Establishing optimal broodstock sex ratios for the royal gramma (Gramma loreto) in small scale system aquaculture

Abstract

The royal gramma (Gramma loreto) is vulnerable to anthropogenic impact in its coral reef habitats, and is deemed an “indicator” species of pollution. It is also heavily fished for the aquarium trade, being among the top 1% of imported marine aquarium fish species into the U.S. The objective of this study was to establish optimal sex ratios of broodstock groups for aquaculture as an alternative to wild capture, while balancing territorial aggression. Three two-month breeding trials were carried out in six 23 L aquaria stocked with one male and one, two, or three females. During the trials, each aquarium was filmed weekly for one hour at first light to record courtship, nest use, and aversive behaviors. Behaviors were quantified with JWatcher software and analyzed in repeated measures ANOVAs. Results suggest that in small aquaria, a sex ratio of one male to two females may be optimal for spawning because courtship and nest use behaviors are optimized while aversive behaviors are moderated. Past efforts to aquaculture the species have typically been conducted at broodstock sex ratios of 1:1. These results offer the potential to increase productivity of commercial aquaculture of the species.