As others have allready stated , April is early for tuna, Yellow Tail, ect. What they have failed to mention is our fabulous inshore fishing. Both Mission and San Diego Bays can provide , if you know where and when, awsome cathes of Barred Sand Bass, Spotted bay bass, Calico bass, Bonita, barracuda, ocasional White Sea Bass, croaker (3-4 different species), corvina, corbina, BONEFISH !, HALIBUT, GIANT BAT RAYS, several species of sharks. Just a partial list.
As far as knowing where when, and how, there is none finer than Captain Bill Shaefer. He is a local guide and sports writer specializing in San Diego Bay And the local costal fishing. He has one of the finest bay boats you will ever see, has all the very high quality tackle you'll need, and knows how to put you on to the fish. His rates are very reasonable at $250 day. The education you will recieve from one day of fishing with Bill is worth that alone. BTW , I have no affiliation with Captain Bill. Here is his link
http://www.sdfishinguide.com/ also check out sdfish.com Have fun and hope your rod gets bent plenty, Ken