aquatic environment of the CTC‐free treatment. The results demonstrate the potential for antibiotic residue accumulation in fish and aquatic environment when CTC‐contaminated chicken manure is used for pond fertilization.     

A partial economic analysis for Nile tilapia Oreochromis niloticus L. and sharptoothed catfish Clarias gariepinus (Burchell 1822) polyculture in central Kenya

Aquaculture development in Kenya has been hampered by lack of targeted feeds. Chemical fertilizers can enhance natural food production and thus indirectly provide protein to complement energy-rich cereal brans used as feed. Consequently, an experiment was conducted at Sagana Fish Farm in central Kenya to realize least-cost combinations of rice bran and fertilizer. Twelve 800 m² (0.08 ha) ponds were stocked with juvenile (32 g) Oreochromis niloticus L. at 2 m⁻² and Clarias gariepinus (Burchell 1822) (fingerlings of 4.6 g) at 0.2 m⁻². Four treatments, calculated to approximate isonitrogenous conditions, were applied in triplicate as follows: (1) urea and diammonium phosphate (DAP) to provide 16 kg of N ha⁻¹ week⁻¹ and 4 kg of P ha⁻¹ week⁻¹; (2) urea and DAP applied to give 8 kg of N ha⁻¹ week⁻¹ and 2 kg of P ha⁻¹ week⁻¹, plus rice bran fed at 60 kg ha⁻¹ day⁻¹; (3) rice bran fed at 120 kg ha⁻¹ day⁻¹; (4) rice bran as in treatment 3 and fertilizer as in treatment 2. Ponds were sampled monthly to measure fish growth, and drained completely after 20 weeks. A partial economic analysis indicated minimal net profits of K.Sh. 18 851 (US$ 251), K.Sh. 9895 (US$ 132), K.Sh. 3299 (US$ 44) and K.Sh. 7015 (US$ 94) for treatments 1–4, respectively, because of high feed and seed costs.     

Ingestion and utilization of periphyton grown on artificial substrates by Nile tilapia, Oreochromis niloticus L.

The study was carried out to quantify the periphyton biomass developed on glass substrates over time, to investigate the effects of periphyton quantity and fish size on the ingestion rate by fish, and to determine the feed conversion ratio (FCR) of periphyton by tilapia Oreochromis niloticus. Periphyton was grown in two fertilised 1000‐l tanks on glass slides and monitored as dry matter (g), ash‐free dry matter (g) and chlorophyll a concentrations (mg) per unit surface area (m²) over a six week period. Ingestion rate was determined for two sizes of tilapia (7 and 24 g) which were provided with four different periphyton densities. Determination of FCR was made after feeding three individual fish ad libitum with periphyton for two weeks. Periphyton ash‐free dry matter increased sharply during the first half of the trial with a peak being recorded at week 3 (75.5 g m^?2). Productivity was 2.4 g ash‐free dry matter m^?2 d^?1 during the first three weeks. Mean chlorophyll a concentration showed a cyclic pattern throughout the study with the lowest value being measured during the last week. Ingestion rates were 0.90 and 0.18 mg dry matter g fish body weight^?1 h^?1 for small and medium fish respectively. Ingestion rate among small fish increased significantly (P < 0.05) with periphyton density, but not for medium size fish. Although periphyton ash content was high (55% dry matter), fish growth was sustained. Fish harvested 70% of total periphyton dry matter that was offered to them. The FCR for periphyton was 2.81 on a dry matter basis and 1.34 on an ash‐free dry matter basis.     

Comparison of rice straw and bamboo stick substrates in periphyton-based carp polyculture systems

An experiment was conducted to compare rice straw mat and kanchi (bamboo sticks) as substrates in periphyton‐based polyculture systems. The experiment had three treatments: (a) no substrate (control), (b) rice straw as a substrate (3 × 2.7 kg pond^?1) and (c) kanchi as a substrate (390 kanchi pond^?1). Fingerlings (n=40) of rohu, Labeo rohita (24.5±0.5 g); mrigal, Cirrhinus mrigala (25.1±0.6 g); catla, Catla catla (25.8±0.5 g); common carp, Cyprinus carpio (27.6±0.6 g), and silver carp, Hypophthalmichthys molitrix (30.4±0.9 g) were stocked at a 3:2:2:2:1 ratio and cultured for 90 days. There were no differences in the number of plankton, periphyton and macro‐zoobenthos among the treatments. The total plate count of bacteria was higher in the rice straw treatment (41 320 million cfu m^?2) than that in the kanchi treatment (11 780 million cfu m^?2). Growth and the final mean weight of rohu, catla and common carp were higher in the substrate treatments than those in the control. Rice straw and kanchi treatment, respectively, resulted in 38% and 47% higher combined total weight gain over control. Gross margin analysis showed that rice straw treatment resulted in more profit than the control and kanchi treatment. Therefore, rice straw has the potential to be used to increase production in the low‐input rural aquaculture.     

