SCREENING FOR TOXIC ACTIVITY OF SOME MARINE BENTHIC ALGAE

This research was carried out in order to show that certain substances of algal origin are toxic to animals, particularly to fish, and to de termine if a relationship exists between toxicity and the latitude whe re the algae were collected. Twenty-nine species of algae were collect ed in different localities off the Pacific coast of Mexico. The sample s were frozen shortly after collection and kept frozen until used. Cru de ethanolic extracts of the algae were prepared and tested for ichthy otoxicity. The extracts were classified as nontoxic (NT), weakly toxic (WT) and highly toxic (with lethal effects) (T). The reactions exhibi ted by the fish to the presence of the algal extracts in their environ ment ranged from initial adaptative behaviour to death. Only four spec ies (14%) out of the 29 algal species tested were highly toxic, 13 (45 %) weakly toxic and 12 (41%) non-toxic. The high percentage of algal e xtracts that showed some degree of toxicity suggests that algae might have some kind of defence mechanism that could be noxious, thus being inedible by fish. The highest toxicity values were found among tropica l algae. These results suggest that a relationship could exist between toxicity and the latitude of the collecting locality.