I'm hesitant at the idea of pescetarianism. If larger animals are more sentient, then fish don't matter much, and that's a good idea. But some people argue otherwise. If there's a significant chance that fish are as sentient as anything else, eating only fish is a terrible idea.
While I was adjusting to vegetarianism, I tried to eat mid-sized animals, so it wouldn't be terrible either way.
Perhaps beef-only could be an alternative to fish-only as a stepping stone? I think I remember beef getting better ratings than most other things in some articles comparing utility of eating animals with the assumption that all creatures suffer equally. (Pigs are smarter than cows, I think, but I'm not sure if you were considering them mid-size or large.)
Neal Stephenson's The Diamond Age takes place several decades in the future and this conversation is looking back on the present day:
I'm not sure if I agree with this characterization of the current political climate; in any case, that's not the point I'm interested in. I'm also not interested in moral relativism.
But the passage does point out a flaw which I recognize in myself: a preference for consistency over actually doing the right thing. I place a lot of stock--as I think many here do--on self-consistency. After all, clearly any moral code which is inconsistent is wrong. But dismissing a moral code for inconsistency or a person for hypocrisy is lazy. Morality is hard. It's easy to get a warm glow from the nice self-consistency of your own principles and mistake this for actually being right.
Placing too much emphasis on consistency led me to at least one embarrassing failure. I decided that no one who ate meat could be taken seriously when discussing animal rights: killing animals because they taste good seems completely inconsistent with placing any value on their lives. Furthermore, I myself ignored the whole concept of animal rights because I eat meat, so that it would be inconsistent for me to assign animals any rights. Consistency between my moral principles and my actions--not being a hypocrite--was more important to me than actually figuring out what the correct moral principles were.
To generalize: holding high moral ideals is going to produce cognitive dissonance when you are not able to live up to those ideals. It is always tempting--for me at least--to resolve this dissonance by backing down from those high ideals. An alternative we might try is to be more comfortable with hypocrisy.
Related: Self-deception: Hypocrisy or Akrasia?