In seahorses it is the males that become pregnant and give birth, using a specialized brood pouch where females deposit eggs and males fertilize, incubate and eventually release fully formed young into the water.
Overview
Seahorses belong to the family Syngnathidae, which also includes pipefish and seadragons. A remarkable feature of many species in this family is male pregnancy: after courtship the female transfers eggs into the male’s brood pouch. The male then fertilizes the eggs internally and provides a protective, regulated environment where embryos develop until birth.
Brood pouch and pregnancy
The brood pouch is a complex structure with tissue that supplies oxygen and nutrients, removes waste and helps regulate salinity for the developing embryos. Depending on species, a male can carry from a few dozen to over a thousand eggs. Incubation periods vary with temperature and species, after which the male undergoes muscular contractions to expel the young in a process that resembles giving birth.
Evolutionary context and benefits
Male pregnancy is rare but not unique to seahorses; close relatives show related adaptations. Shifting parental investment to males may increase reproductive efficiency: females can produce another clutch sooner while males enhance offspring survival by protecting and provisioning embryos. This role reversal has ecological and behavioural consequences for mate choice and mating systems.
Conservation note
Many seahorse species face threats from habitat loss, bycatch and the aquarium and traditional medicine trades. Conservation efforts include habitat protection and fisheries management to preserve these unusual and ecologically important fish.