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Food and Feeding Habits in Respect of Length-weight Relationship and Condition of and Sex-ratio of Shrimp

Muhammed Shaf
Department of Zoology, University of Dhaka

M. M .A. Ouddus
Department of Zoology, University of Dhaka

Kh. G. Kibria
Senior Scientific Officer
Irrigation and Fisheries Development Scheme, Chandpur, Comilla.

Abstract/ Executive Summary:

Penaeus monodon, the tiger shrimp, was studied from the Sundarban estuarine and offshore waters during 1974-1975. Organic debris, crustacean remains, filamentous algae, molluscan shells etc were the principal food items of the shrimp. 52 % of the stomach contained no food. The length-weight relationships were expressed by the equations, Log w = - 5.8317 + 3.43104 Log TL for males, and Log W = - 5.03172+2.9668 Log TL for females. Smallest length-groups showed the highest condition values. 'K_n' values were the lowest in July and highest in October. Of the total specimens, 45.4 per cent was male and 54.6 per cent female in estuarine water, and 43.63 per cent male and 56.27 per cent female in offshore water.

Keywords: Shrimp, Sex-ratio, Feeding Habits

Location: Bagerhat, Rampal, Chournuhanv and Raimangal of the Sundarban estuary.

Start Date: 00-07-1974

End Date: 00-01-1975

Program Area: Animal Health and Management

Commodity: Shrimp

Objectives:

To identify food and feeding habits in respect of length-weight relationship and condition of and sex-ratio of shrimp

Methodology:

A total of 520 specimens of P. monodon was collected in seven monthly samples from four sampling centres, such as, Bagerhat, Rampal, Choumuhanv and Raimangal of the Sundarban estuary during the period from July, 1974 to January, 1975. These specimens, ranging from 51.0 mm to 160.0 mm in total length, were caught by behundi jal (purse net), moi jal (drag net) and ber jal (seine net). Besides, 190 specimens, ranging from 170.0 mm to 205.0 mm in total length, were also sampled from trawl-catches from the offshore waters of Khulna ground in the Bay of BengaI during the same period and were included in the present study. The specimens were preserved in five per cent formaIdehyde. For the study of food and feeding habits, stomachs of 56 specimens of varying lengths were examined. The cardiac stomach was opened longitudinally and food contents were taken in 70% alcohol in a petri-dish which was gratuated in squares Some bigger food items were studied under a magnifying lens. The qualitative and quantitative studies of the remaining food items were made under a binocular microscope. Prevalence of food items was determined by the occurrence method. To study the intensity of feedinq the stomachs were classified as full 3/4 full and so on according to the degree of distension. of stomachs as well as the quantity of food they contained. Shrimps 1/2 full stomach were taken to have fed actively. Length-weight relationship was calculated separately for male and female. Total lengths of the specimens were measured from the tip of the rostrum to the end of the telsion. Weights were taken by a double - pan balance. Both the sexes were divided' into fifteen length-groups of 10 mm class-interval for calculating the regression co-efficient by the method of least square. The relative condition factor, K_n, was calculated for each length-group of 10 mm class-interval for each sex and for each month. Sexes were separated mainly with the help of external genital characteristics. Males were separated with the help of petasma located on the protopodite of the first pair of pteopod and the females were separated with the help of the lycum found in between the base of the fourth and fifth pairs of pereiopods,

Source of Information: Bangladesh Journal of Agriculture, Vol-3, No-2,Page:398-403,Dec:1978.

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The overall proportion of males to females is shown Sex-ratio showed differences in various length-groups as well as in different months. A Chi-square test, however, showed no significant variation in sex ratio among the length-groups from the expected ratio of 1:1 either at 1 or 5 per cent level. The sex-ratios between the males and females of another penaeid shrimp, M. monoceros in Indian and Bangladesh waters have been studied. It was observed that the females slightly pre- dominated in all the months. So, it might be concluded that the females always outnumber the males in the shrimp populations.

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