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.     

The potential of periphyton-based culture of two Indian major carps, rohu Labeo rohita (Hamilton) and gonia Labeo gonius (Linnaeus)

The effects of periphyton, grown on bamboo substrates, on growth and production of two Indian major carps, rohu, Labeo rohita (Hamilton) and gonia, Labeo gonius (Linnaeus), were studied at the Bangladesh Agricultural University, Mymensingh. For each species, five ponds were provided with bamboo substrates and five ponds without substrate (control). Ponds were stocked at a rate of 10 000 ha^?1 in both treatments. There was no discernible difference in water quality parameters between treatments. A large number of plankton (39 genera) showed periphytic nature and colonized the bamboo substrates. Rohu grew faster, resulting in a 77% higher net production (P < 0.05) in the ponds with bamboo substrates compared with the ponds without substrate. In contrast, the growth and production of gonia did not vary significantly (P > 0.05) between the substrate and control ponds. Rohu seems to be a more suitable candidate for periphyton‐based aquaculture systems than gonia.     

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%).     

Phosphorus Budget in Integrated Multitrophic Aquaculture Systems with Nile Tilapia,Oreochromis niloticus,and Amazon River Prawn,Macrobrachium amazonicum

Integrated multitrophic aquaculture (IMTA) systems are designed mainly for efficient use of resources. Substrates added to aquaculture ponds provide space for periphyton to settle and recover nutrients, making these nutrients available to the species being reared. The present study is centered on the phosphorus budget, analyzing the main ecological compartments of IMTA systems in earthen ponds stocked with Amazon River prawn, Macrobrachium amazonicum, and Nile tilapia, Oreochromis niloticus, with or without different added substrates. The experimental design was completely randomized, with three treatments (without a substrate, with a geotextile fabric substrate, and with a bamboo substrate) and four replications. Phosphorus entered the systems mainly in tilapia feed (ca. 50–61%), inlet water (ca. 17–27%), and fertilizer (ca. 6–7%). Input of phosphorus from other compartments ranged from 1.5 to 1.9%. Most phosphorus was accumulated at the pond bottom as sediment (ca. 60–68%) and fish biomass (ca. 18–26%), or discharged in the outlet water (ca. 7–10%). Feeding is the main driver for the distribution of phosphorus in the ponds. Levels of phosphorus retained in reared animals (20–28%) were higher in these IMTA systems than in tilapia and prawn monocultures (reported as 10–20% and 10–13%, respectively). Nonetheless, the present data showed that the addition of different types of substrates might not improve the recovery of phosphorus in animal biomass as initially supposed. Even so, these IMTA systems decreased the amount of phosphorus released in effluents, and this decrease was enhanced by the addition of substrates, reducing the impact on the receiving waterbodies.     

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.     

Culture of organic tilapia to market size in periphyton‐based ponds with reduced feed inputs

In fish production under organic standards, only organic feeds and manures can be supplied. The cost of organic pelleted feeds is twice that of regular feeds. To support the organic production of hybrid tilapia [Oreochromis niloticus (L.) ×Oreochromis aureus (Steindachner)], a series of experiments in earthen ponds, to improve natural food production for this fish while reducing costs of added feed, are in progress. To improve natural food production for tilapia, plastic substrates equivalent to 50% of the pond surface were introduced into the water column to induce periphyton growth on them. To reduce costs, the feeding rate on pelleted feed was reduced to 60%. Tilapia growth in these periphyton ponds was then compared with ponds without underwater substrates that received the full feed rate. The polyculture consisted of 90% large (320 g stocking weight) hybrid tilapia and small amounts of other fish, at a total stocking density of 13 800 fish ha^?1, during 87 summer days. The results showed improved nitrification and the development of a large autotrophic periphyton biomass that competed with the phytoplankton in the periphyton ponds, and only a 10% and 15% reduction, respectively, in the tilapia daily and specific growth rates, with 40% feed saving. These results point towards periphyton‐based aquaculture as an appropriate technology for the reduction in production costs, allowing economically viable organic tilapia production.     

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.     

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.     

