The Fish, the Snake, and the Pig
As the Ben Yehoyada explains:ת"ר שלשה כל זמן שמזקינין מוסיפין גבורה ואלו הן דג ונחש וחזירOur rabbis taught in a Beraita: there are 3 things that get stronger with age: a fish, a snake, and a pig.
It appears to me, with Hashem's help, that the reason that HKB"H did so with only these creatures is because there are 3 nations in the world whose lineage remains in the world more than the 70 nations. They are: Israel, Yishmael, and Edom. This is because Sanheriv mixed around the other nations and they have no known name nowadays.
Therefore, He did this with the fish which is a Kosher species - in that the more it ages, the stronger it gets - corresponding to Israel, who is compared to fish in that the more the nation of Israel ages, its strength increases relative to itself as they have glory in this.
And He did this with a snake, which is a non-Kosher species, corresponding to the nation of [Yishmael], as it says in Ra'ya Mehemna in Pinhas p.
276 that "Snake" is appointed over [the nation of Yishmael] and he is "Ra-hav" ...
And He did this with a pig, which is a non-Kosher species, corresponding to Edom, which is Esav, as it says in the book Megaleh Amukot, Ofan 147 that Esav is compared to a pig, as it says: "The boar out of the wood doth ravage it".