Exposure of Nile Tilapia (Oreochromis niloticus) Fingerlings to a Saxitoxin‐Producing Strain of Raphidiopsis (Cylindrospermopsis) raciborskii (Cyanobacterium) Reduces Growth Performance and Increases Mortality Rate

Abstract

Blooms of toxin‐producing cyanobacteria have been more frequent and lasting because of the eutrophication of freshwater ecosystems, including those used for aquaculture. The aim of the present study was to investigate the effects of chronic exposure to a saxitoxin‐producing strain of Raphidiopsis (Cylindrospermopsis) raciborskii on the performance of Nile tilapia (Oreochromis niloticus) fingerlings over a 60‐d period. The fingerlings were cultivated under the following conditions: 1) water without cyanobacterium (WATER), 2) R. raciborskii in ASM‐1 culture medium (CYANO), and 3) ASM‐1 culture medium without cyanobacterium (ASM). Exposure to the CYANO treatment led to a significant increase in the mortality rate (p < 0.05) and a significant reduction in growth (p < 0.05) compared to fingerlings submitted to the ASM and WATER treatments, in which similar survival and growth were found (p > 0.05). Saxitoxin toxicity was dependent on the weight of the fingerling (p < 0.05), with maximum mortality caused by the ingestion of 13.66 μg saxitoxin equivalent L−1 g−1. The present results clearly show the harm caused by saxitoxins to the production of Nile tilapia fingerlings in the early growth phase. These findings underscore the importance of maintaining adequate water quality in aquaculture activities to minimize the risk of saxitoxin‐producing cyanobacterial blooms and avoid economic losses among producers. Environ Toxicol Chem 2020;39:1409–1420. © 2020 SETAC

Cyanotoxins and Food Contamination in Developing Countries: Review of Their Types, Toxicity, Analysis, Occurrence and Mitigation Strategies

“…On the other hand, Galvão et al proposed a depuration period of five days for the STXs accumulated in Nile tilapia muscles to reach undetectable levels [93]. The toxic effects of STXs on the survival and growth performance of Nile tilapia fingerlings were shown to be dependent on their weight (more mortality in the exogenous feeding phase) [170]. Samples of Geophagus brasiliensis fish from the Alagados reservoir were all contaminated with PST (gonyautoxins) with similar levels in all sampling seasons (spring 2007, summer, and autumn 2008), and these levels (in STX eq./100 g) were safe in all the positive samples [95].…”