Data of Thesis
Author: Rodrigo de Cássio da Silva
Title:.Bioaccumulation and depuration of the cyanobacterial toxin cylindrospermopsin and its effects on growth in the juvenile tilapia (Oreochromis niloticus)
Year: 2008. Full text (in Portuguese)
Abstract
Cylindrospermopsin (CYN) is a toxic alkaloid produced by several genera of cyanobacteria and is implicated in human and wildlife poisoning incidents. The principal mode of action for CYN is protein synthesis inhibition, but the sublethal effects of this toxin in aquatic organisms, including changes to development and behavior, have been poorly studied. Little information is available regarding bioaccumulation of CYN in these organisms. This study examined its bioaccumulation, depuration and effects on growth in the juvenile tilapia (Oreochromis niloticus) exposed to freeze-thawed whole cell extracts and whole cells of toxic (Cylindrospermopsis raciborskii). Four experiments under laboratory conditions with these fish were done. In the first one the animals were fed for 15 days with fish food plus cells extracts (0.5 g food.day-1. fish-1) containing 0.31 μg CYN .g-1 food. Every three days for a fifteen day period, fish were collected. In the second trial, fish were fed during 30 days and the fish food (0.5 g food.day-1. fish-1) contained 0.35 μg CYN .g-1 food. After 15 days, fish were collected each 3 days. In the third trial fish received (0.5 g food.day-1. fish-1), during 12 days, fish food with cells extract at a higher toxin concentration (0.8 μg CYN .g-1 food). In the following 10 days, the animals were fed (0.5 g food.day-1. fish-1) without toxic cells extracts. The fourth trial, fish received (0.5 g food.day-1. fish-1), during 15 days, food plus whole cells of C. raciborskii (5.4 μg CYN .g-1 food). Fish weight and length were measured, its samples of muscle tissue and viscera, in all trials, were extracted with water and 100% methanol, filtered, evaporated and resuspendend in water and analyzed by ELISA imunoassays. It was verified that CYN exposed animals had their biomass and sizes reduced in relation to non-exposed fish in the trial 1, but not in the others trials. In the first trial the higher concentration of CYN in muscle tissue was observed on third day, tending to reduce on day with oscillations throughout the time. Viscera showed the maximum concentration on third day and presented the same concentration oscillation pattern throughout the time. In the second trial, maximum concentration was found in the first sampling day on muscle tissues (19th day – 0.15 ng CYN.g-1) and viscera (7.83 ng CYN.g-1). In the depuration experiment (3rd trial) the concentration found in muscle tissue and viscera, in depuration period, were almost the same found on first sampling day. In the last trial (4th trial), highest concentrations of CYN in muscle tissue was found on 12nd day (2.3 ng CYN. g-1). But in viscera, the higher concentration was found on 15th day (21.1 ng CYN. g-1). Studies of CYN distribution in animal tissues showed that the majority of this toxin is observed in viscera, resulting from the consumption of toxin-containing food. In this study we have noted a bi-phasic pattern of CYN throughout the time and it could be attributed to the detoxification process. These results do not corroborate other works since fish accumulated CYN when nourished with cellular extracts more than toxic cells. This is the first investigation of CYN bioaccumulation in tilapia and indicates the importance of continuous monitoring of this compound in organisms for human and animal consumptions.
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