Early-life histories, morphological development, and dichotomous keys of seven wild mouth-brooding fighting fish species (Actinopterygii, Osphronemidae)
Within the family Osphronemidae, mouth-brooding fighting fishes are small, air-breathing fish species that hold their eggs and offspring in their buccal cavities as a parental care behavior, usually found in running waters and distributed in the wild throughout Southeast Asia. This study aims to describe the morphological development and generate identification keys for the larval and juvenile stages of seven wild mouth-brooding fighting fish species found in Thailand, i.e., Betta apollon, B. ferox, B. pallida, B. pi, B. prima, B. pugnax, and B. simplex from the wild. The broodstocks were collected from type localities or based on characteristics that most closely matched each species description, with healthy fishes selected and breeding continued for our size-series collection, including B. simplex, a previous study. The results showed that mouth-brooders released their offspring when developed to the post-flexion stage within 11–12 (mode = 11) days after fertilization (DAF), except B. pi, which took 18–20 DAF, and the post-flexion larva developed to the juvenile stage within 18–30 days after release. The main characteristics of the new-release post-flexion larva were an oblong and depressed body, a large head, an oval to rounded eye, and rays where the caudal fin began to develop, as well as having fully developed ventral fins with two or three dorsal, central, and ventral stripes and a caudal spot. Myomere numbers and fin rays differed among species across a range of 8–10 dorsal, 10–13 pectoral, 6 ventral, 24–31 anal, and 10–13 caudal fin rays. Diagnostic characters were selected to create a dichotomous identification key, with an illustration provided. In terms of taxonomy, the different larval stages also differed in pigmentation patterns among species, with pigmentation patterns on head (pre-orbital, sub-orbital, post-orbital, and sub-opercular bands) and longitudinal stripes on the side of the body able to be used to distinguish among different development stages as well as different species.
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