Interspecific hybridisation of seahorses and pipefishes

Project Seahorse cautions against mating across different species (hybridization) of seahorses and pipefishes (syngnathids). Trade in hybrid offspring of such matings may compromise captive breeding programmes and release of hybrids poses high risks to wild populations. In order to reduce the potential for hybridization we recommend that anyone currently holding or intending to hold syngnathids:

  • maintains single-species tanks wherever possible;
  • considers giving the name of any doubtful syngnathids to the genus level only e.g. naming seahorses simply as Hippocampus spp;
  • avoids distributing any syngnathids that remain unidentified at the species level without full disclosure of their status;
  • refrains from acquiring syngnathids for any collective breeding programme without reliable information on their origins and taxonomy (this may require genetic or morphological investigation);
  • uses syngnathids with questionable origins or taxonomy only for display or educational work and control their populations carefully.

Aquarists will need to be careful about avoiding hybrids, especially as such general confusion about sources and identities (taxonomy) of syngnathids still prevails.  As with all other species, syngnathids specie are generally reproductively isolated from each other in the wild. Biological or physical barriers usually preclude hybridization in the wild, even where species’ ranges overlap. The aquarium environment can actually promote hybridization by removing these barriers, and by holding geographically separate species together at high densities.

Aquarists should also note that hybrids – which may appear desirable because of their unusual features – might display reduced survivability and reproductive potential when compared to the parent species.

Project Seahorse is concerned that syngnathid hybridization in the aquarium community will hamper the development of collective programmes of captive breeding (see Project Seahorse Aquarium position statement). A key goal of such work is to ensure that the most genetically diverse and healthy populations of syngnathids, of known origin and founder number are retained.  Achieving this goal means that all information about the animals involved must be very accurate, and fully shared.

It is important to realise that release of hybrids, accidentally or by intention, may severely damage wild syngnathid populations (see Project Seahorse Releases position statement). Public zoos and aquaria have guidelines on disposal of animals but these do not control the fate of animals in the private domain. Hybrids that survive release may successfully mate with wild syngnathids and potentially introduce new and harmful genetic material to the native population, thereby reducing survival, growth and reproductive output. Different populations and species of syngnathids that have evolved in different geographic regions and under different conditions display local adaptations, regulated in part by their genetic material.

Successive breeding with released hybrid syngnathids could gradually destroy local population adaptations that have taken millions of years to evolve, reducing the population’s chances of survival.