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Niche Measures and Feeding Strategies of Barbodes Gonionotus Bleeker and Oreochromis Spp. from a Rice Field in Bangladesh

A.K. Yousuf Haroon
Bangladesh Fisheries Research Institute, Riverine Station, Chandpur-3602, Bangladesh

Karin A. Pittman
Institute of Fisheries and Marine Biology, University of Bergen High Technology Center in Bergen, N-5020, Bergen, Norway

Abstract/ Executive Summary:

Intra-and interspecific virtual niche measures and feeding strategies of Barbodes gonionotus and Oreochromis spp. were studied from a rice field in Bangladesh. Appropriateness and ease of interpretation of different indices were evaluated. Small sizes of both species had a relatively wider dietary breadth and used many of the resource categories available to them than the large size groups, though none were generalistic feeder. The dietary overlap of large B. gonionotus on the small was greater than the reverse, but biologically insignificant. While the dietary overlap of large Oreochromis spp. on the small was significantly greater. Interspecific dietary width was relatively broader for B. gonionotus than Oreochromis spp. and overlap of B. gonionotus on Oreochromis spp. was significantly greater than the reverse. Evidence of significant intraspecific dietary overlap between the two sizes of tilapia reflects strong competition and cautions for mixed-size stocking in rice-fish system. Besides, there seems fewer opportunities for habitat segregation between B. gonionotus and Oreochromis spp., due to the significant interspecific dietary overlap of the former on the latter in rice-fish system. Tilapia specialized on periphytic detrital aggregate while silver barb tended to consume aquatic macrophrtes and molluscs. Small sizes of B. gonionotus should be preferred for rice-fish integration over the Oreochromis spp. due to their broader niche width and pronounced ontogenetic dietary shifts with the aging of the stock.

Keywords: Silver barb & tilapia, Intra- & interspecific niche indices, Rice-fish system

Location: Riverine Station, Chandpur, BFRI

Start Date: 00-07-1995

End Date: 00-09-1995

Program Area: Animal Health and Management

Commodity: Tilapia

Objectives:

To examine and compare the intra- and interspecific dietary breadth, the degree of diet similarity, overlap and feeding strategy of two size groups of B. gonionotus and Oreochromis spp.(O. mossambicus x 0. niloticus natural hybrid) and a single size group of B. gonionotus and Oreochromis spp., stocked in ricefields.

Methodology:

The present work comprises three experiments carried out in an experimental ricefield at the Riverine Station, Chandpur of the Bangladesh Fisheries Research Institute. Two size categories (around 6 and 12 em, total length) of B. gonionotus, were examined in the ricefield during April1994 (Experiment I), similarly two size groups of Oreochromis spp. were investigated during July 1995 ~Experiment II) and during September 1995 (Experiment III) a median size range (falling within 6 and 12 em) of both B. gonionotus and Oreochromis spp. were examined in the ricefield. The fish and sub-surface plankton were sampled every 3 h for 48 h in the intraspecific trials and for 24 h in the interspecific study for gut contents and available resources analysis. We have categorized the fishes in size classes, simply because fish farmers look first for the fish size rather than the weight when selecting any stock. Field preparation, fish stocking and sampling- Experiment I: Rice (transplant Aman: Paijam - a local variety of Oryza sativa) was planted in an experimental field of 166 m² (having a refuge canal of 1.0 m breadth and 0.5 m depth, on one side of the plot) according to farmers traditional practice. Once the tillers reached a height of 0.5 m and field conditions were as close as possible to those of a natural wet-season ricefield (water depth 0.25 m in the paddy field and 0.7 min the refuge), two sizes of B. gonionotus juveniles procured from the Riverine Station's hatchery were stocked at a total density of 7.0 juveniles/m² (581 individuals of each size). The small fishes were 4.5-5.52 cm (mean 4.85 cm) and 1.28-2.72 g (mean 1.72 g) and the large fishes were 11.54-13.4 cm (mean 12.64 cm) and 21.44-32.36 g (mean 27.81 g) at stocking. Prior to the experiment the fish had been fed a supplemental feed composed of 40% rice bran, 40% wheat bran and 20% fishmeal at 2-5% of body weight (bw) day· 1. Before stocking in the experimental ricefield the fishes were kept in a flowthrough system for 48 h to empty their gut contents. Two days after stocking, 10 fishes of each size were sampled every 3 h for a further 48 h with a knotless hapa net (3x2xl.5 m, mesh 0.5 cm). A total of 320 fishes (160 of each size) were collected. Experiment II: Paddies were prepared in the following year in the same way in the same field, and conditions as close as possible to the natural wet-season ricefield were established. Two size categories of Oreochromis spp. juveniles procured from the Riverine Station's other nursery ponds were stocked in the ricefield at a total density of 7.0 juveniles m^·2 (581 individuals of each size). The small fishes were 4.9-8.0 cm (mean 6.82 cm) and 1.92-8.15 g (mean 5.02 g) and the large fishes were 10.3-13.8 em (mean 12.0 cm) and 17.74-46.2 g (mean 27.84 g) at stocking. Prior to the experiment the fish had been fed a similar supplemental feed at the similar rates as for B. gonionotus. Stocked Oreochromis spp. had the same pre-treatment as B. gonionotus prior to release in the ricefield. A similar sampling regime was followed and a total of 320 fishes (160 of each size) were collected for gut analysis. Experiment III: The same ricefield preparation and fish treatment was used i:n the final interspecific experiment when both species were stocked together. In this case a single size of both B. gonionotus and Oreochromis spp. were stocked at a total density of 7.0 juveniles m^·2 (581 individuals of each species). The silver barbs were 5.1-10.1 cm (mean 7.1 cm) and 2.5-14.39 g (mean 4.86 g) and the tilapias were 7.5-10.2 cm (mean 8.53 cm) and 8.11-16.66 g (mean 10.48 g). A similar sampling regime was followed and a total of 320 fishes (160 of each species) were collected for gut analysis.

Source of Information: Bangladesh J. Fish. Res., 4(1): 13-26, 2000

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Significant interspecific dietary overlap of silver barb on tilapia cautions for mixed species stocking in the same system. It seems that there are less opportunities for habitat segregation between the B. gonionotus and Oreochromis spp. when stocked together in a rice-fish system. Mixed rearing of barbs and tilapia in the same habitat will likely result in a suppression of the growth of tilapia, due to their high degree of specialization on items with low nutrient value and their dietary overlap with barbs which have a broader niche width.

Knowledge Management: Journal