Introduction:
Animals that exhibit external fertilization produce a large number of gametes. This reproductive strategy is seen in various aquatic animals like fish, amphibians, and some invertebrates. External fertilization involves the release of gametes, both eggs, and sperm, into the external environment, where fertilization occurs. The large number of gametes produced by these animals serves several important purposes.

Advantages of producing a large number of gametes:

1. Increased chance of fertilization: External fertilization requires a high number of gametes to increase the probability of successful fertilization. Since the gametes are released into the external environment, they face numerous challenges such as dilution, predation, and physical barriers. By producing a large number of gametes, the chances of finding a mate with compatible gametes and successfully fertilizing them are significantly improved.

2. Compensation for low survival rates: External fertilization is associated with relatively low survival rates of gametes. Factors like temperature, pH levels, water current, and predators can significantly impact the survival of gametes. By producing a large number of gametes, animals can compensate for the high mortality rates and increase the chances of successful fertilization and offspring production.

3. Genetic diversity: External fertilization allows for the mixing of gametes from different individuals, promoting genetic diversity within a population. By producing a large number of gametes, animals increase the likelihood of encountering a genetically diverse set of potential mates. This genetic diversity is crucial for the adaptation and survival of the species in changing environments.

4. Competition among gametes: With a large number of gametes present in the external environment, there is increased competition among them for successful fertilization. This competition ensures that only the fittest and most compatible gametes have a higher chance of fertilizing an egg. It helps in maintaining the quality of the genetic material passed on to the next generation.

5. Environmental variability: External fertilization allows animals to reproduce in environments with unpredictable or fluctuating conditions. By producing a large number of gametes, they increase the likelihood of successful reproduction even when the environmental conditions are suboptimal. This adaptability is particularly advantageous in habitats where the availability of mates or suitable conditions for reproduction can vary greatly.

Conclusion:
To improve the chances of successful fertilization, genetic diversity, and survival in the face of environmental challenges, animals exhibiting external fertilization produce a large number of gametes. This reproductive strategy ensures the propagation of their species by compensating for the risks and uncertainties associated with external fertilization.