![]() ![]() The entire fertilisation process in seahorses is therefore uniquely efficient among vertebrates, yet paradoxically involves several steps that would seem to complicate, and even appear to prevent, the interaction of the gametes. In addition to this, the yellow seahorse produces extraordinarily low quantities of dimorphic spermatozoa, but is nevertheless highly fertile and can produce broods that exceed 100 embryos. Observations of courtship and mating behaviour also revealed that the pouch closes immediately after mating, and that sperm transfer must occur within a time window of no more than 6 s. Anatomical dissections showed, however, not only that direct sperm deposition into the pouch is physically impossible, but that spermatozoa must somehow travel a significant distance (>4 mm) outside the body of the male, to reach and fertilise eggs in the pouch. This has contributed to a widespread, but poorly founded belief, that the eggs are fertilised using spermatozoa that are deposited directly into the brood pouch via an internal sperm duct. Uniquely among vertebrates, seahorses and pipefishes (Family Syngnathidae)incubate their eggs within a male brood pouch.
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