Fixation, preservation and freezing effects on morphometrics of two fish species collected from Lake Ganvié, Benin, West Africa

The goal of this study was to evaluate the impacts of various preservation methods on disparities in morphometric parameters while also providing correction factors to re-calculate the original body dimensions when sampled fish are measured at a future date. In this study, adult samples of O. niloticus and C. gariepinus collected from the waters of the Republic of Benin, West Africa was measured directly after capture, then either frozen, preserved in 70% ethanol, or in 10% formalin. Ethanol and formalin solutions were prepared using tap and distilled waters. They were again measured after one week of the initial measurement and thereafter on a weekly basis for 20 weeks. Formalin and ethanol solutions showed to cause a decrease in the three morphometric characters, total, standard and head lengths. In contrast, frozen O. niloticus and C. gariepinus showed less shrinkage. Of the three preservation procedures, freezing obviously produced the least distortions. Therefore, freezing is recommended as the most desirable preservation method, particularly in multi-disciplinary studies on fish ecology. Equations to correct the effect of fixation, preservation and freezing on fish size are provided so they will assist in the future ecological and physiological studies to pool field and laboratory data.