Effect of temperature and feed rate on the body shape of Oreochromis shiranus, a widely-cultured tilapia species in Malawi

Kassam D,Likongwe S,Ssebisubi M

doi:10.21608/eajbsz.2012.14302

Abstract

Considering the vitalness of traits such as body shape and size in influencing the marketability of fish, geometric morphometrics was utilized to explore if raising fish at different temperatures and feedrates would affect such important traits. MANOVA revealed significant differences in body shape among fish raised at different temperatures but not those fed at different levels of their body weight. In general, the fish that were raised at 20°C, regardless of the feedrate, had shorter but deeper bodies, larger eyes and longer heads as opposed to the longer and slender bodies, smaller eyes and shorter heads found in those reared at 25°C and 30°C. On size, ANOVA revealed significant differences along temperature and feedrate gradients in a way that fish reared at 20°C were the smallest, followed by those at 25°C and then the largest were those at 30°C. On feedrate, it was only at 30°C where fish fed at 6% body weight were significantly larger in size than those fed at 3% body weight. These findings are discussed in terms of best management practices, especially on how to combine such two abiotic factors in order to maximize growth within the shortest period possible, considering the economical implications.

Highlights

IntroductionAquaculture production in Malawi is still very low and hinges on very few tilapia species (contributing about 93% of total production), namely: Tilapia rendalli, Oreochromis karongae and O. shiranus, and one catifsh species, Clarias gariepinus
Aquaculture production in Malawi is still very low and hinges on very few tilapia species, namely: Tilapia rendalli, Oreochromis karongae and O. shiranus, and one catifsh species, Clarias gariepinus
The aim of this study is to utilize geometric morphometrics to uncover the effect of temperature and feed rate on the shape and size of widely cultured O. shiranus, and make geometric morphometrics known to Malawian aquaculturists who can add it to their tool kit when it comes to fish quality assessment

Summary

Introduction

Aquaculture production in Malawi is still very low and hinges on very few tilapia species (contributing about 93% of total production), namely: Tilapia rendalli, Oreochromis karongae and O. shiranus, and one catifsh species, Clarias gariepinus. Of the abiotic factors that constrain tilapia production in Malawi and other African countries, temperature features highly as this varies from place to place and season to season throughout the year. Considering that fish are poikilotherms, water temperature is a critical factor since it influences several biological processes, including survival, feed utilization and in turn growth. Physiological processes that control growth, survival and reproduction in fish bear a positive relationship with water temperature (Atwood et al, 2003). Water temperature interacts with other management practices such as stocking density and feed composition to affect growth of tilapias (Musuka, 2006). It is necessary to optimize these rearing conditions, i.e. temperature and feeding levels, due to their direct bearing on the growth performance of fish, in order to boost aquaculture production. Several researchers have investigated how fish form is affected by abiotic factors like temperature, salinity etc. (see Hubbs, 1926; Barlow, 1961)

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