The effects of periphyton substrate and fish stocking density on water quality, phytoplankton, periphyton and fish growth

The objectives of this study were to determine how periphyton and phytoplankton biomass vary with grazing pressure by tilapia Oreochromis niloticus, to evaluate the growth performance of fish when substrate is introduced and to calculate the efficiency of nitrogen utilization in substrate and non‐substrate systems. Ten circular 1000‐L plastic tanks were filled with 15 cm of loamy soil bottom and water. Five different treatments were applied: eight tilapias with substrate (treatment 8T/S), eight tilapias without substrate (treatment 8T), four tilapias with substrate (treatment 4T/S), four tilapias without substrate (treatment 4T) and no tilapia with substrate (treatment 0T/S). Each week, 2 g of NaNO₃ and 3.5 g of single superphosphate (SSP) were applied to each tank. Sixteen glass slides (1 m×4 cm×4 mm) were installed vertically in the tank bottom, one portion extending above the water surface and equally spaced within the water column in all substrate tanks. Periphyton and phytoplankton quantity and quality, water quality, fish growth and proximate fish composition were measured. Because of grazing, phytoplankton and periphyton biomass decreased after the introduction of fish to the tanks. The periphyton biomass was higher in non‐fish tanks (treatment 0T/S) throughout the experiment than that in tanks with fish (treatments 8T/S and 4T/S). The periphyton biomass was similar in the 4T/S and 8T/S treatments, suggesting that the grazing pressure on periphyton biomass reached threshold levels. Fish ate 25–36% of the total standing biomass every day. Tilapia growth was significantly higher in treatments with substrate. Nitrogen retention was double in substrate ponds compared with in control ponds. There were no significant effects of periphyton substrate or fish density on body composition of fish.     

Evaluation of Four Biodegradable Substrates for Periphyton and Fish Production

Four locally available biodegradable substrates—sugarcane (Saccharum officinales) bagasse, palm (Borasus flabellifera) leaf, coconut (Cocos nucifera) leaf, and bamboo (Bambusa bambos) mat—were evaluated for the production of periphyton and a polyculture of rohu (Labeo rohita) and common carp (Cyprinus carpio) in poultry-manured ponds. Chlorophyll-a, phaeophytin-a, and total pigment content of periphyton were not significantly different (P > 0.05) among substrate types. Dry matter and ash-free dry matter of coconut leaf periphyton were significantly higher (P < 0.05) than that of the other substrates. All four substrates induced significantly (P < 0.05) higher growth, production, and survival of rohu and common carp. Among the substrates used, coconut leaf was more effective in enhancing fish production.     

Potential of nutrient reutilisation in combined intensive–extensive pond systems

The experiments on the intensive–extensive system were carried out between 2008 and 2010 in three ponds (area 310 m², depth 1 m) serving as extensive units, where cages were placed as an intensive units (volume 10 m³) one in each pond. In the intensive units, African catfish (Clarias gariepinus) was cultured and fed with pellet whilst common carp (Cyprinus carpio) was stocked in each extensive unit and raised without any artificial feeding. Three different setups of extensive ponds were tested: the additional artificial plastic substrate for periphyton development equalled to 0, 100 and 200 % of the pond surface area (PP0 %, PP100 % and PP200 %) at feed loading level of 1.2, 1.9 and 2.8 gN m^?2 day^?1 in 2008, 2009 and 2010, respectively. The additional net fish yields in the extensive unit were 2.8–6.5 t ha^?1 in PP0 %, 5.1–8.1 t ha^?1 in PP100 % and 2.1–4.3 t ha^?1 in PP200 %. The nitrogen recovery in the additional fish yields of extensive ponds, expressed as the percentage of feed load, was 5.6–6.1, 6.8–10 and 2.1–6.1 % in the treatments PP0 %, PP100 % and PP200 %, respectively. The combined fish production resulted in higher protein utilisation by 22–26 %; even this ratio can be increased by 33–45 % with periphyton application.     

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.     

The effects of perch, Perca fluviatilis L., and bronze bream, Abramis brama (L.), on insect emergence and benthic invertebrate abundance in experimental ponds

Abstract The effects of perch, Perca fluviatilis L., and bronze bream, Abramis brama (L.), predation on the production of insects emerging at the water surface and the autumn biomass of benthic macro-invertebrates were assessed in a series of experimental ponds. The study attempted to discover whether fish affect food availability for diving and dabbling ducks in freshwater habitats. Ten ponds (bisected by fine netting) were used for the study: one was left totally fish-free, whilst one half of each of three groups of three ponds was stocked with either perch, bream or perch plus bream. The relative abundance of emerging insects (mainly Chironomidae) was significantly reduced in two perch ponds, two perch + bream ponds and two bream ponds. The autumn standing crops of benthic macroinvertebrates were significantly reduced in one perch pond, three bream ponds and one perch plus bream pond. These results support findings of a contemporaneous large bio-manipulation experiment carried out in two adjacent lakes. During the biomanipulation studies, aquatic invertebrate standing stocks greatly increased after the removal of fish and decreased following restocking.     

