Not everything we do requires that we derive pleasure out of it. For example, not too many people get great pleasure out of breathing, yet we do so anyway. it can be hard to sometimes put a line between pleasure and some sort of biological instinct but we can look at some breeding practices and see that not all creatures find it "pleasurable".
- Many animals die right after mating. Reproducing takes a lot of energy, so there can be an advantage if a creature can give everything it's got to the next generation. Salmon and most octopuses fall into that class.
- Some animals allow themselves to be consumed by there mates. Spiders are an excellent example. A nitrous snack for the female can ensure that she has enough energy to lay her eggs. Plus as long as the female is munching on the male, she's not mating with someone else.
- For the title of least pleasurable mating practice, look no further than the male grouper fish. Male grouper fish are born immature and never fully developer. They can't even eat. Their sole task is to locate a female group who is 30 to 100 times his size and bite her and hold on. Soon their jaws and mouths disappear and blend into the female. Their body organs deteriorate, and all that's left of the male is his reproductive organs hanging off The female's body.
When scientists first started investigating groupers, they realized all they saw were females and never a male. And all the females had these "tumors" all over them. Only later did they understand that those tumors were the remains of various males.
Scientists speculate that this mating practiced probably developed because groupers are not that common in the deep sea. It would be highly unlikely for a male and female to meet up when the female is breeding. Therefore, a male becomes part of the female and his sperm are there whenever the female is ready to breed.