Morphological Revision of Thirteen Wild Fighting Fish Species Found in Thailand with an Identification Key

Morphological descriptions of 13 wild fighting fish species were revised by examining specimens collected as near as possible to the type specimen localities. The description has been revised for certainty and consistency. Principal Component Analysis (PCA) and Kruskal–Wallis with Dunn’s post hoc tests were analyzed and revealed previously described morphological characteristics were evaluated for distinguishing features. The PCA showed that the high loading factor of the principal component 1 (PC1) indicated that head length (0.221) was beneficial for the fish species identification. The Kruskal–Wallis test indicated the significant differences in morphometric characteristics among the fish species (p < 0.05). Then the significant differences in Dunn’s post hoc test (p < 0.001) in head length distinguished the mouth-brooders (i.e., Betta apollon, B. ferox, B. kuehnei, B. pallida, B. pi, B. prima, B. pugnax, and B. simplex) from bubble-nesters (i.e., B. imbellis, B. mahachaiensis, B. siamorientalis, B. smaragdina, and B. splendens) with a head length range of 29.27–36.42 vs. 24.14–28.31% of standard length, including the symmetrical caudal fin. Some characteristics distinguish the fish into subgroups and some species, such as a greater number of anal soft fin rays and lateral line scales of B. pi among the mouth-brooding species (28–29 vs. 22–26 fin rays and 33–35 vs. 26–32 scales) or of B. smaragdina among the bubble-nesting species (26–28 vs. 22–25 fin rays and 31–33 vs. 27–30 scales). Additionally, descriptive characteristics such as anal and caudal fin shape and melanophore pigmentation on the head, body, and fins, including the coloration of live specimens, are useful for distinguish among species and generating a dichotomous identification key.