Do fish lay eggs underwater?
Most fish release thousands of eggs, scattering them in the water where the male fish fertilize them. The eggs develop and hatch into larvae (baby fish) without any help from the parents.
As the chance of fertilization is nature dependant i.e it depends on the movement of water for the sperm to come in contact with the egg. Thus the fish and frog produce a huge number of eggs each year to overcome the chance factor(sperm to come in contact with egg) and produce offsprings.
fish lays thousands of eggs because some of them are eaten by big animals and some of them don't get enough Oxygen and some more things that they can't grow , So fish has to lay many Eggs so that so of them becomes a new one.
In addition, the eggs that were exposed to air developed faster than the aquatic eggs, with 95% reaching a stage where they could hatch after 15 days, compared with 45% in aquatic eggs.
The platypus is a remarkable mammal found only in Australia.
The platypus is a duck-billed, beaver-tailed, otter-footed, egg-laying aquatic creature native to Australia.
Frogs, toads, and other amphibians lay their eggs in water.
Until his offspring hatch, the male diligently tends to the nest (see image), protecting it from predators and fanning his tail to aerate the eggs. And during this period, the male can't leave his nest unguarded. Thus, he resorts to eating some of its contents to survive.
But even under the best conditions, at least 70% of newly hatched fish still die. For example, the Tel Aviv researchers found that at Har Dag, a veteran fish farm in Eilat, typically 250,000 larvae survive from one million hatched eggs.
Egg buoyancy. The major fractions of marine fish eggs are pelagic or mesopelagic implying that they float above the seabed.
Fish reproduce by bearing live young or by laying eggs. Livebearers give birth to fully formed and functional young called fry. The eggs are fertilized and hatch within the female.
Can shark lay eggs?
There are over 500 species of shark living in waters around the world and the majority give birth to live young. The remainder are oviparous, meaning they lay eggs. Around 40 to 50 different shark species live permanently in or regularly visit the waters surrounding Britain.
The female will lay the eggs and they will be dispersed through the water where the male will fertilize them. But some fish engage in a form of intercourse or a mating ritual. There are also types of fish that can fertilize themselves. The best hypothesis for mermaid reproduction is that they mate in the same fashion.

Preserving eggs utilizing the water glassing method allows farm-fresh eggs to remain fresh between one year to 18 months. However, there are individuals who state their eggs remain edible for up to two years in the preserving liquid. The method of water glassing eggs has been practiced since the early 1800s.
The best kept secret in determining an egg's freshness is to see if it sinks in water. To try the egg water test, simply fill a glass or bowl with cold water and submerge the eggs. If the eggs sink to the bottom and lay flat on their side, they're still fresh.
Water and warm temperatures are a breeding ground for salmonella, meaning the water on the eggshell exposes the egg to contamination. Even if the room-temperature eggs don't have condensation on them, bacteria can still contaminate them through the thinned shell.
In the Amazon, splash tetras stage a leaping contest. They jump out of the water to lay their eggs on leaves.
Egg buoyancy. The major fractions of marine fish eggs are pelagic or mesopelagic implying that they float above the seabed.
Fish reproduction methods vary, but most types of fish lay eggs. The female fish lays unfertilized eggs in water nests or builds a safe area for them, then the male fertilizes these eggs; that is, the eggs are fertilized and mature outside the mother's body.
Eggs incubating higher in the intertidal spend more time out of water than their counterparts in the low intertidal or submerged in subtidal spots. While these soon-to-be-fish out of water may seem in peril, Frommel says they can survive these conditions for extended periods of time, even up to 24 hours.