Reproduction in Sea Horses

     In sea horses, the males become pregnant.  Their mating involves the female inserting her oviduct into the male's brooding pouch.  She does this several times for short intervals to avoid exhaustion.  In between the female rests while the male contorts himself to try to get the eggs in place in his brood pouch.  After completion the male moves away and attaches himself by his tail to a nearby plant.  The female moves away and waits for her oviduct to recede.  The oviduct usually recedes within a few hours.  The eggs are fertilized and hatch in the male's pouch (Graham 1939).  The size of the sea horse brood varies within sea horse species.  Some species' broods are as large as 200 (Graham 1939) while others are as small as 8 (Breder 1940).

This is a pregnant male sea horse.  The brood pouch is the distended part of the abdomen. 
Photo courtesy of A. Vincent (1992).
     The males are pregnant for several weeks before giving birth to their brood (Vincent, et. al 1992).  When they prepare to give birth, the pouch extends to an almost spherical shape.  The male also undergoes muscular contortions - a forward and a backward bend - that last for about ten minutes.  then in an explosive action the brood leaves the pouch.  After the last young sea horse has left, the pouch returns to its normal position, which usually takes about an hour (Breder 1940).  Males are ready to re-mate within a few hours of giving birth (Vincent, et. al 1992).

Two sea horses mating.
Photo courtesy of Rudie Kuiter and NOVA Online.
Sex Role Reversal
     Since the males sea horses are pregnant, much speculation has been made as to whether or not they are sex role reversed.  Sex role reversal involves the female competing for males as a mate.  Male parental care is not a determinant in sex role reversal.  Research by Vincent and others (1992) has shown that sea horses are not sex role reversed, though several species of pipe fish are.  Also, the sea horses demonstrate a monogamous relationship.  Males provide parental care for the young.  While the young are in the pouch, males give oxygen through a capillary network, transfer nutrients, and change the atmosphere in the pouch.  The atmosphere change in the pouch makes the inside of the pouch contain more salt water so the young will be prepared to go into the ocean water when they are born (Vincent, et. al 1997).

If you have any questions, please contact Leslie Cook.