M.A. Wahab

A comparison of fertilization, feeding and three periphyton substrates for increasing fish production in freshwater pond aquaculture in Bangladesh

Abstract A polyculture trial was conducted in earthen ponds in Bangladesh to compare traditional aquaculture techniques (fertilization only or fertilization plus feeding) with a combination of the same techniques and periphyton substrates. Three substrates (bamboo, jutestick and bamboo side shoot) were tested. Rohu ( Labeo rohita ), catla ( Catla catla ) and kalbaush ( L. calbasu ) were stocked at a 60:40:15 stocking ratio and at a total stocking density of 11,500 per hectare in 15 earthen ponds with five treatments: standard fertilization as input (Control), control plus supplemental feeding with rice bran and oil cake (Feed), control plus bamboo substrate (Bamboo), control plus jutestick substrate (Jutestick) and control plus bamboo side shoot substrate (Kanchi). Water quality, plankton and periphyton were monitored throughout the experiment. Significantly higher ammonia concentrations were recorded in Control and Feed treatments. The chlorophyll a concentration of pond water was significantly higher in the Feed treatment than in the Jutestick treatment. Dry matter content and mean abundance of the periphyton communities were higher in the first and the last month of the experiment without significant difference among the three substrate types. Periphyton chlorophyll a concentrations per unit surface area did not vary significantly among different substrate types but increased throughout the experimental period and decreased with increasing water depth. Specific growth rates of rohu and catla were higher in Substrate and Feed treatments than in the Control treatment. Combined net yields of fish in Control, Feed, Bamboo, Jutestick and Kanchi treatments were 1226, 1960, 2098, 2048 and 2032 kg ha −1 135 day −1 , respectively. Production in substrate systems was significantly higher (ANOVA, P

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 m 2 artificial substrate per m 2 pond surface). Higher periphyton biomass, in terms of dry matter (DM) (4.9 mg cm ‐2 ) and chlorophyll a (11.5 µ gc m ‐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.

Periphyton–water quality relationships in fertilized fishponds with artificial substrates

Abstract The potential of periphyton-based aquaculture in southern Asia is under investigation in an extensive research program. This paper is a further analysis of data from two experiments carried out in that framework, to explore periphyton–environment relationships in the absence of fish grazing pressure. Factor analysis and ANOVA models applied to data matrices of water quality, plankton and periphyton parameters allowed identifying the underlying ecological processes governing this novel periphyton-based pond system. The system was dominated by changes in time, and the main sources of variability were periphyton biomass increase through the culture period and its effect on water turbidity, processes affecting pond oxygenation and processes leading to surface–depth differences in water quality. All those processes act at the same time but with different intensities and time patterns, and affect the measured variables in different ways. Conceptual models of the periphyton–environment relationships observed are presented in graphical form. The knowledge generated provides background information required for fish culture management in periphyton-based ponds.

The Effects of Periphyton, Fish and Fertilizer Dose on Biological Processes Affecting Water Quality in Earthen Fish Ponds

The potential of periphyton-based aquaculture in South Asia is under investigation in an extensive research program. This paper is a further analysis of data from four experiments carried out in that framework, to explore periphyton, fish and fertilizer dose effects on water quality. Factor analysis and ANOVA models applied to a data matrix of water quality parameters in ponds with and without artificial substrates (bamboo poles and kanchi sticks), with and without fish (filter feeders catla and rohu, with and without bottom feeder kalbaush), and with a standard or 50% increased fertilizer dose, allowed us to identify the underlying ecological processes governing this novel periphyton-based pond system, and construct conceptual graphic models of the periphyton–environment relationships observed. We clearly established that the phosphorus flow is mainly linked to phytoplankton activity in the water column and decomposition on the pond bottom, while nitrogen flow is mainly linked to autotrophic (photosynthesis) and heterotrophic (decomposition and nitrification) processes that take place in the periphyton in addition to the water column and pond bottom. Consequently, disruption of the pond bottom by bottom feeding fish primarily promoted phosphate cycling and phytoplankton, while periphyton development on the supplied substrates and fertilization mainly improved oxygen balance and nitrogen related processes developing in the water column. The use of bamboo poles led to better results than kanchi sticks, related to the greater autotrophic periphyton development on bamboo and to the larger surface of bamboo poles that facilitate fish grazing and periphyton dislodgment that in turn have a renewal effect on periphyton. Stocking bottom feeding fish produces a fertilizing effect through the food web that benefits the filter-feeding fish and that makes it unnecessary to increase the dose of inorganic and organic fertilizers applied to the ponds. Thus, the output of this analysis will help the fish farmers in resource constrained countries to improve their production in periphyton-based ponds just by choosing bamboo substrates, stocking a bottom feeder fish together with the filter feeders, and saving money on fertilizers.

Development of a duckweed-fed carp polyculture system in Bangladesh

Abstract In an effort to develop a duckweed-based carp polyculture system, the effects of duckweed (Lemna sp.) application on pond ecology and fish production, and optimization of phytophagus Thai silver barb (Barbodes gonionotus) for this system were investigated in two separate experiments conducted at Mymensingh, Bangladesh. Duckweed had significant positive effects on growth rates of exotic Thai silver barb and common carp (Cyprinus carpio) and indigenous catla (Catla catla), whereas, indigenous rohu (Labeo rohita) was not affected by duckweed. A stocking density of Thai silver barb at the rate of 6000 fingerlings ha−1 with 3300 rohu, 3300 catla and 3400 common carp fingerlings ha−1 was found appropriate species mix for duckweed-fed polyculture system. This combination resulted in a net fish production of 2020 kg ha−1 during a 4-month culture period.