author(s)
Md. Fazlul Haque, Sabina Sultana, Moni Krishno Mohanta and Md. Ariful Hasan

abstract
Formalin, a carcinogenic agent, is illegally used for preservation of fruits and fishes in Bangladesh. It is often observed that flies are avoiding some fruits and fishes for an unknown reason in fruits and fish markets. Therefore, it was assumed that flies may avoid the contaminated fruits and fishes by detection of presence of formalin in those items. Hence, this study was designed to uncover relationship between rate of avoidance of the fishes by flies and the concentration of formalin for contamination. For this study, five types of fruits viz. Mango, Orange, Apple, Papaya and Banana, and two types of fishes, viz. Puthi, Puntius titus (Hamilton, 1822) and Tilapia, Oreochromis niloticus were soaked with normal water (Control) and 120 ppm, 250ppm, 500ppm, 750ppm, 1000ppm and 2000ppm solution of formaldehyde for 1 minute. Then fruits and fishes were kept in different Petridis separately in open place for 1 hour to count the flies available on fruits and fishes. Finally, the counted number was analyzed with Graph Pad Prism software. It was found that number of flies in all samples of fruits and fishes was decreased gradually from the lowest concentration of formalin (250ppm) to the higher concentration indicating that flies can detect the presence of formalin in fruits and fishes even in the lowest concentration (250 ppm). However, the initial concentration of formalin which was significantly avoided by flies was different for different types of fruits and fishes. Altogether, it can be concluded that formalin contamination is one of the reasons of avoidance of fruits and fishes by flies.