Abstract
Intermuscular bones (IBs) are widely present in morphologically generalized teleost fishes and are commonly found in the Cyprinidae. Intermuscular bones are small, hard spicules of bone that are formed by ossification in the myosepta between neighboring myomeres. Why fish have IBs, and whether there is any evolutionary pattern to their occurrence, has been poorly understood. However, the presence of IBs does substantially affect the meat quality and commercial values of many cyprinid fishes in aquaculture. In this study, we sampled 592 individuals of cyprinid fishes to systematically investigate the evolution of IBs from a phylogenetic point of view. We found that the total number of IBs in the Cyprinidae ranged from 73 to 169, and we clarified that only two categories of IBs (epineural and epipleural) were present in all examined cyprinids. Most of the IBs were distributed in the posterior region of the fish, which might be an optimal target for selecting fewer IB strains in aquaculture. There was a positive correlation between IBs and the number of vertebrae, thus making it possible to predict the approximate number of IBs by counting the number of vertebrae. Although the IBs displayed some correlation with phylogenetic relationships in some lineages and to ecological factors such as diet (especially carnivore), in an overall view the variations of IBs in cyprinids were extremely diverse. The number and patterns of IBs in these fishes may reflect their phylogenetic history, but have been shaped by multiple environment factors. In this study, we also confirmed that X‐ray photography remains an optimal and reliable method for the study of IBs.
Highlights
Cypriniformes constitute the largest monophyletic group of freshwater fishes on the earth, with 4,000+ species recognized and some 2,000+ species still awaiting description (Mayden et al, 2009; Stout, Tan, Lemmon, Lemmon, & Armbruster, 2016).Containing the vast majority of taxa found in the Cypriniformes, the Cyprinidae is the most speciose family of freshwater teleosts, including more than 3,000 species (Nelson, Grande, & Wilson, 2016)
The maxi‐ mum and minimum numbers of Intermuscular bones (IBs) were found in the Gobioninae and the Barbinae
The maximum and min‐ imum numbers of epineurals were present in the Leuciscinae and the Barbinae, while the maximum and minimum epipleural numbers were found in the Gobioninae and the Cyprininae, respectively (Figure 3a)
Summary
Cypriniformes constitute the largest monophyletic group of freshwater fishes on the earth, with 4,000+ species recognized and some 2,000+ species still awaiting description (Mayden et al, 2009; Stout, Tan, Lemmon, Lemmon, & Armbruster, 2016). Almost all species of cyprinids have IBs. According to the position of attachment in fish muscle, IBs have been subdivided into three categories, namely epineural, epicentral, and epipleural (Owen, 1866). Techniques for studying IBs are mainly from anatomy (dissec‐ tion), clearing and staining, and radiography All these methods have both advantages and disadvantages and are applicable for different purposes. An interesting pattern concerning the ossification pro‐ cess of IBs has been reported: The ossification of IBs of most fishes progresses from the posterior to the anterior regions of the body (e.g., Danio rerio, Yao et al, 2015, H. molitri, Ke, Zhang, Jiang, & Bao, 2009 and M. amblycephala, Wan et al, 2014); in Anguilla japonica the opposite situation is found (Yao et al, 2015). The main purposes of this study were as follows: (a) to evaluate the reliability of radiographs in counting the number and shape of IBs; (b) to study the number of IBs from a phylogenetic perspective; and (c) to find whether there are any relationships be‐ tween IBs and potential ecological factors
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