Reproductive biology

Although anabantoids are a fairly small percomorph group, their members exhibit a great variety of reproductive modes. The primitive mode, which occurs in Anabas, Ctenopoma, and Helostoma, is the absence of parental care with the release of several thousand small (ca. 0.04 in/1 mm), buoyant eggs that float due to a single large oil globule in the egg. After hatching, larvae retain the oil globule, which during development divides into two oil vesicles to the left and right of the chorda and is used as a floating organ. All species of the genus Mi-croctenopoma and most osphronemids build bubble nests and guard primitively buoyant eggs and larvae. Bubble nests can consist of only a few bubbles, as in the tiny cave-brooding species of Parosphromenus, or be large. Mouth brooding has evolved at least twice among anabantoids, once in the lineage Ctenops, Sphaerichthys, and Luciocephalus, and again within the genus Betta.

Unusually for anabantoids, the two species of the purely South African genus Sandelia spawn on a substratum and have adhesive eggs. In groups with parental care, the number of eggs is usually smaller than in those without care, although several thousand eggs may be spawned in some species of Mi-croctenopoma and Trichogaster. The number of eggs may range from 40 to several hundreds in most bubble nest builders, and from 20 to 200 in the mouth brooders. Egg size ranges from 0.03 in (0.7 mm) in Microctenopoma to 0.19 in (3 mm) in Lu-ciocephalus.

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