Impact of Substrate Physical Characteristics on Grow Out of Freshwater Prawn, Macrobrachium rosenbergii, in Ponds and Pond Microcosm Tanks

Two independent trials were conducted to evaluate the effects of different physical characteristics of substrate materials on growth and survival of freshwater prawn. In Trial 1, juvenile prawns (0.4 ± 0.2 g) were stocked at 123 prawns/m² of tank bottom into twenty‐one 18,000‐L fiberglass tanks managed as pond microcosms. Six substrate materials were chosen to allow comparisons of surface area, mesh size, color, and texture. A control treatment received no added substrate. There were three replicate tanks per treatment. Substrates were positioned vertically at a rate sufficient to increase the bottom surface area by 100%. Prawns were fed a 32% protein sinking diet according to a feed chart. After 110 d, there was no significant difference (P > 0.05) in survival among treatments, averaging 72.6% overall. Prawns in the control treatment (no substrate) had significantly lower (P ≤ 0.05) average weights (9.5 g), lower production (1342 kg/ha), and higher feed conversion ratio (FCR; 2.5) than those in substrate treatments, which were not significantly different (P > 0.05) and averaged 13.4 g, 2404 kg/ha, and 1.3, respectively. For Trial 2, the least expensive substrate material from Trial 1 (lightweight polyethylene bird netting) was compared with the substrate most commonly used in commercial production (heavyweight orange polyethylene safety fencing) under practical pond conditions. Juvenile prawns (0.8 ± 0.3 g) were stocked at 61,600/ha into six 0.04‐ha earthen ponds. Each was randomly assigned one of the two substrate materials, and there were three replications per treatment. After 101 d, there were no significant differences (P > 0.05) between treatments in terms of survival (91%), average weight (34 g), total production (2150 kg/ha), or FCR (3.1). In these studies, physical characteristics of the substrate materials had little impact. The lightweight netting represents a 68% cost savings compared to the currently recommended substrate material.     

Forage-Based Feeding in Commercial Red Claw Ponds in Ecuador

Abstract

Red claw crayfish, Cherax quadricarinatus, are perhaps the first tropical species of crayfish to be cultured commercially. Culture traits and high market value could allow semi-intensive culture. Feeding strategies used in extensive crayfish ponds in temperate climates may not be the most appropriate for semi-intensive culture systems where year-round growth is possible. The following study was conducted to evaluate differences between using a pellet-based system versus a pellet-plus-forage-based system. The study was conducted in 14 0.3-ha ponds on a commercial farm in Ecuador. Juvenile red claw (1-2 g) were stocked into all ponds at a rate of 4/m². All ponds received pelleted shrimp rations at a rate of 3% per day. Seven ponds also received dried hay at a rate of 100 kg/ha/mo during the 3-month study. At harvest, red claw weights were similar (30-34 g), but survivals were significantly higher in ponds receiving pellets and hay (65%) than in ponds receiving pellets only (50%). Yields in pellet-fed ponds averaged 594 kg/ha, while red claw receiving pellets plus forage averaged 889 kg/ha. The addition of dried forage was thought to provide a larger variety of natural food organisms throughout a greater area of the pond bottom and provided additional substrate for dispersal and hiding. Addition of grasses from outside the pond is recommended over production of grasses grown within the pond.     

The impact of carp pond management upon macrozoobenthos assemblages in recipient pond canals

Impact of carp pond management upon macrozoobenthos assemblages was studied in inlet and outlet carp pond canals in South Moravia (Czech Republic). Four ponds (two eutrophic and two hypertrophic ones) with different types of fish farming management and intensification measures were selected for the evaluation of the impact of inlet water quality, discharge rate and pond stocking management upon the outlet water quality determinants based on macrozoobenthos evaluation during April–September 2009. Five inlet and four outlet canals were sampled by “kick–sampling” approach and also by using the artificial substrates. The pattern of water quality changes after the flow through the pond was predominantly influenced by inlet water quality. In ponds supplied with worsened inflow water quality with the saprobic index (SI) according to macrozoobenthos corresponding to alpha-mesosaprobity (SI 2.82–2.89), the outflow water quality was significantly improved by approximately half of the saprobic degree on SI 2.38–2.42. On the contrary, the inflow water quality corresponding to beta-mesosaprobity (SI, 2.32) was significantly (p < 0.01) deteriorated to alpha-mesosaprobity in the pond outflow. Macrozoobenthos diversity and the number of taxa reflected the flow through the pond identically with saprobic determinants. In ponds with poor inflow water quality, the number of macrozoobenthos taxa and its diversity increased in the outlet canals, and vice versa, in ponds with good-quality inflow water, the number of taxa and macrozoobenthos diversity decreased in outlet canals.     

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%).     