C/N ratio control and substrate addition for periphyton development jointly enhance freshwater prawn Macrobrachium rosenbergii production in ponds

The present research investigated the effect of carbon/nitrogen ratio (C/N ratio) control in ponds with or without substrate addition for periphyton development on production of giant freshwater prawn. C/N ratios of 10, 15 and 20 were investigated in 40 m^− 2 ponds stocked with 2 prawn juveniles (5.023 ± 0.02 g) m^− 2 with or without added substrates for periphyton development. The various treatment combinations of C/N ratio and periphyton substrate addition are abbreviated as ‘CN10’, ‘CN15’, ‘CN20’, ‘CN10 + P’, ‘CN15 + P’ and ‘CN20 + P’, P representing periphyton substrate. A locally formulated and prepared feed containing 30% crude protein with C/N ratio10 was applied. Tapioca starch was used as carbohydrate source for manipulating C/N ratio and applied to the water column separately from the feed. Increasing the C/N ratio from 10 to 20 reduced (P < 0.001) the total ammonia-nitrogen (TAN), nitrite–nitrogen (NO₂–N) and nitrate–nitrogen (NO₃–N) in water column and total Kjeldahl nitrogen (TKN) in sediment. The addition of substrates only influenced the NO₂–N concentration in the water column (P < 0.001). Increasing the C/N ratio raised the total heterotrophic bacterial (THB) population in the water column, sediment and periphyton (P < 0.001). It also increased the dry matter (DM), ash free dry matter (AFDM), and chlorophyll a content of periphyton (P < 0.001). The lowest specific growth rate (SGR), the highest food conversion ratio (FCR), and the lowest protein efficiency ratio (PER) were recorded in treatment CN10 (P < 0.05). The addition of substrates did not influence size at harvest (P > 0.05) but improved the survival from 62.8 to 72% (P < 0.001). Increasing the C/N ratio from 10 to 20 increased the net yield by 40% and addition of substrate increased the net yield by 23%. The combination of C/N ratio control and substrate addition increased the net yield by 75% from 309 (CN10) to 540 (CN20 + P) kg ha^− 1 (120 days)^− 1. This 75% higher production concurred with (1) a lower inorganic nitrogen content in the water column, (2) a higher THB abundance supplying additional single cell protein to augment the prawn production, and (3) an improved periphyton productivity and quality.     

Autotrophic and heterotrophic production of micro-organisms in intensely-manured fish ponds,and related fish yields

Intensely-manured ponds produce 15–30 kg fish ha^?1 day^?1 with cow or chicken manure and nitrogen- and phosphate-rich fertilizers as the only nutritional inputs. The manure as it is supplied to the ponds is not a good fish food and does not produce good fish growth. Quantitative analysis shows that the production of all organisms, autotrophic and heterotrophic, pelagic and benthic, large enough to be used directly by the fish (i.e., larger than 37 microns) is adequate to account for less than half of the measured fish growth. Production within the microbial community that flourishes on and rapidly digests the manure organic matter is adequate to produce the measured fish growth. The fish appear to harvest the microorganisms at the level of bacteria and protozoa, by ingesting the small straw-like particles which comprise much of the manure and serve as the substrate for the microbial growth.     

The potential of periphyton-based culture of the native major carp calbaush, Labeo calbasu (Hamilton)

The project evaluated the effect of installing scrap bamboo (‘kanchi’) as a substrate for periphyton on growth and production of the indigenous major carp calbaush, Labeo calbasu (Hamilton). The impacts of fish grazing on the periphyton community were also assessed. Six ponds were used, three of which were provided with kanchi poles (700 per pond, spaced 30 cm apart). Ponds were limed and fertilized and stocked with L. calbasu fingerlings (mean total length = 5.16 cm; mean weight = 2.10 g) at a rate of 10 000 fingerlings ha^–1 (75 fish per pond). There were no statistically significant differences in water quality between treatments, although differences in phytoplankton community composition were observed. Zooplankton numbers were the same in both treatments. While there was clear evidence that periphyton was being exploited by the fish, Chlorophycae being most affected, grazing was insufficient to cause significant reductions in total periphyton densities. Fish survival and specific growth rates (SGRs) were significantly higher in ponds with substrates, production in treatments with and without scrap bamboo substrate being 712.90 and 399.11 kg ha^–1, respectively, over the 120-day period. However, production in both treatments was low in comparison with other studies, water temperatures (23.6–32.7 °C) being less than optimum for growth. It was concluded that kanchi and other locally available materials might be used to increase the production of some species of fish, although further evaluation of production economics is required.     

