Effects of stocking density, periphyton substrate and supplemental feed on biological processes affecting water quality in earthen tilapia-prawn polyculture ponds

The technical and economic potentials of tilapia, Oreochromis niloticus (L.), and giant river prawn, Macrobrachium rosenbergii (de Man), polyculture in periphyton-based systems are under investigation in an extensive research programme. This article is a combined analysis of data from four experiments exploring the effects of periphyton, fish, prawn and feed on water quality. Factor analysis and ancova models applied to the combined dataset allowed to identify the underlying ecological processes governing the system, and construct conceptual graphic models of the periphyton¿environment relationships observed. With the first factor, variability in water quality was due to autotrophic (photosynthesis and nutrient uptake) and heterotrophic (respiration and decomposition) processes affecting water quality in opposite directions. With the second factor, variability was related to decomposition on the bottom and nutrient release into the water column, algae production and sedimentation. The analysis of the relationships between both factors and the growth rates of tilapia and prawn in the different systems allowed a better understanding of the functioning of tilapia¿prawn ponds, and indicates that their joint culture is technically feasible and economically viable. Therefore, this technology is recommended for poverty alleviation and nutritional security in rural Bangladesh as well as in other countries of the region

Evaluation of production performance and profitability of hybrid red tilapia and genetically improved farmed tilapia (GIFT) strains in the carbon/nitrogen controlled periphyton-based (C/N- CP) on-farm prawn culture system in Bangladesh

Performance of hybrid red tilapia (Mutant, Oreochromis niloticus × Oreochromis mossambicus) and GIFT tilapia strain (Oreochromis niloticus) in C/N-CP prawn (Macrobrachium rosenbergii) farming system was evaluated at the farmers' pond at Bailor union under Trishal upazilla of Mymensingh district, Bangladesh. The on-farm trial had two treatments: TR and TG (named according to the tilapia strains) with three replications. Six rectangular ponds of varying sizes (400–880 m2) were used for this experiment. Hybrid red and GIFT tilapia stains were stocked with prawn at the stocking densities of 1 tilapia fingerlings (either red or GIFT strain) and 3 prawn juveniles m-2 in both treatments. Bamboo side shoot were posted vertically as periphyton substrate. This resulted in an additional substrate surface area of 1067 m2 for periphyton development equaling 147% of the pond surface area. Considering the body weight of freshwater prawn only, feeding rates were 10% of body weight at the beginning of the study (up to 30 days), and feeding application was gradually reduced to 3% in the last month assuming 80% survival. The abundance of total benthos and periphyton as well as total periphytic biomass were significantly higher (P < 0.05) in TR than TG treatment and they were also differed significantly (P < 0.05) among different months with a decreasing trends (exception to some extent) over the experimental period. The individual harvesting weight, individual weight gain, specific growth rate, Food Conversion Ratio (FCR), survival (%), gross and net yields of prawn were similar in two treatments. In contrast, the GIFT tilapia strain showed a higher (P < 0.05) individual harvesting weight, individual weight gain, specific growth rate ((SGR, % bw d-1), survival, gross and net yields (1935 and 1825 kg ha-1, respectively) combined gross and net yields (2952 and 2784 kg ha-1, respectively), and economic return (3755 US$ with BCR 0.82) than the hybrid Red tilapia

Periphyton-based pond polyculture system: a bioeconomic comparison of on-farm and on-station trials

A bioeconomic study of periphyton-based aquaculture in Bangladesh was carried out through comparison of on-farm and on-station trials. Five treatments, three on-farm and two on-station, each with four replications, were tried in a completely randomized design: on-farm control without substrate or feed (control), on-farm bamboo substrate only (treatment B-farm), on-farm substrate plus feed (BF-farm), on-station substrate only (B-station) and on-station substrate plus feed (BF-station). All ponds were stocked with three native major carps, rohu (Labeo rohita), catla (Catla catla) and mrigal (Cirrhinus mrigala) at a ratio of 60:40:15 and a stocking density of 11,500 juveniles ha&minus;1. All ponds were fertilized fortnightly with urea and triple super phosphate (TSP) at the same rate of 50 kg ha&minus;1. In substrate treatments, ponds were provided with bamboo poles as periphyton substrates. In fed treatments, rice bran and mustard oil cake (ratio 2:1 by weight) were applied. The environmental conditions of on-station ponds were better than on-farm ponds. Under on-farm condition, substrate plus feed (BF-farm) and substrate only (B-farm), respectively, resulted in 59% and 28% higher production over control. Under on-station condition, supplemental feed did not contribute significantly to the total fish production. However, on-station trial resulted in 77% higher combined net yield than on-farm trial. The cost&ndash;benefit analysis indicated that well-managed periphyton-based aquaculture practices might be a profitable business. The sustainability issues of this novel technology needs to be carefully assessed during the design and planning of aquacultural developmental efforts

Effects of C/N ratio and substrate addition on natural food communities in freshwater prawn monoculture ponds

