Southern Knight Seahorses

Southern Knight Seahorses are temperate marine fish found in coastal waters of south-eastern Australia and also in New Zealand. Seahorses belong to the family Sygnathidae which has over 200 species (half of which occur in Australian waters.) This species is also known as the Large-belly or Big-belly Seahorse.

Seahorses are unique animals which make spectacular aquarium subjects. They have a graceful manner, attractive colouration and are reported to live for up to 9 years in captivity. They also have an unusual prehensile tail which is used to hold onto seaweed or the substrate. Another unusual feature is that when Seahorses breed, the male becomes pregnant and gives birth to hundreds of tiny live seahorses!

Their strange appearance has long fascinated mankind and many people still consider them almost as a mystical creature!
Southern Knight Seahorses are now being commercially produced in Australia, helping to ensure that wild stocks are not over-exploited. Being tank reared, these fish are surprisingly easy to keep. They are quite tolerant of varying water salinity and temperature, will eat frozen foods and come from a disease free hatchery. Being a temperate species, they can also be kept in an unheated indoor aquarium in most regions of Australia.

Tank Set-up

Can be kept in filtered aquaria, or in bowls (20 litres or more is best).
Four to eight 7 cm Seahorses can be housed in a 20 litre bowl with under gravel filtration. (A much larger aquarium is preferable in areas which receive a lot of summer heat).
Twenty-five percent water changes should be done each fortnight, (increase to fifty percent for bowls or aquaria holding less that 50 litres). Seahorses require very well oxygenated water, so air uplifts are essential – standard air-driven under gravel filters and air stones are ideal. Substrate should be shell grit or crushed coral, or a 50/50 mixture of aquarium gravel and shell grit. Tank decorations should be added for the Seahorses to hang on to – well seasoned driftwood or plastic plants which are not too spiky are ideal. Rocks can also be utilized. Do not place live corals in with the Seahorses as the corals may sting and kill them within several days. Seahorses are best kept without any other fish species, as their gentle nature does not allow them to compete for food.

Maximum Size

Grows to 20-25 cm in Australian waters, grows to 30cm in New Zealand in cooler conditions.


Colours can vary as Seahorses are able to mimic their surroundings. Usually olive, white or golden, with variable dark spotting.

Temperature Range

Southern Knight Seahorses soon adjust to temperatures within 12-26°C. with optimum temperatures being 15-22°C. Aquarium heaters are not required in most indoor situations. During heat wave conditions ensure air stones are operating strongly to ensure optimum oxygen levels, and use air conditioning or party ice to hold the temperature below 28C.

Water Conditions

Requires either seawater or artificial seawater, salinity range: 14ppt to 28ppt (1.010 to 1.020 specific gravity). When preparing artificial seawater, ensure the water used contains no chlorine. pH: preferably 8.2 – 8.4, do not exceed 9.0.
Do not use aquarium water that has previously held other fish or invertebrates. Although Seahorses are quite tolerant to ammonia and nitrite, their biological filter will still need to fully establish before the tank is fully stocked.


Southern Knight Seahorses have been trained to eat frozen brine shrimp. At temperatures below 20°C, each Seahorse can eat up to 20-25 brine shrimp once a day. At temperatures between 20°C and 25°C, they should be fed twice a day. They will also eat small frozen krill, and live brine shrimp. In time, Seahorses can learn (reluctantly) to eat flake food, if they are fed a mixture of frozen shrimp and ground flake food. Ensure no uneaten food remains in the aquarium.


Southern Knight Seahorses begin breeding at 4 months of age. Males can be recognized by their belly pouch, they actually inflate the pouch to its maximum extent to try and impress potential mates. During spawning, females transfer their eggs to the male’s pouch where they are nurtured for about 30-50 days, depending on the temperature. Large speciments release broods of 300 – 400 fry. In the wild, males release 3 or 4 broods over summer. The male’s pouch is white and darkens in colour as the eggs develop. newborn fry are about 21mm long and can be fed on live baby brine shrimps.


The key to the wellbeing of seahorses is good water quality and good food, (particularly when kept in small aquariums or bowls).

Unpacking Procedures

Before unpacking, please check temperature of both shipping water and future holding tank.

Please note:
*If the tank is warmer than the shipping water, lower the temperature by adding ice. (Party ice is ideal as it is chlorine free.) The effect of the ice on salinity will be negligible. When the temperatures have equalized, release the Seahorses. The aquarium water temperature will then gradually return to its previous temperature.
*If the holding tank is colder than the transport bag, float the unopened bag for 5-10 minutes or until the temperatures equalize, before releasing the Seahorses.


Southern Knight Seahorses make a fascinating and enjoyable pet. They are also quite easy to keep – if given a few simple requirements such as the correct temperature and filtered water, regular water changes and correct feeding.