Effects of C/N ratio and periphyton substrates on pond ecology and production performance in giant freshwater prawn Macrobrachium rosenbergii (De Man, 1879) and tilapia Oreochromis niloticus (Linnaeus, 1758) polyculture system

The production performances of giant freshwater prawn Macrobrachium rosenbergii and Nile tilapia Oreochromis niloticus in C/N‐controlled periphyton‐based polyculture systems were evaluated in triplicate. Three different management practices were compared: the traditional practice without addition of periphyton substrates and carbohydrate (Control), addition of maize flour to maintain a carbon: nitrogen rate of 20:1 (treatment CN) and addition of both maize flour and periphyton substrates (treatment CN+P). This experiment used a pre‐optimized stocking density of tilapia and freshwater prawn by Asaduzzaman et al. Aquaculture [286 (2009) 72]. All ponds were stocked with prawn (3 m²) and monosex Nile tilapia (1 m^?2). Bamboo side shoots were posted vertically into the pond bottoms as periphyton substrate covering an additional area of 171 m² for periphyton development. A locally formulated and prepared feed containing 17% crude protein with C/N ratio close to 15:1 was applied twice daily in all ponds considering the body weight of freshwater prawn only. Water quality parameters, except total alkalinity did not vary significantly (P > 0.05) among treatments. Both, organic matter and total heterotrophic bacterial loads (THB) in the sediment were significantly (P < 0.05) higher in treatment CN+P followed by treatment CN and control. Periphyton biomass in terms of dry matter and chlorophyll a values constantly decreased during the culture period. Substrates contributed 66% and 102% higher net yield of freshwater prawn than CN and control treatment respectively.     

Production performance of sutchi catfish Pangasianodon hypophthalmus S. in restricted feeding regime: effects on gut,liver and meat quality

The experiment was carried out to evaluate the production performance of sutchi catfish, Pangasianodon hypophthalmus in restricted feeding regimes and their effects on gut and liver indices and body composition. Four feeding regimes were evaluated: fed to satiation twice per day (treatment daily feeding); 1‐day food deprivation and 1‐day feeding (treatment 1D‐1F), 2‐day deprivation and 2‐day feeding (treatment 2D‐2F) and 5‐day deprivation and 5‐day feeding (treatment 5D‐5F). Fingerlings (mean weight 37 ± 3 g, mean total length 18 ± 2 cm) were stocked in replicated earthen ponds at a density of 25 000 ha^?1 and cultured for 18 weeks during which commercial diet (33% crude protein) were delivered to apparent satiation on the feeding day according to the treatment. Results showed that the daily feeding and 1D‐1F treatments resulted in similar individual weight gain (515–536 g) and net fish production (10 954–11 387 kg ha^?1) as compared with treatment 2D‐2F (weight gain 309 g; net production 6700 kg ha^?1) or treatment 5D‐5F (weight gain 251 g; net production 5651 kg ha^?1). While fish body protein levels were not affected by food deprivation, lipid contents were lowest in treatments 2D‐2F and 5D‐5F. The study concluded that sutchi catfish could be cultured in alternate‐day feeding regime without any negative effects on production and meat quality of fish resulting in a net profit of USD 2750 ha^?1 pond.     

Pond farming of Nile tilapia, Oreochromis niloticus (L.), in northern Cameroon. Mixed culture of large tilapia (> 200 g) with cattle manure and cottonseed cake as pond inputs, and African catfish, Clarias gariepinus (Burchell), as police-fish

