Changes in the amount of kidney pigmented macrophage aggregates throughout the breeding cycle of female Ohrid trout, Salmo letnica Kar. (Teleostei, Salmonidae)

Abstract

Changes in fish macrophages (Macs) are useful indicators of environmental pressures, but responses due to chemical and nonchemical stresses may be confounded by natural sources of variability. These may include sex and gonadal stage. In this study, we start addressing the following question: is the seasonally dependent ovary stage a factor to consider when using kidney Macs as biomarkers? To tackle this problem, the relative amount of pigmented Macs in kidney (head, trunk, and tail portions) was stereologically estimated in Ohrid trout, and related with the breeding status. The amount of Macs significantly increased from pre vitellogenesis to late vitellogenesis and showed a decreasing trend then after, with lower values noted after spawning in the head (1.9% versus 7.5% versus 2.0%), trunk (1.8% versus 7.5% versus 2.5%), and tail (2.5% versus 6.7% versus 2.9%) kidney. The decrease seen at spawning was significant in head and trunk kidney, and at post spawning it was significant for all kidney portions. The amounts of Macs were positively correlated with the ovary relative weights and plasma estradiol levels. We proved for the first time that fish kidney pigmented Macs can vary in amount during the breeding cycle. Our data, combined with literature, strongly support that the sex-steroid profile and kidney status-seasonal remodeling both influence the Macs pool; likely not only in female trout. So, while increases in Macs may warn of ecosystem problems, we show that using kidney Macs for biomonitoring should also take into account seasonally, particularly that related with ovary maturation.