I have about a nine inch african pike. He is about 1 year old. I had been feeding him frozen silversides but in the last week or so he hasn't eaten them. I did get him to eat an earthworm. Other than not eating, he is swimming and seems okay. Would there be any reson for the change? Also water parameters are nitrites: 0, nitrates: ~20ppm. He is in a 65 gal(4' long by 1.5' wide) tank by himself.