Quantitative and Weight Indicators of African Catfish Eggs and Larvae Development under Exposure to the Low-Power Ultrasound

Introduction. The growth of the world population and changing climate conditions on the planet induce the search for the innovative methods and technologies capable to increase the productivity and efficiency of the agricultural sector, and in particular — industrial fish-farming. In recent years, ultrasound has become one of such methods, widely used in many industries due to its unique properties and capabilities. In fish-farming, the use of ultrasound can significantly improve the processes of fish breeding by increasing the growth rate, improving digestion and overall health of fish, however, the issue of biostimulation of eggs and larvae with low-power ultrasound remains unexplored. The aim of this work is to study the biostimulation of eggs and larvae of African (clarias) catfish with ultrasound in aquariums as an advanced method of improving the growth and survival of this biological object at the early stages of its development, as well as a potential method for preventing the infectious and invasive diseases. Materials and Methods. The object of this study is an African clarias catfish, also known as the marbled clarias catfish (Clarias gariepinus). During the experiment, carried out at the fish-farm the “Marbled Catfish” Fish Farm” LLC (Lipetsk) from March to September 2023, 4 groups were formed — three experimental and one control. The eggs and larvae of the African catfish were exposed to the low-power ultrasound, in the experimental groups the exposure lasted for 30 s, 60 s and 120 s, respectively; the control group didn’t undergo any ultrasonic treatment. Biostimulation was carried out with a low-power submersible source of ultrasonic waves (0.243 W/cm 2 ) and was performed 6 times. Sorting was carried out on the 15-th day from the start of incubation. In total, four series of experiment were carried out. Results. The first, second and third groups in all series of the experiment, according to sorting results, contained the largesized larvae of the African catfish in a percentage ratio of 44 to 46%; the percentage of the large-sized larvae in the control group was 19%. In terms of average-size, sorting gave the following result: in 1–3 experimental groups — from 52 to 54% of the total number of larvae; in the control one — 72%. For small-sized larvae, the following values were obtained: in groups 1–3 — from 2 to 3%, in the control group — 9% of the total number of larvae in the groups and series, respectively. Discussion and Conclusion. The growth and development of African catfish eggs and larvae are greatly influenced by the hydrological parameters of water: temperature, oxygenation, illumination, pH, hardness, content of hydrocarbonates, phosphates, nitrates and other chemical elements. In addition, fertilization of eggs may occur unevenly due to non-uniform mixing of eggs and milt, quality and maturity of eggs during fertilization, which can result in different quantitates of the catfish larvae output. The exposure of eggs and larvae to the ultrasound in the experiment resulted in an increase of a number of large-sized larvae, which is favourable for obtaining the fish seed material. Timely sorting of fish seed material before transferring an African catfish to the closed water supply systems reduces the cannibalism during further cultivation. The use of ultrasound in fish-farming requires further study to identify the optimal frequency of treatment and the effect on the commercial fish immunity and growth rate, which will foster the satisfaction of the growing needs of the population in the high-quality products of fishing industry.