While fish _will_ nibble the roots of W.Hyacinth, are you sure that was the
cause? Hyacinths often fail to thrive when there's a potassium (iirc - I
always get my potassium/phosphorus mixed up) deficiency. They go yellow,
_then_ they lose their roots.
How do I stop this? I feed the fish everyday during the summer months .

If it is the fish, netting around the roots helps.

I didn't add any fertilizer to the pond for the hyacinth. It was my
first year last year with these plants. Should I give them any
treatment other than throwing them in.

Get then to a hydroponics.com franchise. Use potassium sulphate
or potassium nitrate (if you're nitrates are low). And use the
iron+trace mix. These are whan you're deficient in.

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