Seriously, don't use the word OP so fast, I think with 2 different quanta cost for 6 dmg, this card is quite balanced.
When evaluating this card I was also comparing this card to the others, but when i mentioned the 
cost, it was based on the fact that
Flesh Recluse 
= 6 damage
Giant Frog 
= 5 damage
But since flying fish requires 1 air quanta every turn, it seems fair to keep it at one quantum cost
As was mentioned above me, you've left buffs out of your calculations. Also the creatures you've chosen for comparison aren't quite appropriate.
For Giant Frog, you'll note that across the board
creatures always have better stats for the cost than comparable creatures in other elements. This is one of the strengths of the
element and making creatures in other elements comparable to
creatures would be unbalancing.
For Flesh Recluse, you'll note that the damage versus initial cost is much better for the fish, and the fish is easier to buff. In addition, the dive ability makes it so that if you are low on quanta you can just skip on diving it for a turn, and it still does 3 damage, which is still better than any other 1 quanta cost creature that I know of.
