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Determination of the Age and Growth of Glossogobius Giuris (hamilton-buchanan, 1822) Using Sectioned Otolith

Md. Sagir Ahmed
Department of Zoology, University of Dhaka, Dhaka-1000, Bangladesh

Gulshan Ara Latifa
Department of Zoology, University of Dhaka, Dhaka-1000, Bangladesh

Abstract/ Executive Summary:

The freshwater gobi, Glossogobius giuris is an important freshwater fish species in Bangladesh. The age and growth of this species, collected from the river Titas, Brahmanbaria, were studied with transverse sections of otoliths. The otolith’s opaque zones that are formed every year were the annual rings. The growth of this species was rapid during the first two years, reaching 18.5 cm in total length. Most of the specimens were 1-2 years old and accounted for 90% in total. The maximum age recorded was five years with 19.5 cm in total length. The von Bertalanffy growth parameters L∞ and K for this species were 19.58 cm and 1.36/year, respectively. The study indicated that the age and growth of G. giuris can be determined using its sectioned otolith.

Keywords: Glossogobius giuris, Otolith, Age and growth.

Location: The river Tias, Brahmanbaria, Bangladesh

Start Date: 00-06-2006

End Date: 00-05-2007

Program Area: Animal Health and Management

Commodity: Fish

Objectives:

To determine the age and growth of G. giuris with the expectation that information on such aspects of the biology of this fish would ultimately help in adopting proper management and conservation of this important fish.

Methodology:

A total of 1837 specimens of G. giuris was sampled from the river Titas, Brahmanbaria from June 2006 to May 2007. Most specimens were caught with gill nets and long lines. The total length (TL) of each fish was recorded to the nearest mm from the tip of the snout to the tip of the caudal fin and weighed upto nearest gram using specific weight balances depending on the size of the fish. Only 54 specimens of different sizes were selected for otolith collection. Otoliths were removed from the fish, washed with tap water, and then kept in dried condition. The right otoliths (sagittae) were used for age determination; the left sagittae were used if the right sagittae were damaged when extracted from the fish or during the sectioning process. The dried otoliths were then brought to the laboratory of Marine Biology and Oceanography, Faculty of Fisheries, Kagoshima University, Japan, for further processing. The length of otoliths was measured under a microscope (Olympus SZ-40, Japan) and weighed with a balance (Satorius 2462, Zeiss, Germany). Measured otoliths were embedded in epoxy resin, a mixture of Dodencenyl Succinic Anhydride (DDSA), Epok 812 (Epoxy equivalent 148), Methyl Mandic Anhydride (MNA), Dimethyl Aminomethyl Phenol (DPMP) (4.8:2.2:3.2). Embedded otoliths were cut with a microcutter (Model MC-201; Maruto Co., Ltd., Tokyo, Japan) and polished using a grinder (Model 9820; Makita Co., Ltd., Tokyo, Japan) in order to make transverse sections crossing the focus, leaving a thin slice of approximately 0.2 mm thick, and mounted on a glass slide and coated with nail enamel. The number of ring marks (outer edge of opaque zone) on the sectioned otoliths was counted using a microscope (LEICA MZ 12.5; Leica Microsystems, Heerbrugg, Switzerland) with transmitted light under a black background at 40x magnification. The annuli were counted by two readers and if there was an agreement between both readers, the resulting counts of the annuli was adopted. The ages were assigned to every individual according to the number of opaque zones observed in sectioned otolith. The monthly length frequency data of G. giuris were analyzed using FiSAT (FAO-ICLARM Stock Assessment Tools) as explained in details by Gayanilo et al. (1996). The fitting of the best von Bertalanffy growth curve was based on the ELEPHAN-I program (Pauly and David 1981), which allows the fitted curve through the maximum number of peaks of the frequency distribution. With the aid of the best growth curve, the growth constant (K) and asymptotic length (L∞) were estimated.

Source of Information: Bangladesh J. Zool. 40(1): 13-19, 2012

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Around the world, the ages of many fishes are determined each year using otoliths. Fish age is generally determined after initial preparation of the otolith (such as embedding and thin sectioning) followed by microscopic examination and counts of the annual growth zones (annuli). The preparation process is often time consuming, while the interpretation of the annuli requires skilled technicians. The present study demonstrates that year marks or annuli are formed in the otolith of G. giuris and age determination is possible through counting of the year marks.

Knowledge Management: Journal