If a sperm cell contains 8 chromosomes, it comes from an animal that has 16 chromosomes.
This is because the animal's sperm cells and egg cells (also known as gametes) contain half the number of chromosomes as the animal's somatic cells (also known as diploid cells). During fertilization, the sperm cell and egg cell combine to form a zygote, which contains the full complement of chromosomes for the animal. For example, a human sperm cell contains 23 chromosomes, and a human egg cell contains 23 chromosomes, for a total of 46 chromosomes in the fertilized egg.