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Pahutoxin 45

Figure 8 Chemical defense of fish.

of a surfactant but there is evidence that its strong ichthyotoxic effect is receptor mediated. The release of traces of such compounds in water is deterrent enough to prevent predators from attack.

The venoms of many fishes contain proteins that are very often labile and thus their characterization is complicated. The stingray (Potamotrygonidae) hides a powerful sting in its tail that it uses to wound aggressors and to introduce a proteinogenic poison. Often, fish use a combination of proteinous venoms together with neuroactive small molecules such as acetylcholine (e.g., Pterois volitans, firefish) that act synergistically.

Pufferfish (Tetraodontidae) are famous for the extremely toxic tetrodotoxin 34 that blocks sodium channels and leads to death quickly (LD50 (human) 10 mgkg-1). This poison is produced by symbiotic bacteria

(see Marine and Aquatic Defense Strategies). Apparently, some fishes evolved resistance against powerful toxins such as tetrodotoxin 34, saxitoxin 4, palytoxin 44, as well as polyether toxins (see previous discussion on ciguatera), which allows them to feed on producing organisms and to accumulate their toxins as weapon against predators (see discussion on sequestration in Animal Defense Strategies).

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