Ultrastructural changes in mitochondria during oogenesis in two phylogenetically close fish species

Area of Science:

• Ichthyology
• Cell Biology
• Reproductive Biology

Background:

• Oocyte development involves complex cellular processes, including yolk autosynthesis.
• Mitochondria play a crucial role in cellular energy metabolism and biosynthesis.
• Comparative studies of oocyte ultrastructure can reveal species-specific adaptations in reproduction.

Purpose of the Study:

• To investigate the ultrastructure of oocyte mitochondria in Sardina pilchardus and Engraulis encrasicolus.
• To determine the contribution of mitochondria to endogenous yolk autosynthesis in these species.
• To compare mitochondrial morphology and abundance during oocyte development.

Main Methods:

• Transmission electron microscopy was used to examine oocyte ultrastructure.
• Mitochondrial morphology, abundance, and cristae volume fraction were quantified.
• Comparative analysis was performed between developmental stages and species.

Main Results:

• Mitochondrial structure and abundance differed in secondary growth oocytes between sardines and anchovies.
• Sardine oocytes had a higher percentage of mitochondria, but smaller individual sizes, with increasing cristae volume fraction.
• Anchovy oocytes showed a higher percentage of mitochondria in early secondary growth, with decreasing cristae volume fraction initially.

Conclusions:

• Mitochondria in sardine oocytes are hypothesized to contribute to yolk granule formation.
• Mitochondria in anchovy oocytes are suggested to be involved in lipid synthesis pathways.
• Both species exhibit exogenous yolk heterosynthesis via pinocytosis.