* External fertilization: Fish eggs are fertilized externally, meaning the sperm and egg meet outside the female's body. This makes it much less efficient than internal fertilization, where the sperm directly enters the egg. As a result, fish need to produce many eggs to ensure some survive.
* High mortality rate: Many fish eggs are eaten by predators, or never get fertilized. The open environment and lack of parental care makes young fish highly vulnerable. Producing many eggs increases the chances that some will survive to adulthood.
* Lack of parental care: Most fish species provide little to no parental care for their young. The eggs are left to develop on their own, and the fry (young fish) must fend for themselves from the moment they hatch.
* Environmental factors: The aquatic environment can be unpredictable. Water currents, temperature fluctuations, and the availability of food all contribute to the high mortality rates among fish eggs and larvae. Producing more eggs increases the chances that some will survive in these challenging conditions.
* Evolutionary pressure: Over generations, fish species that produced more eggs were more likely to leave offspring, leading to the evolution of high egg production in many fish species.
In contrast, mammals have:
* Internal fertilization: This is more efficient than external fertilization, resulting in a higher success rate for fertilization.
* Parental care: Mammals provide extensive care for their young, increasing their chances of survival.
* Lower mortality rates: The combination of internal fertilization, parental care, and internal development leads to lower mortality rates among young mammals.
Therefore, the difference in egg production between fish and mammals reflects the different strategies each group has evolved to ensure their survival and reproductive success in their respective environments.