Every time there is a red tide warning, I always hear the news like this:
A red tide alert is raised in blank area. All the residents are advised to refrain from eating shellfish -mussels and oysters!
Red tide is really scary. I already heard several news about persons who died from eating contaminated tahong. The least damage one could get is gastrointestinal pain.
Red tide is cause by harmful algal blooms or the rapid population increase of toxin producing algae. The common toxin reported by Bureau of Fisheries and Aquatic Resources (BFAR) is the saxitoxin – a nuerotoxin produced by some species of marine dinoflagellates that can cause paralytic shellfish poisoning (PSP). Another species reported by Centers for Disease Control and Prevention is the Krenia brevis. This specie produces a powerful brevetoxins.
In general, here are types of poisoning one could suffer (BFAR):
1) Paralytic Shellfish Poisoning (PSP)
2) Diarrhetic Shellfish Poisoning (DSP)
3) Amnesic Shellfish Poisoning (ASP) – causing partial memory loss.
4) Ciguatera Fish Poisong – Causing nausea, vomiting, and diarrhea, usually followed by neurological symptoms such as headaches, muscle aches, paresthesia, numbness, ataxia, and hallucinations [wikipedia].
You might be wondering why the shellfish (tahong, talaba) are the most affected. Why do other fish are not included in red tide warnings?
Tahong and talaba are sedentary organisms. They have no ability to move from one place to another. They cling to underwater bamboo poles. Feeding is done by opening their shell and filtering the water the that cross their path. Concentrating harmful amounts of toxins is accidentally done by this manner.
Other fish are also affected by toxins but they are choosy regarding what they eat and can avoid harmful part of the sea.
The means to tell if tahong has red tide are:
1) Television news.
2) Visiting the BFAR website. They are monitoring Philippine coastal areas regularly and publishing the results on their web.
Before cooking tahong, rinse it with tap water and throw away all the open shells – those are probably bad. Its not a measure to avoid red tide however.