They are not emotions. They are instinctual reactions. They cannot be tempered or subdued like emotions.
When fish come up to the surface towards an owners hand it’s because they think are being fed.
Of course, I could be wrong. We could all be the same life-force just in a different shape...
Fish are incapable of emotion and therefore do not grieve. You could replace the ex-fish with a carrot stick and the surviving fish would know no different.