Chinese Bahaba (Bahaba taipingensis) (Fig. 1B), also known as the giant yellow croaker, is one of the largest croakers (Sciaenidae family). It has very limited geographical distribution for it can only be found in south China, from the Pearl River Estuary (PRE), Hong Kong, Macau, and northwards to the Yangtze Estuary. What’s worse lies in the fact that human activities (e.g., overfishing, coastal pollution, etc.) have further threatened their habitats, causing a dramatical decline in its population (Wei and others 2021; Zhang and others 2018). As a “Giant Panda” fish species, Chinese Bahaba has been listed among the national first-class wildlife protection animals and China's top 10 genetic resources of aquatic products in China since 2021. Moreover, as a critically endangered (CR) species that is of highly commercial value in that its swim bladder is commonly used in traditional Chinese medicine, it is confronted with an extremely high risk of extinction in the wild (IUCN 2020; MARAC 2021a; MARAC 2021b).
As a member of the Sciaenidae family, Chinese Bahaba has also been found to generate some species-specific sounds for communicative purposes during reproduction, and feeding, etc. It is more sensitive to sounds compared to other fish families (Wei and others 2021; Zhang and others 2018). However, few reports have been found regarding the sound capture, particularly, the foundation of material structure of the members of the Sciaenidae family including Chinese Bahaba.
Fish otoliths are the sensory organs immersed in the endolymph helpful for maintaining balance and hearing (Armarego Marriott 2021; Popper and Lu 2000; Söllner and others 2003). They were found of metabolically inert carbonate structure, that is, they have been subject to no chemical alterations or reabsorption whenever formed (Söllner and others 2003). Chemically, they are mainly composed of calcium carbonate and precipitated as aragonite under a high molecular weight protein matrix (Carvalho and others 2019). This process is regulated by hormones and influenced by environmental factors (Oxman and others 2007). Numerous studies have been reported on the microchemistry of fish otoliths, and the relationships between fish species and their environments, as well as the reconstruction of environments (e.g. (Andrus and others 2002; Brennan and others 2015; Chang and Geffen 2013; Wood and others 2022; Yang and others 2011)). However, rare information has been found about the material structure that affects the fish hearing. This paper takes the initiative in reporting the sound absorption structure and the chambers of otoliths of Chinese Bahaba, the “Giant Panda” fish species. It is expected to provide some enlightenments in protecting and conserving such endangered species.