An experiment was conducted with tilapia-catfish polyculture at the Lagdo Fisheries Station in northern Cameroon. The objectives were: 1. To estimate the effect of supplementary cottonseed cake on net pond production in ponds already receiving dried cattle manure as basic treatment: and 2. To study the performance of African catfish, Clarias gariepinus (Burchell). in recruitment control of Nile tilapia, Oreochromis niloticus (L.). Recruitment control is essential in obtaining large tilapia sizes demanded in the market. Cottonseed cake, the most important agricultural by-product in the region, is expensive. Dried cattle manure may be collected free from corrals deserted by pastoral ethnic groups. Three treatments were tested in duplo in six earthen ponds of 525 m² each; treatment A. daily application of dried cattle manure only (266 kg ha^?1 day^?1); treatment B, daily manure + cottonseed at a nominal daily rate of 3% of tilapia biomass: treatment C, daily manure + cottonseed cake at 6% of tilapia biomass. Stocking densities per pond were 250 male Nile tilapia (mean W_o 222 g), 150 female tilapia (W₀= 202 g), 30 ‘large’ African catfish (W_o= 198 g); and 30 ‘small’ catfish (W₀= 52 g). Mean fish densities were 0.76 tilapia m^?2 and 0.11 catfish m^?2. Application of dried manure and cottonseed cake was 6 days per week, and the culture period was 100 days. Fish were sampled every month and feeding rates were adjusted accordingly. Dissolved oxygen content and algal turbidity (Secchi disc) were measured once a week. Extrapolated net pond productions, including recruits, were: -0.41 ha^?1 year^?1 (treatment A); 4.8 t ha^?1 year^?1 (treatment B) and 6.5 t ha^?1 year^?1 (treatment C). Differences between treatments B and C were not significant(P < 0.05). Fertilization with dried cattle manure only (zero cottonseed cake) led to a negative net pond production in treatment A (negative net tilapia production but slightly positive net catfish production). Dried manure at the given application rate did not contribute sufficient nutrients to maintain the stocked fish biomass via enhanced natural production, while pond biomass was high for such an extensive system (manure only). Best fish growth was observed in treatment C (male tilapia, 0.9 gday^?1: large catfish, 6.9 g day^?1) although differences between treatments B and C were not significant. Growth of male and female was not significantly different, but growth rates of tilapia and catfish were significantly different (P & lt; 0.05). Average yields of tilapia recruits in treatment B (1539 kg ha^?1 year^?1) and C (1829 kg ha^?1year^?1) were about four times the average yield of recruits in treatment A (468 kg ha^?1 year^?1) but differences between treatments A, B and C were not significant. It was sugcess, or the reproductive efficiency of tilapia in treatment A could have been lower as a result of that treatment. However, clouds of up-swimming fry appeared to be at least as numerous in the replicate ponds of treatment A as in the ponds of treatments B and C.     

Performance of common carp,Cyprinus carpio L. and Nile tilapia,Oreochromis niloticus (L.) in integrated rice–fish culture in Bangladesh

Irrigated rice fields have enormous potential for expanding the aquaculture production in rice producing countries. Two field experiments were carried out at the Bangladesh Agricultural University, Mymensingh, to optimize the productivity of integrated rice–fish systems using Nile tilapia, Oreochromis niloticus (L.), and common carp, Cyprinus carpio L. Both experiments were laid out in a randomized complete block design with three replicates per treatment and regular rice monoculture as control. In the first trial, carp and tilapia were tested in single culture and in mixed culture with supplementary feeding at 2× maintenance level. The highest fish yield was obtained in the carp/tilapia mixed culture (586 ± 125 kg ha^− 1), followed by tilapia alone (540 ± 65 kg ha^− 1), and carp alone (257 ± 95 kg ha^− 1). Carp had significantly lower yield than the other two fish groups (p < 0.05) due to high mortality and inefficient feed utilization. As the carp/tilapia combination performed the best in the first experiment, it was tested with different inputs in the second trial, i.e. regular urea fertilization and two different feeding levels. The feeding levels were: continuous feeding at 2× maintenance level (feed level I) and a declining feeding schedule from 4× to 2× maintenance level (feed level II). The highest fish yield was obtained in feed level II (935 ± 29 kg ha^− 1), followed by feed level I (776 ± 22 kg ha^− 1), and the non-fed group (515 ± 85 kg ha^− 1). Yield differences between the treatments were significant at p < 0.05. Rice yields showed controversial effects between the rice–fish treatments and were dependent on the inputs provided. The highest rice production (4.2 t ha^− 1) was obtained from rice–fish plots with regular urea fertilization. Various significant effects of fish on water quality parameters were observed. Fish decreased the dissolved oxygen (DO) and pH value compared to rice only, especially when supplementary feed was provided. Moreover, fish stimulated the growth of phytoplankton and increased chlorophyll-a concentration. In conclusion, carp/tilapia mixed culture with supplementary feeding was found to be optimal for maximizing the output from rice–fish culture.     

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.     

