The difference between forgetting fish and ingratitude lies in the differences in explanation, usage and part of speech;

1, different interpretations

Forgetting fish: catching a fish and forgetting it is a metaphor for forgetting what you rely on after success. Sasakawa: Bamboo for fishing.

Ungrateful: Forgetting the benefits of others for yourself, but doing something sorry for others. Grace: love, negative: disobedience, righteousness: friendliness, kindness.

2. Different usages

Forgetting fish: Used with verbs as predicate, object and attribute, which is derogatory.

Ungrateful: United, as predicate and attribute, derogatory, used to condemn.

3. Different parts of speech

Forget fish: it can be used as a noun in a sentence.

Ungrateful: You can be a gerund and a predicate verb in a sentence.