Manava Dharmashastra 5.15

5.15

pūrvasya matsyapratiṣedhavidherarthavādo'yam | yatsambandhimāṃsaṃ yo'śnāti sa tanmāṃsasambandhinyā'śanakriyayā vyapadiśyate | yathā sarpādau nakulaḥ, mārjāro mūṣakādaḥ, ityādi | yastu matsyādaḥ sa sarvamāṃsāśī bhavati | gomāṃsāda ityapi vyapadeṣṭuṃ yuktaḥ | ato nindātiśayānmatsyānvivarjayet |

He who eats the flesh of an animal, is called the ‘eater of its flesh’; he who eats fish is the ‘eater of all kinds of flesh’; hence one shall avoid fish.—(15).

Medhātithi’s commentary (manubhāṣya):
This is a commendatory supplement to the foregoing prohibition of fish.

When one eats the flesh of an animal, he comes to be described as connected with the act of eating that animal; e.g., the mungoose is called ‘serpent-eater’, the cat ‘rat-eater’ and so forth. He who eats fish eats all kinds of flesh; it would be right to speak of him as a ‘beef-eater’ also.

Hence, by reason of the possibility of this calumny, one should avoid fish.—(15).