Reference for Chullin 3:7
וּבַחֲגָבִים, כֹּל שֶׁיֶּשׁ לוֹ אַרְבַּע רַגְלַיִם, וְאַרְבַּע כְּנָפַיִם, וְקַרְסֻלַּיִם, וּכְנָפָיו חוֹפִין אֶת רֻבּוֹ. רַבִּי יוֹסֵי אוֹמֵר, וּשְׁמוֹ חָגָב. וּבַדָּגִים, כֹּל שֶׁיֶּשׁ לוֹ סְנַפִּיר וְקַשְׂקָשֶׂת. רַבִּי יְהוּדָה אוֹמֵר, שְׁנֵי קַשְׂקַשִּׂין וּסְנַפִּיר אֶחָד. וְאֵלּוּ הֵן קַשְׂקַשִּׂין, הַקְּבוּעִין בּוֹ. וּסְנַפִּירִין, הַפּוֹרֵחַ בָּהֶן:
Of locusts, all the species are clean which have four feet, four wings, and four leaping legs, and whose wings cover the greatest part of its body; R. Jehudah saith, "Only then when they are called by the name חגב." Of fishes, are clean, those furnished with fins and scales; R. Jehudah saith, "When they have at least two scales and one fin." Scales are attached to the body of the fish, and fins are the organs by which it moves through the water.