answer the three questions please 1) What is meant by a negative feedback loop regarding the regulation of triiodothyron

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answer the three questions please
1) What is meant by a negative feedback loop regarding the
regulation of triiodothyronine and thyroxine blood levels in
fish?
2) Explain how environmental stimuli initiate the release
of triiodothyronine and thyroxine from thyroid gland tissue in
fishes.
3) Do you think fishes originated in the marine or
freshwater environment? Explain your answer.