An autofluorescence‐based survey of late follicular atresia in ovaries of a teleost fish (Thunnus thynnus)

Abstract

In this study, the authors examined late atretic follicles in the ovaries of Atlantic bluefin tuna, Thunnus thynnus (Linnaeus 1758), at different times of the year using transmitted light and epifluorescence microscopy. Atresia (degeneration and resorption of developing ovarian follicles) is a natural process involved in fecundity downregulation in teleosts and is substantially enhanced in stressful conditions. Early (α and β) atretic stages of yolked oocytes have a relatively short duration in seasonally reproducing species, whereas later (γ and δ) atretic follicles (LAF) persist for longer time in the ovary, serving as a sign of previous vitellogenic activity. LAF can thus be used as reliable markers of maturity during non-reproductive periods. Lipofuscin granules accumulate in the cytoplasm of LAF cells as a result of lysosomal digestion of oocyte components. Taking advantage of the well-known autofluorescent properties of lipofuscins, LAF may be identified in unstained histological sections under fluorescence microscopy using appropriate excitation and emission wavelengths. The authors explore in this study the applicability of fluorescence microscopy to provide a fast and effective method to assess late atresia in fishes. This method may be particularly useful to determine sexual maturity in individuals sampled long after the spawning season, where LAF are difficult to detect in standard histological sections. Furthermore, LAF autofluorescence provides a rapid way to quantify late atresia in fishes using image analysis.

Atresia of ovarian follicles in fishes, and implications and uses in aquaculture and fisheries

“…In δ stage atretic follicles, granulosa cells are drastically reduced in number and they contain yellow and/or brownish pigments (lipofuscins and melanin) whose appearance shows species‐specific characteristics (Figure 2a,b). The autofluorescence properties of lipofuscin make atretic follicles at this stage easily recognizable from the surrounding connective stroma in unstained histological sections under florescence microscopy (Medina et al, 2021). If follicular cells accumulate melanin, δ atretic follicles can become morphologically similar to melanomacrophage centres (Figure 2b).…”

The development of the digestive system and the fate of the yolk syncytial layer in postembryogenesis of Stenodus leucichthys nelma (Teleostei)

“…We propose that both, nonprofessional and professional, phagocytes clear the YSL remnant in S. leucichthys nelma ; however, to test this proposition the phagocyte cell types need to be determined. The association of the YSL remnant and phagocytes resembles late atretic follicles with melanomacrophage centers (MMC) (Corriero et al, 2021; Medina et al, 2021). Melanomacrophages are observed in the kidney, liver, spleen and reproductive system of different teleost species (Campuzano‐Caballero & Uribe, 2014, 2017; Leknes, 2004; Patel et al, 2009).…”