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Studies on Periphyton Grazing Rate of Labeo Calbasu (hamilton)

M. M. RAHMAN
Department of Aquaculture, Bangladesh Agricultural University, Mymensingh, Bangladesh

S. M. RAHMATULLAH
Department of Aquaculture, Bangladesh Agricultural University, Mymensingh, Bangladesh

S. ISLAM
Department of Aquaculture, Bangladesh Agricultural University, Mymensingh, Bangladesh

N. T. NAREJO
Department of Fresh Water Biology and Fisheries, University of Sindh, Jamshoro, Sindh, Pakistan

M. M. HAQUE
Department of Aquaculture, Bangladesh Agricultural University, Mymensingh, Bangladesh

Abstract/ Executive Summary:

Studies were undertaken to investigate the grazing rate of Labeo calbasu on periphyton for a period of ten months from July 1998 to April 1999. It was observed that periphyton density significantly (p<0.05) influenced the grazing rate of L. calbasu. The lowest (0.0039 dmg/fish/4h) and highest (0.1037 dmg/fish/4h) grazing rates in the same size group of fish were found at 1 slide/aquarium (100 cm²) and 4 slides/aquarium (400 cm²) respectively. Similarly, size group of fish significantly (p<0.05) influenced the grazing rate. The lowest (0.0030 dmg/fish/4h) and the highest (0.0826 dmg/fish/4h) grazing rates were observed in smaller size and larger size group of fish respectively. However, significantly (p<0.05) high grazing rate (0.155 dmg/fish/4h) was observed in group than individual fish (0.060 dmg/fish/4h). The grazing rate was also significantly (p<0.05) influenced by time duration.

Keywords: Periphyton, Grazing rate, Labeo calbasu

Location: Faculty of Fisheries, Bangladesh Agricultural University, Mymensingh, Bangladesh

Start Date: 00-07-1998

End Date: 00-04-1999

Program Area: Animal Health and Management

Commodity: Carp fish

Objectives:

To determine the effects of different densities of periphyton, size group of fish interactions and time duration on grazing rate of L. calbasu.

Methodology:

Experimental period and location: The experiment was conducted for a period of ten months (300 days) from July 1998 to April 1999 in glass aquaria in the wet laboratory of the Faculty of Fisheries, Bangladesh Agricultural University, Mymensingh, Bangladesh. Collection and acclimatization of fish: The fish were collected from field hatchery of the Faculty of Fisheries and transported to the cisterns in oxygenated polythene bags. The fishes were kept in glass aquaria for acclimatization for 15 days. These were then grouped into different size groups on the basis of their length (cm) and weight (g) to serve the different purposes of the experiment. Experimental design: Scaling of substrate (roughned perspex slides) area with metabolic weight of fish. Scaling of tank to the standard length of fish (i.e. assuming that grazing rate of fish is influenced to a little extent by the space maneuverability). Periphyton was grown on both sides of roughened perspex slides in the cement cistern. The size of the slides ranged from 5 X 10 to 8 X 16 cm². Before the trial, faecal matter was completely removed from the aquarium by siphoning. Experimental system: Static system consisting of 12 glass aquaria (70 X 35 X 25 cm³) of 60 l (for 14- 16 cm and 19-21 cm size group of fish) and 12 glass aquaria (48 X 28 X 25 cm³) of 30 l (for 4-6 cm and 9-11 cm size group of fish) were used. The system was enclosed by black screen to protect the fish from undue external visual disturbance and the top of the aquarium was covered using a fine mesh net. The slides were suspended horizontally in the periphyton stocked cistern at about 10 cm below the water surface for three weeks before starting the grazing experiment. Then the acclimatized fish were measured (length and weight) using measuring board (TL precision 1 mm) and electronic balance (BDH-100 D, precision, 0.1 g). Finally these were transferred to clean aquaria and kept without feeding for 48 h. During the trial, the required number of labeled (at both ends) periphyton covered slides were collected from the stock cistern and suspended in water. The periphyton was then scraped using a sharp knife from one half of the slide and transferred to pre-weighed and labeled pieces of aluminum foil and the other half with periphyton were transferred to aquaria. After required period of time (three weeks), the slides were collected and all remaining periphyton were scraped and placed on the weighed and labeled aluminum foil. Then the aluminum foils were placed in an oven for drying at 115ºC for 24 h and kept in a dessicator and then weighed. The grazing rate was estimated by deducting the weight obtained for second half from that of the first half. Experiment I: The grazing rate of L. calbasu was determined using same size group (9-11 cm) of fish at different periphyton densities (100 cm², 200 cm², 300 cm², 400 cm², 500 cm² and 600 cm² area) with two replications. Single fish was allowed to graze in a single aquarium. The duration of grazing was 4 h. Experiment II: In this experiment, 4 different size groups of fish were used to observe the grazing rate. Single fish was allowed in a single aquarium with 400 cm² slide area over 4 h grazing period. Twelve glass aquaria were used for the 4 treatments with three replications each. Experiment III: In this experiment 1, 2 and 4 fishes of the same size (9-11 cm) group were allowed in an aquarium in order to determine the single and group wise grazing rate. The average body weight of fish was 12.0 ± 0.20 g. Grazing rates for one hour at different stocking densities of fish were designated as treatments with three replications. Experiment IV: Fishes were placed individually in separate aquaria to find out the grazing rate at different time duration. The durations viz. 1, 2, 4 and 6 h were considered as four treatments, with three replications. Data analysis: Comparison of treatment means was carried out using one-way analysis of variance (ANOVA), followed by testing for pair-wise differences using Duncan’s Multiple Range Test. All statistical analyses were done using MSTAT-C statistical package.

Source of Information: Indian J. Fish., 54(4) : 365-369, 2007

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

L. calbasu showed increasing grazing rate up to 4th hour after which the grazing rate remained almost constant.

Knowledge Management: Journal