על החוקים לפרטיהם, ספר ד כ׳On the Special Laws, Book IV 20
א׳
1[110] After laying down these limitations for the land animals he proceeds to describe such creatures of the water as are clean for eating. These too he indicates by two distinguishing marks, fins and scales; all that lack either or both he dismisses and repudiates. I must state the reason for this which is appropriate enough.
ב׳
2[111] Any that fail to possess both or one of these marks are swept away by the current unable to resist the force of the stream; those who possess both throw it aside, front and stem it and pertinaciously exercise themselves against the antagonist with an invincible ardour and audacity. When they are pushed they push back, when pursued they hasten to assail, where their passage is hampered they open up broad roads and obtain easy thoroughfares.
ג׳
3[112] These two kinds of fish are symbolical, the first of a pleasure-loving soul, the latter of one to which endurance and self-control are dear. For the road that leads to pleasure is downhill and very easy, with the result that one does not walk but is dragged along; the other which leads to self-control is uphill, toil-some no doubt but profitable exceedingly. The one carries us away, forced lower and lower as it drives us down its steep incline, till it flings us off on to the level ground at its foot; the other leads heavenwards the immortal who have not fainted on the way and have had the strength to endure the roughness of the hard ascent.