For my daughters 2 yr. birthday party, we did a fish theme.  On the front door I made a sign that said "Something Fishies Goin On" and had a string with a paper clip tied to the end(bent to look like a hook). On the paperclip hook I put a gummy worm. We cut out fish out of construction paper and glued it to the sign (could also use fish printed out from crayola.com). We also put green and blue streamers from the ceiling with blue, green and orange construction paper fish or a blue/white balloon (for bubbles)hanging from each streamer.  For the table we used a blue table cloth with a fish net overtop. Again, we stuck more construction paper fish in the net.  We also had a big inflatible shark which we blew up and put in the corner.  I put kid's butterfly nets/critter nets/beach towels with fish/fish swimming tubes, etc. hanging from places where I usually have pictures hanging.  For the meal we had fish fillets, shell macaroni salad, tatertots, ocean water punch (blue), and the typical blue jello with swedish fish swimming around.  I made the jello in a fish bowl to look more real (it was so real one kid wouldn't even eat it :-) For the cake I covered a big piece of card board (2'x3')first with tin foil and then with blue saran wrap (to look like water).  I made fish out of Rice Krispy bars (rather then put in a pan, just wet hands and shape like fish - can make variety of sizes). We used a mini M&M for the eye and a piece of string licorice for the mouths. I also made rice krispy bar octupus (Rice Krispy ball with gummy worms for the tentacles).  I baked a regular 9x13 cake, frosted, then covered with graham cracker crumbs (sand) to look like an island.  I put this on the piece of card board surrounded by more blue saran wrap to look like water coming up to the island. I frosted teddy grahams with gel frosting (various colors) to have on swimming suits and sunglasses.  On the island some where laying out on beach towels (fruit by the foot - cut to towel size for each bear).  Some swimming in innertubes (lifesavers) and some fishing (pretzel stick with string licorice tied to it). I used drink umbrellas for beach umbrellas.  I made sail boats out of twinkies with a fruit roll-up sail and a stick pretzel to hold the sail on.  I also put a teddy graham bear riding on each sailboat. All these things were arranged on the card board to look like an ocean/island scene. The kids looked at the cake forever, finding all the neat little things. We have a variety of ages from 2 to 9 so for games we played the usual fishing game.  We have an open stair case in which we covered with a blue table cloth. Earlier during the week my kids and I printed out pictures of fish and ocean creatures (off the internet-Crayola.com). We painted and colored them and glued them to the table cloth to make it look like an aquarium.  We gave prizes like Livesavers (our earlier innertubes), Goldfish crackers, gummy shark bites, and water guns for the fish game. We also played the eat the worm game in which we clothes-pinned a gummy worm to a fishing pole and each kid had to try to eat it (I first tied each worm to a string licorice, then they could eat the whole thing and I didn't have to worry about germs on the clothespin).  For the final game I wove a piece of string through-out the house and one at a time had to find where it led.  It led to a fish bowl with fish in it in which they each got to take one home (check with the parents if this is ok).  They each got to catch their own fish out of the bowl with a net (they took them home in a Rubbermaid Takealongs with a lid).  This was a fun party - full of action.  Everyone, even the parents had a good time.