Could ciguatoxins cause structural changes in fish tissue?

Ciguatera poisoning (CP) is a foodborne illness of significant public health concern, which is caused by the consumption of fish contaminated with ciguatoxins (CTXs), lipophilic neurotoxins that bioaccumulate throughout the marine food web. Despite its global relevance, the specific morphological and ultrastructural effects of CTX exposure on fish tissues remain poorly understood. This study aimed to characterize histological and ultrastructural alterations induced by dietary CTX exposure and how toxins accumulate in tissues of the dusky grouper (Epinephelus marginatus).

Captive-born dusky groupers were fed an experimental diet composed of CTX-contaminated amberjack and dusky grouper tissue, with an average concentration of (0.109 ± 0.003 ng Eq. CTX1B/g of flesh). Tissue samples were collected at 24, 60, and 108 days. CTX estimation was performed using a cell-based assay in the liver, muscle and gonads, and histological examinations of liver, kidney, gonads, muscle, and intestinal tissues were conducted. Additionally, hepatic samples were analyzed by light and transmission electron microscopy.

Histopathological findings included cytoplasmic vacuolization, localized inflammation, and increased connective tissue development. Ultrastructural analysis showed signs of hepatocyte necrosis, nuclear condensation, and displacement of cellular organelles in CTX-exposed individuals. Despite toxin exposure, tissue alterations were mild and predominantly localized to the liver, with no significant histological changes detected in the intestine, gonads, or muscle. CTX accumulation was first detected in the liver and gonads, with hepatic toxin levels peaking at 60 days (0.868 ± 0.121 ng Eq. CTX1B/g) and subsequently declining, while gonads exhibited a delayed increase in toxin concentration.

These results demonstrate that dietary exposure to CTXs induces significant hepatic structural damage in E. marginatus and that toxin distribution across tissues evolves over time. This study provides experimental evidence supporting the role of sublethal CTX exposure in the onset of tissue-specific damage in adult reef fish under toxin concentrations relevant to natural environmental conditions.