Fish due to variety and types.
Just because you can prepare multiple type of beef or Pork or chicken dishes at the base it is still the same cow, pig or chicken.
You could arguably take one kind of fish and also make as many originally new dishes with it and use many different cuts. Now expand that to hundreds or thousands of different kinds of fish from Ocean, to lake, to river, with so much difference in the 'base animal' you are eating and anyone thinking a single species of land animal has more variety is greatly mistaken.
The proper comparison would be all the forms of fish (or water animals) versus all the species of land animals.