Developmental and Seasonal Changes in Lipid Droplets and Fatty Acid Composition in the Ovary and Liver of Female Spotted Scat (Scatophagus argus)

TL;DR

This study tracks how fat and fatty acids in the ovaries and livers of spotted scat fish change over a year, showing seasonal patterns linked to reproduction.

Contribution

The study reveals seasonal lipid dynamics and fatty acid shifts in spotted scat, linking liver storage to ovarian development.

Findings

Ovarian maturation peaks in summer with increased lipid droplets and fatty acids.

Liver accumulates lipids in winter and spring, likely storing energy for reproduction.

Liver plays a key role in transferring n-3 fatty acids to the ovaries before breeding.

Abstract

Reproductive success in fish depends strongly on the availability and distribution of energy reserves, particularly lipids and fatty acids. In aquaculture, understanding how these nutrients change during ovarian development is essential for improving broodstock management. In this study, female spotted scat were sampled every two months over the course of one year to examine changes in ovarian development, lipid droplet accumulation, and fatty acid composition in the liver and ovaries. The results showed that ovarian maturation occurred mainly in summer, accompanied by a marked increase in lipid droplets and fatty acids in the ovary. In contrast, lipid droplets and fatty acids accumulated in the liver during winter and spring, suggesting energy storage before reproduction. These findings suggest that the liver plays an important role in storing and supplying fatty acids for ovarian development. This study provides useful information for improving nutritional strategies and reproductive management of female spotted scat in aquaculture.

The spotted scat (Scatophagus argus) is a fish species widely distributed in Indo-Pacific waters. In China, females are preferred for aquaculture due to their faster growth rates. Reproduction in teleost fish requires substantial energy, primarily in the form of lipids and fatty acids, which are closely linked to reproductive success and ovarian development. In this study, female spotted scat broodstock were sampled bi-monthly from May 2019 to March 2020 to examine annual ovarian development, lipid droplet accumulation, and fatty acid composition in the liver and ovaries. Body weight, total length, standard length, and condition factor (CF) increased gradually over the sampling period. In July 2019, the gonadosomatic index (GSI) increased significantly, all ovaries reached stage IV, and lipid droplet accumulation was most pronounced. Ovarian saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), n-3 polyunsaturated fatty acids (n-3 PUFA), and n-6 PUFA reached their highest levels in July, whereas the ovarian n-3 PUFA/n-6 PUFA ratio was highest in May. The hepatosomatic index (HSI) was significantly higher from November to March than from May to September. The viscerosomatic index (VSI) was significantly elevated from November to March and in July. Liver lipid droplet accumulation was lowest from May to July. Absolute contents of liver SFA, MUFA, and n-6 PUFA were significantly higher in January and March than in May and July, while liver n-3 PUFA content and the n-3 PUFA/n-6 PUFA ratio peaked in May. These findings indicate that the peak breeding season of spotted scat occurs around July in southern China. From winter to spring, lipids accumulate in the abdominal cavity and liver, likely serving as energy reserves for subsequent ovarian development. The liver appears to play a key role in the uptake and transfer of n-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA) to the ovaries prior. This study provides useful insights into the reproductive physiology of spotted scat and supports improved broodstock management in aquaculture.

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