The features of the morphology of the heart of Clarias gariepinus (Siluriformes, Clariidae)

One of the promising fish species that has relatively recently started to be farmed in Ukraine is the African catfish (Clarias gariepinus Burchell, 1822) from the catfish family. It is a freshwater, warm-water, omnivorous fish that can breathe atmospheric air. The purpose of this study is the morphological evaluation of the macroscopic structure of the heart of the African catfish, a member of the class Actinopterygii, family Clariidae. It is shown that the heart of the African catfish is topographically located in the cranial part of the body, on the ventral side, near the head in the triangle between the shoulder girdle bones, occupying a central position between the gills. The heart of the African catfish consists of the venous sinus, atrium, ventricle, and arterial cone, which are separated by valves, allowing blood to move only in one direction - from the venous sinus to the arterial cone and not vice versa. As a distinct structure, the atrium is located to the right of the ventricle, with an incomplete septum partially dividing the atrium into right and left halves (chambers). The ventricle of the heart is a hollow organ with an elongated oval shape. The cranial part of the ventricle has an expanded base, while the caudal part has a convex apex. The arterial cone of the heart has an expanded base, which adjoins the ventricle, and its opposite part is narrowed, giving the structure a conical (funnel-like) shape. According to organometry results, the linear dimensions of the heart components vary and depend on their functional load during the rhythmic contractions of the heart muscle in the cardiac rhythm, during which blood flows through the vessels to all organs. The ventricle's largest linear parameters - length, width, and thickness - are characteristic. In contrast, the linear parameters of the arterial cone and atrium are significantly smaller. Based on the ventricular development index, the heart of the African catfish is classified as narrow-elongated. It has been established that the thickness of the ventricle wall is the greatest among all its anatomical structures, measuring 3.2 f 0.4 mm. The wall of the arterial cone is statistically 1.47 times thinner than that of the ventricle wall and the atrial wall thickness is the smallest (8.0 times smaller) compared to the ventricle wall. The absolute and relative masses of the ventricle, arterial cone, and atrium correlate with their linear parameters: the greatest absolute mass is found in the ventricle - 0.52 f 0.02 g, followed by the arterial cone - 0.21 f 0.03 g, and the atrium - 0.16 f 0.03 g. According to these morphometric results, the coefficient of the ratio of the ventricle's absolute mass to the total heart mass is 1:0.58, the ratio of the arterial cone's absolute mass to the total heart mass is 1:0.24, and the ratio of the atrium's absolute mass to the total mass of the ventricles is 1:0.18. The study of the structural characteristics of the cardiovascular organs serves as a foundation for ichthyologists and fish farmers to conduct disease prevention measures and to mitigate the impact of stress and adverse environmental factors on the fish during aquaculture.