An Unfortunate Amalgamation of Mammal and Fish

I was called the product of a pig and an ass.

And it had to be admitted, I was notoriously crass.

My daily meal was unfresh bass.

So, belching a lot, I did without a lass.

It was, you see, a surfeit of gas.

I would follow any herd to where they would mass.

But the herd would part, to let me pass...