In this relaxing episode, we would like to present you with a mesmerising performance by Banggai cardinalfish (Pterapogon kauderni) dancing with the swell of the ocean. These beautiful creatures grow to a size of about 8 centimetres (3 inches), which makes them a great bite-sized snack for many would-be predators.
As a solution to deal with this predicament, most young Pterapogon kauderni, as well as some adults, often associate themselves with sea anemones. The stinging cell of the anemone offers them protection from any predators. Adults prefer to spend their time with Long-spines sea urchins (Diadema setosum), to whose spines they can retreat when danger comes around. This behaviour has also been observed with other living benthic substrates like hydrozoans, branching coral and mangrove prop roots.
Watch the Banggai Cardinalfish (Pterapogon kauderni) dance
This beautiful creature can be easily identified from all other cardinalfishes by its tasselled first dorsal fin, elongated anal and second dorsal fin rays, deeply forked caudal fin, and a colour pattern consisting of three black bars across the head and body and prominent black anterior edges on the anal and second dorsal fin, which are decorated with white spots.
Geographical range and name Banggai Cardinalfish
Their common name “Banggai cardinal fish” is derived from the fact that this species has an extremely limited geographical range (5,500 km2) and is restricted to the Banggai Archipelago in Indonesia. It has a very small total population size of an estimated 2.4 million. Since their introduction to the aquarium fish trade in the 90s, a small population also started to occur off Central Sulawesi, within Luwuk harbour. An additional population has established itself in the Lembeh Strait (North Sulawesi), 400 km north of the natural area of the species distribution. Small populations have even been seen in Secret Bay, northwest Bali.
Diet of Banggai Cardinalfish
Pterapogon kauderni is an opportunistic feeder, whose diet consists of planktonic, demersal, and benthic organisms. Although the vast majority of its food intake comes in the form of copepods. Reproduction of this species is a curious affair. After the female chooses a male and seduces him with a dance to win him over, the pair separates themselves from the rest of the group, and establish their own territory, which they will vigorously defend against others. The act of reproduction is done through spawning, whereby the female releases about 40 eggs, all connected by filaments and referred to as a clutch, from her body and into the water, where they are fertilized by the male.
Reproduction of Pterapogon kauderni
But unlike demersal spawners that scatter their eggs in the ocean’s currents, Banggai cardinals are parental mouth-breeders. Within seconds after fertilisation, the male sucks up the eggs and keeps them in his special mouth pouch, where they remain for about 20 days until they hatch. During the incubation period, the male Banggai cardinalfish doesn’t eat. Some scientists think the male may swallow some of the eggs, by accident or design, in order to still get some nourishment.
During this time the female can be observed aggressively defending the male and her offspring. When the younglings hatch, they look like tiny replicas of their parents. For about another week or two after their birth, these juveniles can find refuge from danger in their daddy’s mouth pouch. So, unlike many other species of marine fish that use spawning as a method of reproduction, the Banggai cardinalfish lacks a pelagic phase in its life history.
So much more to uncover
What a beautiful world we live in! This video was filmed at one of the dive sites of Lembeh (Indonesia) in 2019.