sacs onto stones or branches and the male later hovers over the eggs to release the sperm to them. Males are seen to be very protective over the eggs and may continue to hover over the eggs after sperm release to decrease sperm competition. In some cases, males may even latch onto the females while they lay their eggs to ensure that they fertilize them first. Other times there may be numerous males surrounding a single sac of eggs, creating scramble competition. Cryptobranchid sperm is seen to have higher longevity. This is about 600 times greater than in freshwater fish, but not even close to as high as anurans. Fish Salmon, cod, trout, and char are all examples of the fish that externally fertilize. The females release roe (an egg mass) and the males release milt (seminal fluid containing sperm) into the water, where they diffuse together and fertilize. On top of the sperm locating the oocyte and penetrating the gel layer, it must also infiltrate the mycropyle. If there is turbulent water or even in open, calm water, the closer fish that releases sperm has the higher chance of fertilizing the eggs. If sperm is released too early, it can become too dilute or die before it ever reaches the eggs. If sperm is released too late, there is a higher chance that a different fish's sperm has already reached the eggs. Also, the faster and more numerous the sperm, the better. There are instances where males will create habitats in an attempt to monopolize females and increase their chance of fertilizing eggs. Fishes can be iteroparous, and spawn more than once, but there are some who only spawn once before death, known as semelparous. Within iteroparous fish, they usually give no parental care with external fertilization. The sperm present in male fish are immotile while in testes and in seminal fluid, and the fertilization environment determines when the sperm become motile. In salmon, a decrease of potassium in fresh water will initiate the motility of the sperm. A decrease in osmolality after spawning in fresh water makes a cyprinid fish's sperm motile. See also Fertilization References Sexual reproduction Reproduction in animals