Effects of okadaic acid and dinophysistoxins on swimming and metabolic fitness of marine fish

Harmful algal blooms (HABs) are natural occurrences that can severely impact marine communities. Depending on the species, they can produce a wide array of toxins, which may elicit devastating effects on marine life. Diarrhetic Shellfish Poisoning (DSP) is a specific type of food poisoning, characterized by severe gastrointestinal illness due to the ingestion of filter feeding bivalves contaminated with a specific suite of toxins such as okadaic acid (OA) and dinophysistoxins (DTXs). OA and DTXs are lipophilic and heat-stable compounds that frequently accumulate in bivalve mollusks along European coasts. It is established that organisms such as bivalves accumulate these toxins in their tissues, mostly in the digestive gland, through their filter feeding behavior acting therefore as a vectors for other organisms such as planktivorous fish. Here, for the first time, the time course of accumulation and elimination of Diarrhetic shellfish toxins (DSTs) in juveniles of Zebra seabream (Diplodus cervinus) was assessed during an experimental period of 15 days. It was shown that fish present a high excretion rate and low toxin conversion, in fact no other compounds except for DTX-1 were found. Then fish aerobic metabolism and swimming performance were investigated, exposing individuals to OA group of toxins via dietary route during 3 days, after which fish were challenged with increasing swimming velocity trials using a swim tunnel respirometer. Results show that OA impaired on metabolic performance, assessed both during the standard metabolic rate (SMR) and during the maximum metabolic rate (MMR) as an oxygen consumption increment. Moreover, from critical swimming speed (Ucrit) analysis, significant differences among the two tested groups were observed. In conclusion, these studies show that fish can act temporary as a vector and, although a high elimination rate was found, at the same time toxins ingestion was able to impair their fitness.