Growth changes induced by gamma radiation on Biomphalaria straminea (Dunker, 1848)

Abstract

Doses of 60 Co gamma radiation with 2. 5; 5; 7.5; 10; 15; 20; 25; 30; 35; 40; 45; 50; 55; 60; 80; 160; 320 and 640 In order to study controversial aspects in B. straminea shell development following exposure to ionizing radiation, the growing behavior of this epidemiological vector of schistosomiasis after exposure to low intensity gamma rays was studied, in colonies (cross fertilization) and sexually segregated (self fertilization) situations. MATERIALS AND METHODSA population of 1,080 snails of B. straminea, BH breed obtained from Centro de Pesquisas Aggeu Magalhães-Fiocruz, was exposed to gammarays obtained from a 60 Co source receiving doses of 2. 5; 5; 7.5; 10; 15; 20; 25; 30; 35; 40; 45; 50; 55; 60; 80; 160; 320 and 640 Gy, applied to groups of 30 snails per dose. An additional group of 60 non irradiated (0 Gy) snails was kept as control.The mollusks were bred from eggs laid with a maximal difference of two days and were raised in laboratory for approximately 50 days. All snails were in a reproductive development stage.Fifty percent of the studied population was kept in colonies and the other half was maintained isolated in sexual segregation, allowing cross fertilization and self fertilization, respectively, in each set. Consequently, the snail in each groups/dose were placed in individual (isolated) and collective (colony) aquariums with the ratio of water volume/ snail (50 ml) kept constantly replenished with water (25°C ± 2°C and pH 6.6-6.8) during the period of observation.The irradiation of the snails by gamma-rays was done with groups of 30 snails held inside glass The embryological development of snails is particularly affected by ionizing radiation as stated by Liard et al. (1968), Okazaki et al. (1996), Melo et al. (1996) and Melo (1998). A previous report stated that following irradiation with gamma rays, a cessation in the development of the shell may occur (Perlowagora-Szumlewicz & Berry 1964). Snails of different ages showed the same shell diameter as observed by Rey (1967), Leal (1976), Rozenberg (1989) and Carvalho (1992 tubes by dose and placed in gamma-cell irradiator, model RL-60, from Radionics Laboratory, with dose rate of 0.97 Gy per minute. In order to avoid copulation during the exposure time, the snails were separated by a thin cotton cushion, in the isolated set of mollusks. The control group remained in a dark environment for the same time as the maximal (640 Gy) irradiation was applied in order to have the same conditions of temperature and humidity as those used in the irradiation procedure.The diameter was measured daily by means of a caliper applied to the major shell diameter, with the sites used for measuring marked with white ink. RESULTS

Gamma 60Co DL50/30 of Biomphalaria glabrata (Say, 1818)

“…LIARD et al 4 , noted that the whole B. glabrata group irradiated with gamma-rays dose of 320 and 640 Gy died after 60 days, but in a previous work 7 it was found that all B. straminea snails died around the 11 th to the 18 th day under the same doses. This fact implies in a higher radio-resistance of B. glabrata as compared to B. straminea.…”