Oral sex is practiced by many people also as a contraceptive measure. Not few still believe that sperm would get through the digestive system to fertilize the eager egg. But sperms can be more varied and act weirder than we can imagine. And if there are bug males who fertilize the female by stabbing her into the abdomen and the sperm cells make their way to the eggs through the blood stream, you should also know that there are species were fertilization occurs through oral sex!

There are some catfishes in which sperm passes through the female's digestive tract to the eggs, the sperm drinking type of fertilization, ending into an external fertilization. These sperm drinking species belong to two Neotropical families of catfish: driftwood catfishes (Auchenipteridae family) inhabiting rivers from Panama to Argentina, and armored catfish (Callichthyidae family), from South America and Panama, popular aquarium species.

The male of this species has a pair of seminal vesicles (absent in most other fish species), and they release the sperm in the form of discrete bundles (spermatozeugmata).

The main function of the seminal vesicles is the secretion of mucin, a sticky combination of sugars and proteins, which has the role to protect the sperm while passing through the female gut.

During the courtship, a male shows its abdomen to the female. Before expelling the eggs, the female attaches her mouth to the male's genital opening (there is no penis in any known catfish species!), and directly sucks his sperm.

The sperm cells go unharmed through the female's gut and are released together with the eggs into the "pouch" made by her pelvic fins (thus, in the end, fertilization is external, not inside the female's body). This way, the eggs get in contact with fresh non-dispersed sperm in an enclosed space, ensuring a more effective insemination, not disturbed by the water flow. Scientists discovered this type of fertilization in 1994.