Unit-9_Toxic factors in Fish

NUTR*4510 Toxicology, Nutrition & Food

  • Unit 9: Toxic Factors in Fish Products

Fish Poisoning Documentation

  • Early documentation shows symptoms of neurotoxicity associated with fish poisoning.

Seafood Toxins

1. Ciguatoxin

  • Produced by phytoplankton (G. toxicus) around reefs.

  • Bioaccumulates in large reef fish (barracuda, grouper, snapper).

  • Physical Properties:

    • Lipid soluble.

    • Heat stable (does not degrade with cooking).

  • Causes "ciguatera," the most common fish-borne illness worldwide.

  • Metabolism:

    • Phase I via CYP3A4 and CYP2 family (2B9, 2B10, 2J9, 2J11, 2J13) within first 24 hours.

    • After 24 hours, metabolized by CYP4 family (4A1, 4A10, 4A14).

    • Phase II via glutathione conjugation (catalyzed by GST enzymes).

2. Saxitoxin

  • Produced by phytoplankton (G. dinoflagella).

  • Bioconcentrated by filter-feeding bivalve mollusks (mussels, clams, oysters, scallops).

  • Physical Properties:

    • Water soluble.

    • Heat stable.

  • Causes "paralytic shellfish poisoning."

  • Not metabolized in mammals; intact structure detected in liver, spleen, and brain.

3. Tetrodotoxin

  • Likely produced by bacteria, bioconcentrated by hosts (e.g., puffer fish).

  • Physical Properties:

    • Water soluble.

    • Heat stable.

  • Causes "puffer fish poisoning"; lethal at 1-4 mg.

  • Symptoms of cardiovascular and respiratory failure can appear in ~17 minutes.

  • Metabolism pathway in humans remains undetermined; differs from marine species.

Toxicity and Health Effects

  • Seafood toxins have similar adverse health effects but vary in onset speed (e.g., tetrodotoxin has rapid effects).

  • Symptoms include:

    • Hyperesthesia (increased sensitivity to stimulation).

    • Paresthesia (tingling/numbness).

    • Sensation of floating.

    • Headaches.

    • Ataxia (poor muscle control).

    • Vertigo.

    • Respiratory failure from diaphragm paralysis.

    • Cardiovascular impacts: hypotension, pulmonary edema.

    • Gastrointestinal effects: abdominal pain, diarrhea, vomiting.

Mechanism of Action of Seafood Toxins

  • Nerve signal transmission occurs via action potentials (electrical changes across neuron membranes).

  • Ciguatoxin:

    • Enhances depolarization and delays nerve signal propagation.

  • Saxitoxin and Tetrodotoxin:

    • Prevent depolarization, inhibiting nerve signal propagation.

    • Process involves voltage-gated sodium channels opening (Na+ influx) then potassium channels (K+ efflux) to reset the neuron.

Metabolism of Fish Toxins

  • Ciguatoxin:

    • Metabolized primarily via CYP enzymes into phase I and II metabolites.

  • Saxitoxin:

    • Intact form remains in mammals; no known metabolism.

  • Tetrodotoxin:

    • Metabolism pathway is still under research; believed to differ in humans versus marine hosts.

Sport Fish Toxins/Xenobiotics (Local Freshwater Fish)

Characteristics of Toxins

  • Lipophilic, chemically stable, and metabolically resistant.

  • High bioavailability; low toxicity at intermediate food chain levels.

Conditions Favoring Bioaccumulation

  1. Proximity to contamination sites.

  2. Increasing age and size of fish.

  3. Higher lipid content facilitating storage of toxins.

  4. Higher dietary positions in the food chain.

Common Sport Fish Toxins in the Great Lakes

  • PCBs, Mercury (methyl-mercury), Dioxins, and Furans recognized for persistence and toxicity in fish.

Monitoring Common Contaminants in Ontario Fresh Water Fish

  • Mercury:

    • Converted to methylmercury; high levels in top predators (e.g., Walleye, Pike).

  • PCBs:

    • Banned but persist in the environment; accumulate in aquatic ecosystems.

  • Dioxins/Furans:

    • Industrial by-products; significant bioaccumulation in fatty fish.

  • Toxaphene, PFAS, Selenium, Arsenic, PBDEs:

    • Various harmful impacts; persistence in the environment and fish tissue.

Bioaccumulation Up the Food Chain

  • Notable increases in toxin concentration as one moves up the aquatic food chain, presenting risks for higher trophic levels.

Toxins in Sport Fish/Great Lake Fish Species

1. Polychlorinated Biphenyls (PCBs)

  • Banned yet still prevalent in the environment; linked to significant health effects in humans.

2. Dioxins

  • Carcinogenic effects; accumulate through industrial contamination.

3. Methyl-mercury

  • Naturally occurring; detrimental cognitive and sensory effects, especially in developing fetuses.

Consumption Guidelines

  • Recommendations on size and frequency of fish consumption tailored for vulnerable populations (children, pregnant women).

Interpreting Fish Servings

  • Definition of fish meal servings based on weight, with standard measurements to limit consumption based on health guidelines.