Anybody would want to have sex with a butterfly. You'd have to be really drunk to have sex with a roach. In fact, that is just how roaches do it. They sit around under the refrigerator and swill cheap wine until their standards get really low, then they have drunken, tawdry sex. The female immediately lays 40 billion eggs which hatch the next day, but by that time the parents have moved to another area of the kitchen and changed their names, so the children have nobody to love and care for them, and they pass the time eating little rolled-up balls of ketchup and floor dirt, and before long they, too, turn to liquor, and the cycle of life repeats.
Fish are completely different.
Most fish live underwater, which is a terrible place to have sex because virtually anywhere you lie down there will be stinging crabs and large quantities of little fish staring at you with buggy little eyes. So generally when two fish want to have sex, they swim around and around for hours, looking for someplace to go, until finally the female gets really tired and has a terrible headache, and she just dumps her eggs right on the sand and swims away. Then the male, driven by some timeless, noble instinct for survival, eats the eggs. So the truth is that fish don't reproduce at all, but there are so many of them that it doesn't make any difference. The only exception is the shark.