Nutrient budget of a marine fish pond in Eilat,Israel

Monthly budgets for nitrogen and phosphorus for a marine fish pond in Eilat were determined for the period September 1983 to June 1984. The ponds are operated as a semi-open system, 41% of the pond water being replaced each day by water from a nearby seawater well. Only 29% of the phosphorus and 36% of the nitrogen are incorporated into harvestable fish flesh (Sparus aurata or Mugil sp.). The remainder reaches the pond as uneaten food, fish faeces or excreted matter, and it is then available to support high levels of phytoplankton and heterotrophic activity. The total input of nutrients supplied to the ponds showed a seasonal trend, with the lowest amount being supplied at the beginning of the sampling period (October) (5.2 moles N/day, 0.25 moles P/day), and increasing in June to 10.6 moles N/day, 0.57 moles P/day. All the increase was due to the amount of food fed. A large proportion (70–80%) of the excess nutrients was exported from the system as dissolved or particulate matter in the overflow. Because of this the water quality of the ponds has remained at levels which have enabled 6.5–12 tons fish/ha to be cultured without regular drying of the ponds. Oysters have been grown on the plankton carried out with the overflow. The ponds have a surplus of nutrient inflow in October/November (1.9 moles N/day, 0.06 moles P/day), a small deficit of N (0.4 moles/day), and surplus of P (0.01 moles/day) in spring, and a large surplus again in May and June of 1.3 moles N/day, 0.11 moles P/day. In all, 60–120% of the nutrient inputs are directly accounted for.     

Effects of Two Densities of Caged Monosex Nile Tilapia, Oreochromis niloticus, on Water Quality, Phytoplankton Populations, and Production When Polycultured with Macrobrachium rosenbergii in Temperate Ponds

The effects of different densities of caged Nile tilapia, Oreochromis niloticus, on water quality, phytoplankton populations, prawn, and total pond production were evaluated in freshwater prawn, Macrobrachium rosenbergii, production ponds. The experiment consisted of three treatments with three 0.04‐ha replicates each. All ponds were stocked with graded, nursed juvenile prawn (0.9 ± 0.6 g) at 69,000/ha. Control (CTL) ponds contained only prawns. Low‐density polyculture (LDP) ponds also contained two cages (1 m³; 100 fish/cage) of monosex male tilapia (115.6 ± 22 g), and high‐density polyculture (HDP) ponds had four cages. Total culture period was 106 d for tilapia and 114 d for prawn. Overall mean afternoon pH level was significantly lower (P ≤ 0.05) in polyculture ponds than in CTL ponds but did not differ (P > 0.05) between LDP and HDP. Phytoplankton biovolume was reduced in polyculture treatments. Tilapia in the LDP treatment had significantly higher (P ≤ 0.05) harvest weights than in the HDP treatment. Prawn weights were higher (P ≤ 0.05) in polyculture than prawn monoculture. These data indicate that a caged tilapia/freshwater prawn polyculture system may provide pH control while maximizing pond resources in temperate areas.     

不同鱼类和采样时间的养殖池塘环境微生物群落研究

微生物群落是养殖池塘生态系统重要的组成部分。本研究在不同月份采集尼罗罗非鱼和斑点叉尾鮰池塘水体样品,分析水样中的硝酸盐氮、亚硝酸盐氮、氨氮、总氮和总磷等理化指标,利用Biolog-Eco微平板技术分析水体中微生物对各类碳源代谢的平均颜色变化率,利用高通量测序技术分析水体中的菌群结构,以期了解养殖鱼种类和季节对养殖池塘环境及菌群结构的影响。结果表明：冬季淡水养殖池塘水质和菌群结构不同于其他季节,养殖鱼类种类对池塘水体理化指标和水体微生物菌群结构的影响不大。不同采样时间的池塘水体理化指标差异显著,同一采样时间不同养殖鱼类池塘水体理化指标之间无显著差异。其中,1月尼罗罗非鱼养殖池塘水样中的NH4-N含量高于其他月份,显著高于4月和7月的水样(P<0.05)；1月TP含量显著高于1月、4月和7月(P<0.05)。1月斑点叉尾鮰养殖池塘水样中的TP和NO₃-N含量显著高于其他三个月份(P<0.05)。Biolog-ECO微平板技术检测到尼罗罗非鱼和斑点叉尾鮰养殖池塘水样中的微生物群落对碳水化合物和氨基酸的利用能力较强,对酚胺类化合物的利用能力较弱,4月斑点叉尾鮰养殖池塘水体微生物对碳源的利用率高于尼罗罗非鱼养殖池塘。高通量测序结果发现厚壁菌门(Firmicutes)和拟杆菌门(Bacteroidetes)是尼罗罗非鱼和斑点叉尾鮰养殖池塘水体中的绝对优势菌门。hgcI clade、CL500-29 marine group和C39等参与氮磷循环的菌属为淡水池塘养殖水体中的主要菌属。本研究结果为了解淡水养殖环境中微生物群落结构与变化规律、更有针对性的构建淡水养殖池塘尾水生态化处理方法提供科学依据。