An on-station trial was conducted to investigate the effects of three C/N ratios (10/1, 15/1 and 20/1) along with substrate presence or absence on natural food communities in freshwater prawn culture ponds. An experiment was carried out in 40 m2 ponds stocked with a stocking density of 2 prawn juveniles (5.023 ± 0.02 g)m−2. A locally formulated and prepared feed containing 30% crude protein with C/N ratio 10 was applied to all ponds. In order to raise the C/N ratio of the feed input to 15 and 20, tapioca starch was applied separately as a source of carbohydrate in addition to the artificial feed. Under substrate treatments, bamboo side shoots were posted vertically in pond bottoms resulting in 100% additional surface area as periphyton substrates. The treatments with different C/N ratios are referred to as “CN10”, “CN15” and “CN20”. Increasing the C/N ratio from 10 to 20 significantly increased the biovolume of phytoplankton, crustaceans and rotifers in the water column by 15%, 6% and 11%, respectively. The biovolume of periphyton was 50% higher in treatment CN20 compared to treatment CN10. Increasing the C/N ratio from 10 to 20 raised the biovolume of total heterotrophic bacteria(THB) in the water column (70%), sediment (36%) and periphyton (40%). The chironomids biovolume was also significantly higher (28%) in treatment CN20 compared to treatment CN10. The addition of substrates decreased the biovolume of water column plankton by 14% but the combined biovolume (plankton+periphyton) was almost double in substrate-added ponds. The biovolume of plankton, periphyton and THB increased significantly with culture time duration whereas the biovolume of benthic macroinvertebrates decreased significantly with culture time indicating that freshwater prawn grazed on them. A significant interaction between C/N ratios and substrate presence or absence was only observed for plankton biovolume in the water column. This study demonstrated that plankton, periphyton and microbial biofloc communities were under-utilized by the freshwater prawn in treatment CN20. This leaves room for increasing the stocking density of prawn and/or inclusion of periphyton grazing fish species to improve nutrient utilization efficiency and overall sustainability

Evaluation of polyculture of Indian major carps in periphyton-based ponds

Production of three Indian major carps, catla Catla catla, rohu Labeo rohita and kalbaush L. calbasu, in a periphyton-based polyculture system was compared. Bamboo poles, approximating a submerged surface area equal to the total pond surface area, were used as substrates for periphyton and were planted vertically into the pond bottom. Ponds were fertilized fortnightly with 4500 kg cow manure, 150 kg urea and 150 kg triple super phosphate (TSP) per hectare. Four stocking combinations were applied: 60% rohu plus 40% catla with a total stocking density of 10000 ha-1 (treatment CR), CR plus 15% kalbaush (C15), CR plus 30% kalbaush (C30) and CR plus 45% kalbaush (C45). A treatment with 60% rohu plus 40% catla without bamboo substrate was used as control (CR0). Treatments differed significantly in some water quality parameters (Secchi depth, total alkalinity, orthophosphate, total ammonia and chlorophyll a) and periphyton biomass (dry matter (DM), ash-free dry matter (AFDM) and ash content). The ash (15–19%), protein (23–26%) and energy (19–20 kJ g -1) contents of the estimated periphyton can be considered as broadly appropriate to fish dietary needs. The relative contributions of algae to the periphytic biomass were 30–60% depending on the treatment. In total, 50 genera of algae, 13 genera of zooplankton and some macrobenthic invertebrates were identified from the periphyton samples. Survival of rohu and catla was higher in ponds with bamboo poles than in the controls. Net fish yields of the three species were found to be higher in treatment C15. Highest total fish yield, over a 90-day culture period, was recorded in treatment C15 (2306 kg ha-1) followed by treatment C45 (1914 kg ha-1), treatment CR (1652 kg ha-1), treatment C30 (1507 kg ha-1) and treatment CR0 (577 kg ha-1). Fish production from the periphyton-based system was 2.8 times higher than that of the control. The addition of 15% kalbaush (i.e. a stocking ratio of 12:8:3 rohu–catla–kalbaush) at a total stocking density of 11500 juveniles ha-1 resulted in a further 40% increase in production and is an appropriate combination in a periphyton-based polyculture system. The stable nitrogen and carbon isotopes ratio indicated that rohu grazed on periphyton, whereas catla depended on planktonic food organisms

The effects of artificial substrates on freshwater pond productivity and water quality and the implications for periphyton-based aquaculture

As a first step in assessing the viability of periphyton-based fish production in South Asian pond aquaculture systems, the effects of artificial substrates on development of periphyton and on water quality were evaluated. Earthen ponds (10 × 7.5 m) were provided with an artificial substrate constructed from poles of either bamboo, kanchi or hizol tree branches (1.0 m2 artificial substrate per m2 pond surface). Higher periphyton biomass, in terms of dry matter (DM) (4.9 mg cm–2) and chlorophyll a (11.5 μg cm–2) developed on hizol and bamboo, respectively. Periphyton ash content was higher on hizol (41%) than on the other two substrate types (29%). Protein content of the periphyton growing on bamboo (38% of ash-free dry matter (AFDM)) was 50% higher than that on the other two substrate types. Maximum periphyton productivities of 1.01, 1.38 and 1.03 g C m–2 d–1 were obtained for bamboo, hizol and kanchi substrates, respectively. Taxonomic composition of periphyton showed a rapid development of a relatively stable community with few differences between the substrate types. In total, 56 genera of algal periphyton and 35 genera of phytoplankton were identified. Based on a periphyton productivity estimate of 2.2–2.8 g AFDM m–2 d–1, periphyton alone can sustain an estimated fish production of 5000 kg ha–1 year–1 through the addition of a substrate area equivalent to 100% of the pond surface area