Abstract
Age determination or growth rate of fishes is a critical component of a proper fishery management. Current methods of fish age determination or growth rate have several drawbacks, including, large numbers of fish needed over time for analyses, subjective interpretations during age determination or the use of expensive instrument for analysis. In this report, a simple theoretically derived mathematical formula is assessed for prediction of fish growth in length. Secondary data of length measures of 16 different species of tropical marine fish was used to assess the accuracy of the formula for predicting fish growth. The data comprised of relative length-at-age of 14 different fishes and absolute length (in centimeters) of 2 other different fishes. For each species, two of the length measures together with the corresponding ages were used to estimate two constants in the formula and the formula used to predict the remaining lengths. The accuracy of the formula for prediction was assessed by evaluating the discrepancies between observed data and corresponding predicted data. The biasness as well as the accuracy of the formula was also assessed. In all the species studied, discrepancies between observed data and the corresponding formula predicted values were minimal and fluctuated between negative and positive values. The mean signed value of the discrepancies (a measure of biasness) for all the 16 species was -0.2 ± 1.7, while the mean of the absolute discrepancies (a measure of accuracy) was 1.2 ± 1.4. The fluctuations of the discrepancies between negative and positive values demonstrate that the discrepancies are not systematic errors of prediction. The signed mean discrepancy of -0.2 is close to 0, thus indicating minimal biasness of prediction. Also the absolute mean discrepancy of 1.2 suggests prediction accuracy within 1 unit of actual measurement, indicating high accuracy. Key words: Tropical fish, demersal marine fish, fish length prediction, growth rate, age determination, discrepancies.
Highlights
Age determination of fishes is a critical component of a proper fishery management; and some conventional techniques have been used for direct age determination of fishes
All the plots are fairly linear, indicating that the square of fish length is linearly dependent on age (L age)
It is important to note that prediction accuracy was similar and minimal in most cases across all the species and fluctuated between negative and positive values, demonstrating that the discrepancies were not systematic errors of prediction
Summary
Age determination of fishes is a critical component of a proper fishery management; and some conventional techniques have been used for direct age determination of fishes. These include the growth zones analysis of skeletal-structures (Bagenal, 1974; Brennan and Cailliet, 1989; McForlane and Beamish, 1995), the tag-recapture technique (Cailliet, 2001) and the length-frequency analysis technique (Ricker, 1975).
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