The Marine Betta or Comet (Calliplesiops altivelis) is commonly mistaken for a bass or grouper which belong to the family Serranidae, however, in reality the Comet belongs to the family Plesiopsidae, commonly referred to as the Roundheads.
As is almost always the case, the bigger the tank the better. However, as a general rule a Comet should not be kept in any tank under 230 litres (60 gallons). Ample rockwork is also important as the caves and crevices formed by the rocks will provide the Comet an opportunity to get out of the brightly lit areas of the tank, as well as, hide from any perceived threats. Subdued lighting is preferable as in the presence of bright lights the Comet is likely to remain in the darkest part of the tank for the entire day.
Comets are reef safe and will not harm your corals and anemones. On the other hand, Comets will consume any fish or crustacean small enough to fit in its mouth. For this reason, it is advisable to keep Comets with similar sized fish. The aquarist should also take care not to place this fish with particularly aggressive species such as basses, triggers, puffers and large moray eels. Another thing to note is that many a hobbyist has lost a Comet to starvation due to over competition for food. Thus, take care to ensure that your tank isn’t stocked with too many fish that are likely to take all the food for themselves.
Finally, you should only keep one Comet per tank unless the tank is massive. It is hard to put an exact figure on what size tank would safely accommodate more than one comet, however, it is safe to say that it would probably be more than a couple thousand litres.
Selection with these fish is easy. If the fish is eating, it is healthy. These fish tend to be in good health or almost dead. There is no middle ground.
Comets are carnivorous, mostly consuming small fishes, crustaceans and worms in the wild. They can at times be trained onto non-living meaty foods but you should be able and willing to offer live if necessary. Ghost shrimp (“gut-loaded”) are great here; and small live bearers like guppies and mollies. Note that this is a nocturnal species in the wild but it can be trained to out more during lights-on hours as it becomes accustomed to your system. At any length, initially you should feed it during the late evening. Having a good deal of healthy live rock and a large deep sand bed will help assure that your comet has plenty of endogenously produced live food items.
Comets are one of the hardiest, most pathogenic disease-resistant fishes in the marine hobby. They are often one of the last fish to show signs of infestation or perish from common parasites like Cryptocaryon. Likewise, it is not sensitive to commonly employed medicine treatments, such as copper based medication and hypo-salinity treatments.
Comets spawn in the darkness of a cave; laying a sticky mass of a few hundred eggs that is guarded by the male. Eggs hatch in about 5 or 6 days depending on temperature. This species is likely protogynic synchronous hermaphrodites. Starting as females, becoming males in time. Therefore, procuring two smaller individuals will likely result in one of each sex. Marine bettas have been captive-bred and reared by a few commercial outfits.