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Predatory Behaviour of a Perch, Nandus Nandusnandus Nandus

M. Das
Department of Aquaculture, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh

N. Akther
Department of Aquaculture, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh

M.A. K. Tarafder
Department of Aquaculture, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh

S. Pal
Department of Aquaculture, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh

Abstract/ Executive Summary:

Predatory behaviour of Nandus nandus was studied by offering Cyprinus carpio as prey. The study was conducted with six N. nandus (8.2 ±0.2 cm and 7.60 ±0.3 g) represented as P₁, P₂, P₃, P₄, P₅ and P₆. Three size categories of prey (C. carpio) such as small (2.0 ±0.1 cm and 0.23 ±0.01 g), large (3.6 ±0.1 em and 0.57 ± 0.01g) and mixed group consisting of both small and large prey were used for 14 days of trial. Predatory behavior was classified as targeting, driving, catching, handling, resting and next attempt of catching prey. After introduction of prey into the aquarium predators followed the movement of preys by eye movements and tried to target smaller one first. The predator grasped the head of the prey by its jaws by a drive and engulfed it wholly into the mouth. The average handling time (time taken to manipulate and swallow prey from capture to ceasation of pharyngeal movement) was 42±2 sec and 47±2 sec for small and large prey respectively. N. nandus were ingested more small prey than large prey though the size classes were equally available in case of mixed prey used. Although the prey consumption was higher in number when small prey were ingested but in weight the consumption was higher when ingested large size of prey. The study indicated that N. nandus, ingested more small prey and grasped the headfirst.

Keywords: Predatory behaviour, Nandus nandus

Location: Bangladesh Agricultural University.

Start Date: 00-00-1999

End Date: 00-00-1999

Program Area: Animal Health and Management

Commodity: Fish

Objectives:

(i) To determine the size specificity of the prey (C. catpio fry) taken by the N. nandus

(ii) To study the predatory behaviour (movements and activities) during feeding and just after feeding of N. nandus.

Methodology:

Investigation on predatory behaviour of N. nandus was carried out for a period of two weeks in July'99 where Cyprinus carpio fry were offered as prey in six glass aquaria (60x35x30 cm) marked as aquarium No.1, 2, 3, 4, 5 and 6. N. nandus having total length of 8.2 ± 0.2 cm and weighing of 7.60 ± 0.3 g were used as predator. Six predators were selected from the laboratory stock placed into six aquaria in the laboratory and water was aerated continuously to maintain dissolved oxygen level at high. Predators were treated with salt (1% dip for lhr) as a prophylactic treatment. The Predators were recognized as P₁, P₂, P₃, P₄, P₅ and P₆ following the corresponding number of the aquarium for the convenience of the study. Immediately after collection, the prey species were transferred into the laboratory and placed into a large stocking-tank. Fishes were kept into the tank without supplying any food for first two days. After that supplementary feed at the rate of maintenance ration (1% body weight) was supplied to the fish fry. Fish fry were then classified into two main size categories where small fry (total length of 2.0 ±0.01 cm and weight 0.23 ±0.01 g) and large fry (total length 3.6 ±0.1 cm and weight 0.57 ±0.01 g). Another group consisting of both small and large fry (50%+50%) was referred to as mixed size group. All three-size categories were offered as prey to N. nandus for the experiment in duplicate aquaria. Six preys were released into the aquarium containing a predator at 9 am everyday, after an hour the remaining prey(s) was removed by hand scoop net from each of the aquaria. Then fresh preys were offered to each predator as earlier at the same time of the following day. The number of prey eaten by each predator was recorded everyday This process was continued for 14 days to study the predatory behaviour of N. nandus.

Source of Information: Bangladesh J. Fish. Res., 5(2), 2001:197-200

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The predators consumed 0.064 to 0.121 g of prey per gram of predator per day. It was found that when the prey size was small the number of prey engulfed by the predator was greater but the consumption of prey in total biomass was higher when they consumed large prey.

Knowledge Management: Journal