Morphological description of Chaetostoma thomsoni Regan, 1904 (Siluriformes, Loricariidae), an endemic fish species from Colombia

The Porce River basin, where the Porce II and Porce III reservoirs are located, is home to a wide variety of endemic ichthyofauna species, most of which still do not have descriptions of their anatomy and histology. Chaetostoma thomsoni, known as “Striped rubbernose plecostomus” and Cucha or Carachama in South America. It is a teleost fish of the order Siluriformes, family Loricariidae, which is usually abundant in the ecosystems of rivers and streams with fast currents and moderate slopes. This species is abundant in the Magdalena ̶ Cauca River basin in Colombia. This study aimed to describe the anatomical and histological characteristics of the skin and the internal organs of C. thomsoni from the Porce River basin. For this, 37 specimens of C. thomsoni were captured in streams by electrofishing or cast net. The specimens were immersed in Eugenol solution (300 mg/L) as euthanasia, then preserved in 10% buffered formalin solution, labeled, and stored individually in Falcon tubes. Subsequently, the fish were transferred to the Animal Anatomy Laboratory of the University of Antioquia to perform the biometry, dissection, and sample collection. As a result, the complete morphometric study of the species was obtained, in addition to a detailed description of its skin and internal anatomy, where it was possible to identify macro and microscopic structures of organs such as intestines, hepatopancreas, spleen, kidney, urinary bladder, gonads, among others. This detailed anatomical description provides valuable information about the health of the animals and aspects of applied anatomy, such as knowledge of the appropriate puncture site for taking blood samples through cardiopuncture. Another interesting finding was the shape of the cephalic kidney, with a bifurcated arrangement cranially, partially enveloping the brain. In addition, both the cephalic kidney and its caudal portion showed interstitial hematopoietic tissue, endocrine, and immunological functions. The Stannius corpuscles, as in another fish species, in C. thomsoni, are evident in two nodules at the last third of the caudal kidney. Completing this anatomical description is essential for future research that will help to generate new knowledge that promotes the protection of endemic Colombian ichthyofauna.