Abstract

This study was designed to evaluate the tolerance of Clarias gariepinus juveniles to a gradual and abrupt increase in salinity over time. To this effect, C. gariepinus juveniles were exposed to three salinity incremental protocols namely 1 g L⁻¹ day⁻¹, 5 g L⁻¹ day⁻¹, and 10 g L⁻¹ day⁻¹. Changes in the hematological parameters and the gill histology of fish were analyzed to determine the impact of osmotic stress on the health status of the fish and its osmoregulatory ability. The result obtained showed that juveniles of C. gariepinus can tolerate salinity stress up to 14 g L⁻¹. At 15 g L⁻¹ and beyond, all samples died regardless of gradual (i.e., 1 g L⁻¹ day⁻¹ administered for 15 days) or abrupt salinity exposure (i.e., 5 g L⁻¹ day⁻¹ administered for three days and 10 g L⁻¹ day⁻¹ administered for two days). Interestingly, more than 90% of the fish survived a direct 10 g L⁻¹ exposure for 24 h without prior acclimation. The hematological parameters accessed in the fish exposed to 10 g L⁻¹ (either gradually or abruptly) showed a significant increase in the white blood cells and a decrease in the red blood cells, packed cell volume, hemoglobin concentration, and all derived blood parameters. The results of the serum biochemistry show a lower total protein and albumin in the salinity-treated fish compared to the control group. However, the serum glucose and the plasma electrolytes (i.e., K⁺, Na⁺, and Cl⁻) were higher in the former group than in the latter. Aside from the stress response expressed in the blood parameters, severe gill degenerations were seen in the histological micrograph obtained for the salinity-treated fish, while the control had a near-normal gill architecture. It was concluded that C. gariepinus could tolerate salinity exposure of 10 g L⁻¹ day⁻¹ (administered gradually or abruptly) and below without killing the fish within 24 h.

中文翻译：

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Clarias gariepinus 的耐盐性（Burchell，1822）：了解血液参数变化和鳃组织学变化

摘要

本研究旨在评估Clarias gariepinus幼鱼对盐度随时间逐渐和突然增加的耐受性。为此，将C. gariepinus幼鱼暴露于三种盐度增量方案，即1 g L ^-1  day ^-1、5 g L ^-1  day ^-1和10 g L ^-1  day ^-1。通过分析鱼的血液学参数和鳃组织学的变化，以确定渗透胁迫对鱼的健康状况及其渗透调节能力的影响。结果表明，C. gariepinus幼鱼能够耐受高达14 g L ^-1的盐度胁迫。在 15 g L ^-1及以上，无论是逐渐（即 1 g L ^-1 天^-1施用 15 天）还是突然的盐度暴露（即 5 g L ^-1 天^-1施用 3 天），所有样品都会死亡10 g L ^-1 天^-1施用两天）。有趣的是，超过 90% 的鱼在没有事先驯化的情况下直接暴露于 10 g L ^-1 24 小时后存活下来。暴露于 10 g L ^-1（逐渐或突然）的鱼的血液学参数显示，白细胞显着增加，红细胞、细胞压积、血红蛋白浓度和所有衍生血液参数显着减少。血清生化结果显示，与对照组相比，经盐处理的鱼的总蛋白和白蛋白较低。然而，前者的血糖和血浆电解质（即K ⁺、Na ⁺和Cl ^-）高于后者。除了血液参数中表达的应激反应外，在经盐度处理的鱼获得的组织学显微照片中还发现严重的鳃退化，而对照鱼则具有接近正常的鳃结构。结论是，C. gariepinus可以耐受 10 g L ^-1  day ^-1 （逐渐或突然施用）及以下的盐度暴露，并且在 24 小时内不会杀死鱼。