Academic journal article Estonian Journal of Ecology

Comparison of Age Estimates from Otoliths, Vertebrae, and Pectoral Spines in African Sharptooth Catfish, Clarias Gariepinus (Burchell)/Otoliitide, Selgroolulide Ja Rinnauimekiirte Alusel Maaratud Vanuse Vordlus Aafrika Sagal Clarias Gariepinus (Burchell)

Academic journal article Estonian Journal of Ecology

Comparison of Age Estimates from Otoliths, Vertebrae, and Pectoral Spines in African Sharptooth Catfish, Clarias Gariepinus (Burchell)/Otoliitide, Selgroolulide Ja Rinnauimekiirte Alusel Maaratud Vanuse Vordlus Aafrika Sagal Clarias Gariepinus (Burchell)

Article excerpt

INTRODUCTION

Estimates of fish ages provide important demographic parameters to analyse and assess fish populations (Maceina & Sammons, 2006). Many structures have been used to estimate the age of fishes, including scales, otoliths, vertebrae, fin rays and spines, opercular bones, cleithra, urohyal bone, and hyomandibular bone. One of the main problems in age and growth studies is the selection of the most suitable structure to age the fish. Ages of fish are estimated by the comparison of age estimates from various bony structures and different readers (Barnes & Power, 1984). The most suitable ageing method may vary among species. Thus, the evaluation of the precision of bony structures by readers should be studied (Baker & Timmons, 1991). A measure of precision is a valuable means of assessing the relative ease of determining the age of a particular structure, of assessing the reproducibility of an individual's age determinations, or of comparing the skill level of one ager relative to that of others (Campana, 2001). Furthermore, ageing errors must be considered before deciding on the most reliable bony structure for the ageing of fish (Kimura & Lyons, 1991). Comparison of age estimates between structures is an alterative technique to validation that may provide useful information on the accuracy and bias of age estimating structures (Sylvester & Berry, 2006). Several studies have focused on comparing ages estimated from different bony structures in an attempt to quantify the most suitable age estimate and to identify possible bias associated with each structure. Comparisons of age estimates from various structures have been performed for many fish species, including black crappies, Pomoxis nigromaculatus (Kruse et al., 1993); yellow perch, Perca flavescens (Niewinski & Ferreri, 1999); river carp suckers, Carpiodes carpio (Braaten et al., 1999); channel catfish, Ictalurus punctatus (Buckmeier et al., 2002); thinlip grey mullet, Liza ramada (Gocer & Ekingen, 2005); common carp, Cyprinus carpio (Phelps et al., 2007); Tibetan catfish, Glyptosternum maculatum (Li & Xie, 2008); bull trout, Salvelinus confluentus (Zymonas & McMahon, 2009); as well as rohu, Labeo rohita; catla, Catla catla; and giant snakehead, Channa marulius (Khan & Khan, 2009).

The African sharptooth catfish, Clarias gariepinus (Burchell, 1822) is a benthopelagic, dioecious, omnivorous fish widely tolerant to extreme environmental conditions (Yalcin et al., 2002). Several researchers have studied its age and growth estimation by using different ageing structures such as spines (van der Waal & Schoonbee, 1975; Bruton & Allanson, 1980; Quick & Bruton, 1984), vertebrae (Pivnicka, 1974; Willoughby & Tweddle, 1978), and otoliths (Bruton & Allanson, 1980; Quick & Bruton, 1984). To the best of our knowledge the only paper available on comparison of age estimation in C. gariepinus deals with comparing age estimates obtained from pectoral spines and vertebrae (Clay, 1982). In a recent study (Weyl & Booth, 2008) saggital otoliths were validated for ageing C. gariepinus. There are, however, no published reports available on comparison of age estimates from otoliths, vertebrae, and pectoral spines, which are widely used for age estimation in C. gariepinus.

Therefore, the present study was undertaken with the following objectives: (1) to evaluate and compare age estimates of different structures (i.e., otoliths, vertebrae, and pectoral spines) between readers and between pairs of ageing structures and (2) to quantify potential biases of age estimates between readers and between pairs of ageing structures in order to select the most suitable bony structure for age estimation of C. gariepinus.

MATERIALS AND METHODS

Samples of Clarias gariepinus (N = 182) were collected monthly from the local fish market at Aligarh, U.P., India, during the period from May 2008 to April 2010. …

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