Effects of Acute Hypoxia Stress on the Tissue Structure of Spleen and Heart of Juvenile Eleutheronema tetradactylum

Abstract

【Objective】The study was carried out to explore the effects of acute hypoxia on the survival of juvenile Eleutheronema tetradactylum and their spleen and heart tissue structure, with a view to providing technical support and theoretical references for the breeding and production of this species.【Method】Filling water with nitrogen to quickly overflow oxygen and reduce the content of dissolved oxygen in the water. Different levels of dissolved oxygen treatment were set in the experiment: normal oxygen group (6.33 ± 0.15 mg/L), moderate hypoxia group (3.99 ± 0.18 mg/L), and severe hypoxia group (2.05 ± 0.15 mg/L). Each treatment group was set up with 3 parallel devices. During the experiment, the flowing water was turned off, and the dissolved oxygen level in the water was monitored in real time by using a dissolved oxygen measuring instrument. The corresponding dissolved oxygen level was maintained by adjusting the size of the inflation valve. Using paraffin embedding, sectioning and hematoxylin eosin (HE) staining methods were used to observe the changes in tissue structure of the heart and spleen of juvenile E. tetradactylum.【Result】In terms of mortality rate, there was no mortality observed in the E. tetradactylum in the normal oxygen group; the mortality rates of juvenile fish under the stress in the moderate and severe hypoxia groups were 10.0%-13.3% at 23 hours, 30.0%-40.0% at 26 hours, and 43.3%-53.3% at 29 hours. In terms of spleen tissue structure, compared with the normal oxygen group, the moderate hypoxia group showed an increase in white pulp and the number of lymphocyte in juvenile fish, sparse distribution of peripheral red pulp, and a decrease in the number of melanin macrophages; the red pulp area of juvenile fish in the severe hypoxia group expanded, with a decrease in the white pulp area and the number of lymphocytes, and melanin macrophages rarely appearing. In terms of heart tissue structure, the compact layer of heart tissue in juvenile fish in the moderate hypoxia group became thinner, the myocardial fibers in the sponge layer became thinner, and the spacing became wider, and partial myocardial fiber rupture phenomenon occurred; the degree of thinning of the compact layer and thinning of the myocardial fibers in the sponge layer of juvenile fish in the severely hypoxic group increased, and the degree of expansion of the interstitial space increased compared to the hypoxic group, with partial myocardial cell rupture, nucleus protrusion, myocardial fiber rupture, and disordered arrangement.【Conclusion】The study has shown that acute hypoxia stress can affect the survival rate of juvenile E. tetradactylum. The lower the dissolved oxygen level, the higher the mortality rate, and the degree of tissue structure damage increases with the level of hypoxia.

Keywords

• eleutheronema tetradactylum
• acute hypoxia stress
• spleen
• heart
• tissue structure