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Determination of Breeding Season of Endangered Riverine Catfish Rita (rita Rita Hamilton, 1822) by Studying Ovarian Development and Gonado-somatic-index

M. L. Rahman
Department of Fisheries Biology & Genetics, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

M. F. A. Mollah
Department of Fisheries Biology & Genetics, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

Abstract/ Executive Summary:

Rita rita is an endangered riverine catfish having high market and nutritive values. The histological process of ovaries of Rita rita were performed to determine the breeding season for facilitating the artificial breeding in controlled environment. Fish were sampled monthly from the Brahmaputra River adjacent to Bangladesh Agricultural University (BAU), Mymensingh. The average Gonado-Somatic Index (GSI) ranged from 0.14 to 0.60 with the highest GSI value of 0.60 in July. The highest fecundity of 60114±3207.88 was found in the fish having length of 38.91±0.59 cm and weight of 1081.35±74.52 g. In contrast, the lowest fecundity was 37307.2±154.57 having length of 31.98±1.63 cm and weight of 810.87±49.75 g. The fecundity was found to increase with the increase of total length, body weight and the ovary weight and the relationship was linear and significant among them. Six developmental stages of ovaries were observed and categorized as the synchronous group. Vitellogenesis began in April with full development of ovaries in July. From this study, it can be presumed that gonadal development of R. rita peaked in July and breeding time within the months of June and July.

Keywords: Histology, Riverine catfish, Gonad, Gonado-somatic index

Location: BAU campus, Mymensingh

Start Date:

End Date:

Program Area: Variety and Species

Commodity: Cat fish

Objectives:

To determine the breeding season for facilitating the artificial breeding in controlled environment.

Methodology:

The samples of R. rita (Hamilton, 1822) were collected from the old Brahmaputra river adjacent to BAU campus, Mymensingh. At least five females were collected every month during first year study period. The total length and body weight of individual fish were measured first and then the ovary of each fish was taken out carefully and weighed using a sensitive portable electronic balance (Denver Instrument, XP-300; 3000×0.1g) to estimate GSI. Finally ovaries were preserved in 10% buffered formalin for further study. The GSI is frequently applied to determine the spawning frequency of fishes and calculated according to the following formula: GSI = (Weight of gonad/Weight of body) x100. In this method, 20 mg sample of ovary was taken separately from anterior, middle and posterior portions of each ovarian lobe accurately. The number of mature and maturing eggs from each portion was found out separately by actual counting due to small amount. The mean number of eggs in 20 mg sample was determined and then multiplied by the total weight of the ovary, which gave the total number of eggs i.e. the absolute fecundity of respective fish. The relative fecundity also are calculated by absolute fecundity/body weight. The preserved ovaries were taken out in a perforated plastic holder covering by perforated steel plates. Cleaning, infiltration and dehydration process were carried out in an automatic tissue processor unit using a series of alcohol of increasing concentrations, two times changes of xylene and finally through molten wax (three series). Paraffin embedded blocks were cut by microtome knife at 4-5 μm size and left the sections into a water bath at a temperature of 40^oC. The sections were placed on a glass slide and kept overnight on a slide drier hot plate at a temperature of 20⁰C. Then the sections were stained routinely with haematoxyline and eosin (Humason, 1972). The stained sections were mounted on the glass slide with Canada balsam and covered by cover slips and studied under a compound microscope (SWIFT M 4000-D). The photographic records were done simultaneously to study the different maturation stages oocyte and monthly developmental variations of ovary. Microsoft Excel (2003) was used to determine linear relationship and correlation co-efficient (r) between total length and fecundity, body weight and fecundity, gonad weight and fecundity following Zar (1984).

Source of Information: J. Bangladesh Agril. Univ. 11(2): 341–348, 2013 ISSN 1810-3030

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The average Gonado-Somatic Index (GSI) ranged from 0.14 to 0.60 with the highest GSI value of 0.60 in July. The highest fecundity of 60114±3207.88 was found in the fish having length of 38.91±0.59 cm and weight of 1081.35±74.52 g. In contrast, the lowest fecundity was 37307.2±154.57 having length of 31.98±1.63 cm and weight of 810.87±49.75 g. The fecundity was found to increase with the increase of total length, body weight and the ovary weight and the relationship was linear and significant among them. Six developmental stages of ovaries were observed and categorized as the synchronous group. Vitellogenesis began in April with full development of ovaries in July. From this study, it can be presumed that gonadal development of R. rita peaked in July and breeding time within the months of June and July.

Knowledge Management: Journal