Contribution of microorganisms to the biofilm nutritional quality: protein and lipid contents

The nutritional quality of biofilm, a microbial community associated to an organic matrix, was evaluated in artificial substrate (polyethylene screen) in net cages during 30 days in the Patos Lagoon estuary, Southern Brazil. During this period, samples of biofilm were collected each 5 days for analysis of chlorophyll a, microorganisms abundance, dry weight, protein and lipid contents. During the study, chlorophyll a varied from 0.38 to 2.75 μg cm^?2; dry weight between 7.16 and 17.63 mg cm^?2; protein content from 0.43 to 1.76 mg cm^?2 and lipid concentration between 1.21 and 4.23 mg cm^?2. The variation of lipid in the biofilm was closely related to the abundance of free heterotrophic bacteria (34.25–56.54 × 10⁶ cells cm^?2), filamentous cyanobacteria (7.5–15.9 × 10⁶ filaments cm^?2), flagellates (6.92–12.89 × 10⁶ cells cm^?2) and mainly nematodes (29–1,414 organisms cm^?2), while protein content varied similarly to the abundance of unicellular centric diatoms (52.10–179.81 × 10³ cells cm^?2), and nematodes. This information will allow a better management of food supply to raised aquatic organism with the utilization of natural productivity in the culture systems, with considerable decrease in production costs.     

Effect of dietary supplementation of periphyton on growth,immune response and metabolic enzyme activities in Penaeus monodon

A 60‐day indoor trial was conducted to study the effect of periphyton supplementation on metabolic and immune responses in tiger shrimp, Penaeus monodon. Periphyton developed over bamboo substrate in outdoor tanks (15 m²) was used as dietary supplement for P. monodon (2.02 ± 0.04 g) reared in 1000 L FRP tanks. Graded levels of periphyton were included in shrimp basal diets: 0% (P0), 3% (P3), 6% (P6), 9% (P9) and P0 diet with natural periphyton (NP) over bamboo substrate. At the end of the trial, P6 and NP showed significantly higher (P < 0.01) growth rate, 23.9% and 20%, respectively, compared with control, P0. Comparatively, lower level of metabolic enzymes, such as lactate dehydrogenase, malate dehydrogenase, aspartate aminotransferase and alanine aminotransferase, was recorded in treatments P3, P6 and NP compared with control, P0. The periphyton‐supplemented group, P3 had significantly higher (P < 0.05) superoxide dismutase (15.83 ± 0.96) and catalase activity (15.73 ± 0.69) compared to 6.88 ± 2.84 and 9.15 ± 0.67 unit mg^?1 protein min^?1_, respectively, in P0. Similarly, higher total haemocyte counts, 32.58 ± 1.30, 28.51 ± 3.12 and 27.26 ± 4.43 × 10⁶ cells mL^?1_, were recorded in P6, NP and P3, respectively, compared to P0, 23.57 ± 1.80 × 10⁶ cells mL^?1. After challenge with Vibrio harveyi, P3 recorded the highest relative percentage survival 67% followed by NP (58%) and P6 (42%) compared with control. However, treatment with highest periphyton inclusion (P9) did not differ significantly with P0 on growth and immunological parameters. This study indicates that periphyton supplementation at 3–6% level improves growth, immune response and metabolic activities in P. monodon.     

Effect of fertilization frequency on pond productivity and fish biomass in still water ponds stocked with Cirrhinus mrigala (Ham.)

Four different fertilization frequencies, namely twice per week, once per week, twice a month and once a month, were used in ponds to assess their effects on nutrient release, pond productivity and fish biomass. All ponds received the same total fertilizer inputs during the experimental period of 60 days (cow dung 208.3 kg ha^?1 week^?1, TSP 9.8 kg ha^?1 week^?1, urea 6.0 kg ha^?1 week^?1). Studies have revealed that the highest values of fish biomass, specific growth rate (SGR), net primary productivity (NPP), plankton population and nutrients were observed in the ponds that were fertilized twice a month. A strong and significant correlation of fertilization frequency was observed with dissolved oxygen, biochemical oxygen demand (BOD), alkalinity, nutrient release, NPP, plankton density (no. L^?1), fish biomass and SGR. The linear relationship between NPP and fish biomass/SGR for all the ponds was strong (r²= 0.88). Sediment chemistry revealed that O‐PO₄, NO₃‐N, organic carbon and electrical conductivity (EC) increased significantly (P<0.05) with a decrease in the frequency of fertilization, while alkalinity and calcium were high in ponds that were fertilized twice a month.