• cooking shellfish or fish to destroy the toxins;
• watching shellfish or fish for an extended time to see if they behave strangely;
• a change in color when a silver coin is placed on a fish;
• eating shellfish caught in months with the letter "R";
• if the water is discolored it means biotoxins are present;
• eating shellfish or fish caught in specific locations is always safe.

The only way to tell if fish or shellfish contain biotoxins is through laboratory testing. Discolored water from an algal bloom does not necessarily mean the blooming algae produce biotoxins.

	Red Tide Hotlines
	Most states have "red tide" hotlines or Web pages which recreational fishers can call and receive up-to-date information about the safety of particular beaches.

Conversely, some harmful algal blooms (HABs), such as those that produce saxitoxin, which causes life-threatening paralytic shellfish poisoning (PSP), do not discolor the water. So far, the best way to avoid accidental poisonings from toxic shellfish has been for local and regional authorities to closely monitor algal blooms and test coastal waters for biotoxin concentrations. When they reach dangerous levels, authorities should post public notices and stop shellfish harvesting until there is no longer any danger. The coastal states and provinces of North America have developed monitoring programs that warn the public of biotoxin dangers. Canadian authorities, for example, have monitored the water column around Prince Edward Island for the phytoplankton and the biotoxin it produces that caused numerous cases of amnesic shellfish poisoning (ASP), including some deaths, in 1987. When concentrations of domoic acid reach 20 µg/g of shellfish meat, harvesting of area shellfish is closed. In addition, commercial shellfish operations must send frequent samples to testing centers and are in communication with appropriate health agencies to ensure the safety of their products.

However, not all countries have thorough monitoring systems: with the international transport and sale of seafood there is always a possibility of falling victim to a biotoxin. For the individual consumer, the best advice is to be prudent and to only buy or eat shellfish or fish at reputable establishments. Biotoxins tend to accumulate in the viscera, or guts, of shellfish and fish, making these parts especially dangerous. Muscle tissue, such as the adductor muscle of scallops, is often toxin free. Some tropical reef fish and predators to be especially careful about include the following:

• Grouper
• Red snapper
• Red bass
• Barracuda
• Moray eel
• Parrotfish
• Chinaman fish
• Coral trout
• Narrow-barred Spanish mackerel
  

Toxin treatments
Treatments vary depending on the type of biotoxin the victim has ingested. Since death can occur within 24 hours in the case of paralytic shellfish poisoning (PSP), which is caused by a variety of saxitoxins, it is important to seek medical attention as soon as the victim starts to show signs of sickness, such as a tingling or numbness around the mouth or face and neck. Once under medical care, patients should be put on ventilators to aid respiration, with drugs like benzedrine also aiding respiration and decreasing recovery time. Treatment for another potentially life-threatening biotoxin, domoic acid, which is responsible for amnesic shellfish poisoning (ASP), is also primarily symptomatic. Examples include using IV diazepam and phenobarbital to reduce seizures.

Medical treatment for ciguatera poisoning, which is estimated to account for about half of biotoxin poisoning incidents, mostly focuses on the symptoms. Vitamins, antihistamines, anticholinesterases, steroids and tricyclic antidepressants have been tried with limited results. Gut emptying and decontamination with charcoal is sometimes tried, but severe ongoing vomiting and diarrhea can prevent this. Opiates and barbiturates should be avoided since they may cause hypotension, and opiates may interact with maitotoxin, one of the biotoxins responsible for ciguatera poisoning. If intervention occurs with a day or two of ingestion of ciguatoxic fish, treatment with mannitol can be very effective and thus should be promulgated as an important therapeutic step to be followed in all CFP cases. The treatment involves intravenous infusion of 20 percent mannitol (1 g/kg at a rate of 500 mL per hour) over 30 minutes, "piggy-backed" on an intravenous infusion at 30 mL per hour of 5 percent dextrose in saline solution. Mannitol treatment is most effective if given within 48 hours of exposure, but can still be moderately effective if given 3 to 14 days after exposure.

When the brevetoxins responsible for neurotoxic shellfish poisoning (NSP) are aerosolized, filter masks or moving to an air-conditioned room have been shown to help ease the asthmatic symptoms that these toxins cause. These toxins come from the phytoplankton responsible for Florida's "red tides," which discolor the water, cause beach closures and massive fish kills.