NORTH-WESTERN JOURNAL OF ZOOLOGY 7 (1): 178-180 Article No.: 101401
©NwjZ, Oradea, Romania, 2011 www.herp-or.uv.ro/nwjz
Determination of the best length measurement of fish Bahadır ÖNSOY, A. Serhan TARKAN, Halit FİLİZ* & Gökçen BİLGE Mugla University, Faculty of Fisheries, Dept. of Hydrobiology, 48000, Kotekli, Mugla, Turkey * Corresponding author, H. Filiz, phone: (+90) 252 2111895, fax: (+90) 252 2111887, e-mail:
[email protected] Received: 11. September 2009 / Accepted: 14. December 2010 / Available online: 20. December 2010
Abstract: Standard (SL), fork (FL) and total lengths (TL) of three common freshwater fish species, goldfish Carassius auratus (L.), gibel carp Carassius gibelio (L.) and common carp Cyprinus carpio (L.) were examined to determine the most consistent length measurement of fish and possible bias source of multiple measurements of the same sample by different persons based on statistical comparisons. Index of Average Error (IAE) suggested that measurement of TL had significantly lower average errors compared to SL and FL for all species (p0.05) (Table 3). Indeed, p value was highest in TL, followed by FL and SL.
Discussion Differences between the length data mostly depend on the sample quality. For example in fish, there might be defections (e.g. lost or damaged tail either by predators or samplers). Preservation techniques likely have the most profound effect on fishes which may cause considerable sample shrinkage (e.g. Quiñonez-Velázquez 1996, Thorstad et al. 2007). Indeed, in fish collections SL is preferred as the caudal fin becomes brittle over time and may break off. Thus, if measurements on a museum specimen over time were compared, SL would have a lower error range than TL and FL. Some other fishes have different kinds of body shapes that confuse which equipment and/or measurement type should be useful to take length measurements. For instance, in species with rigid caudal fins such as tuna and billfish, FL is frequently used instead. However, all of these factors caused variation among measurements taken by different observers even on the same sample. In
Table 1. IAE values for three examined fishes. TL were significantly lower than SL and FL at P = 0.001 for all species. Species Measurement type IAE
Goldfish (n= 70 ) SL FL TL 2.27 2.31 1.23
Gibel carp (n= 98 ) SL FL TL 1.68 1.58 1.23
Common carp (n= 42 ) SL FL TL 1.59 1.68 1.22
Table 2. Conversion formulas of three examined fishes. Goldfish TL = 1.3574*(SL) – 5.7059 FL = 1.0963*(SL) + 5.3622 FL = 1.2259*(TL) – 10.974
Gibel carp TL = 1.2602*(SL) + 2.136 FL = 1.1284*(SL) + 2.1338 FL = 1.1157*(TL) – 0.1301
Common carp TL = 1.2645*(SL) + 2.7014 FL = 1.0695*(SL) + 5.8308 FL = 1.1815*(TL) – 4.073
Table 3. Descriptive statistics and ANOVA results for personal measurements of different type of lengths for three examined fishes. All comparisons gave no significant result (p>0.05). Species Measurement type Min-Max F P
SL 75-125 1.389 0.246
Goldfish FL 88-143 0.197 0.890
TL 104-158 0.315 0.815
SL 50-122 0.205 0.892
Gibel carp FL 59-142 0.039 0.989
TL 66-157 0.178 0.911
SL 93-172 0.052 0.984
Common carp FL TL 104-187 119-217 0.139 0.064 0.937 0.979
Önsoy, B. et al.
180 that case, scientists need the most reliable body length measurement method for all samples including damaged ones. There may be a number of factors which affect the proportion of SL, FL, and TL of fishes including growth phase, food availability and quality, size range, health and general fish condition and preservation techniques as well as sampling procedure, namely sample size and length range (e.g. Gaygusuz et al. 2006). Even in measurement of the same fish species, many discrepancies could appear because of precision and accuracy of the instrument used to measure the specimen (dial callipers vs. needle pointed dividers) or the disagreement in standardized protocol to measure the lengths (Howe 2002). For instance, there are many different definitions or methods for standard length which make the standardization quite difficult (Howe 2002). However, based on the results of this study, it can be suggested that personal length measuring errors could be neglected if the researcher is experienced and the protocol well designed. This study suggests that, at least for a standard body shape (i.e. most of cyprinids), TL should be used rather than SL or FL. However, analyses in this study should be expanded to include other type of body shapes and find out which length measurement should be taken into consideration for each body shape. Also, the results encourage the taking of multiple measurements of the same fishes from one population as long as the measurers have sufficient experience to measure fish. Finally, if possible, taking each length measurement and giving the conversion formulas in the papers, will certainly be helpful for the researchers to compare their results especially when the relevant equations are not suitable to establish for rare species in a specific locality.
Acknowledgements. The authors wish to thank Özcan Gaygusuz who helped with the statistical analyses and Meltem Filiz for helping to collect specimens.
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