Most male fish spread their sperm over female eggs just because they have come into proximity with the eggs. The female may even have departed, and there is no contact with her. So what is it about just seeing (or tasting?) the female eggs spread out before him that induces the male fish to produce sperm? Does he experience something like sexual excitation or is his sperm spreading just a deliberate act induced by seeing the eggs?

Most male fish spread their sperm over female eggs just because they have come into proximity with the eggs. The female may even have departed, and there is no contact with her. So what is it about just seeing (or tasting?) the female eggs spread out before him that induces the male fish to produce sperm? Does he experience something like sexual excitation or is his sperm spreading just a deliberate act induced by seeing the eggs?

 

In the UK the male and female fish do it together by bring their reproductive parts in close proximity to each other in stillwaters and the male is somewhat in front in running waters as far as I have observed...it's a simultaneous action. I appreciate things may be different in other parts of the world.

Fish breeding behavior is quite variable between different species and groups. For some, the spread of eggs and sperm is almost random, while other species have courtship displays and activities, build nests, and care for their young. There are even several groups that fertilize eggs internally and produce live young (I have caught surfperch females that squirted out a dozen live babies after hauling them up on the beach). There are studies that demonstrate that visual cues are important (e.g. sticklebacks get turned on by pornographic videos of mating pairs) while touch and lateral line stimulation is very important for others (e.g. Astyanax fasciatus, Mexican blind cave characins, have a side by side flutter that coordinates ejection of sperm and eggs). By far the most studied stimulation is hormonal or endocrine products related to the generation of mature sperm or eggs that mediate communication between males and females for coordinating breeding activities. If it were a little easier, fish watching would be right up there with bird watching. SM