cool, I like this juxtaposition. I would suggest a small grammatical change. I get the image of a couple fishing on the ocean, they've caught their last fish, maybe they were swimming earlier too, and they kiss, tasting each other's salty lips (maybe to celebrate that last catch.) So to that effect, I would get rid of the word "tasting" which should be implied/understood. grammatically it kind of reads like the the last fish is tasting salty lips. taking away the verb separates the first line from the last two as its own separate, juxtaposed image. so; salty lips/ the last fish/ flops on the deck gives a nice image. hey, it can go both ways too, really, with just one person and his own salty lips, this way it's up to the reader just to have that image of salty lips (the flavor on the lips implies tasting already). I encourage getting rid of redundancy in haiku to have the most powerful image. Ok, lengthy run-on analysis over & out ;) great haiku!

i like the imagery as it is: simple and clean. don't change a thing.