Explanation:
Reproduction in Fishes. Nearly all fish reproduce by sexual reproduction - the fusion of sperm produced from testes and eggs produced from ovaries. ... Fertilization is external in most fish species. Large quantities of eggs and sperm are simultaneously released into the water by females and males.
Because we know that 15% of the population does not have the allele we can assume that at least 85% of the population has at least on copy of the dominant allele.