Dietary emamectin benzoate induces dose-dependent variations in haemato-biochemical and erythrocyte-metric parameters of Oreochromis niloticus (L.)

Abstract

Intensive fish farming often leads to the emergence of infectious and parasitic diseases, which require aquadrugs to control them. The present study evaluated the effects of 1× (50 μg/kg biomass/day) and 3× (150 μg/kg biomass/day) dietary emamectin benzoate (EB)-dosing on healthy Oreochromis niloticus for 7 consecutive days in comparison with control. Dietary EB caused a significant dose-dependent reduction in feed intake and an increase in mortalities. The total erythrocyte counts (TECs), monocyte counts (MCs), haemoglobin (Hb), haematocrit (Ht), and mean cell haemoglobin concentration (MCHC) reduced significantly. Contrarily, the counts of total leukocytes (TLCs), thrombocytes (TCs), lymphocytes (LCs) and neutrophils (NCs) increased significantly within 7 days of EB-dosing (ED) in both groups. The TECs, Hb, TCs and MCs normalized on day 35 post-EB-dosing (PED), while Ht, MCH, LCs, and MCs recuperated on day 14 PED. Both groups experienced a significant increase in serum glucose, alkaline phosphatase, alanine transaminase, aspartate transaminase and creatinine levels as well as a decrease in calcium, chloride ions and acetylcholinesterase levels during the ED period. The alkaline phosphatase and creatinine levels of the 1× group recovered on day 14 and 28 PED, respectively but not in the 3× group. The dosed fish documented reduced erythrocyte cellular and nuclear morphometry like larger axis, minor axis, volume, and surface area, which recovered during the PED period, except for the nuclear volume. The results suggested the tolerability of O. niloticus juveniles and their ability to mount adaptive responses to the effect of EB to recuperate with the suspension of dosing.