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RESEARCH ARTICLE
Contents Vol 56(5)

Fluctuating asymmetry in fish otoliths and heterozygosity in stressful estuarine environments (West Africa)

Jacques Panfili A D , Jean-Dominique Durand A , Khady Diop A , Béatrice Gourène B and Monique Simier C
+ Author Affiliations
- Author Affiliations

A IRD, B.P. 1386, 18524 Dakar, Senegal.

B Université d’Abobo-Adjamé, 02 BP 801, Abidjan 02, Ivory Coast.

C Centre de Recherche Halieutique IFREMER/IRD, avenue Jean Monnet, B.P. 171, 34203 Sète Cedex, France.

D Corresponding author. Email: panfili@ird.fr

Marine and Freshwater Research 56(5) 505-516 https://doi.org/10.1071/MF04138
Submitted: 12 July 2004  Accepted: 2 March 2005   Published: 21 July 2005

Abstract

Fluctuating asymmetry (FA) is assumed to reflect the developmental instability caused by environmental or genetic stress. Fish otoliths represent a very good tool for investigating the consequence of different effects on FA. Otolith FA analysis, coupled with genetic analysis, has been undertaken on two common West African estuarine species, Ethmalosa fimbriata (EFI) and Sarotherodon melanotheron (SME), in two neighbouring estuaries, in order to highlight the impact of salinity on developmental stability. The Gambia estuary has a normal functioning and the Saloum estuary is inverse (saltier waters in the upper river), reaching extremely high salinities (>100 psu) and constituting severe environmental stress. Five sub-populations of EFI and six of SME were studied along a salinity gradient. The differences between right and left otoliths were estimated with image processing by measuring five dimensions (area, perimeter, diameter, rostrum and posterior radii). Analyses of genetic differentiation at three EPIC and one anonymous nuclear gene loci for EFI and six polymorphic enzymatic loci for SME were carried out to measure the level of heterozygosity. Absolute FA in all otolith traits examined was unaffected by gender but increased significantly with fish size. Size-corrected absolute FA did not show any significant difference among sites differing largely in salinity, although a higher asymmetry in otolith area was recorded in the saltiest site. These findings suggest that otolith asymmetry is a poor indicator of osmotic stress. The individual heterozygosity level did not seem to have an effect on otolith FA for either species, even though a slight correlation appeared with otolith area or perimeter. Otolith FA cannot be considered to be a useful indicator for estimating changes linked with environmental or genetic stress in these estuaries.

Extra keywords: bio-indicator, environmental stress, Ethmalosa fimbriata, Sarotherodon melanotheron.


Acknowledgments

We would like to acknowledge O. ‘Petit’ Diouf, J. Raffray and O. Sadio for their help during samplings. We are also very grateful to the fishermen in the Saloum, A. Diop, S. Thiam, A. Sarr, and I. Fall, and in Gambia, F. Dramme, I. Jammeh and S. Guisse. We specially thank B. Guinand (Montpellier University II, France) for his help with the bibliography, and finally G. Begg and two anonymous reviewers for very constructive comments.


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