The white spotted pufferfish in the Japan seas is a small fish, but the males of the species create large, intricately engineered nests in the seafloor with its body. These designs draw females to mate, and it is thought that the shape of the nest accumulates very fine sand at the center in order to give the eggs the best chance for survival. 

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"Males of the pufferfish, Torquigener albomaculosus Matsuura, 2014, are known to construct a nest surrounded by radially aligned peaks and valleys on sandy seabeds, which plays an important role in female mate choice. Here, we report the spawning and parental egg care behavior by the pufferfish based on underwater observations. Pufferfish spawning occurred from spring to summer. Although semi-lunar mating and hatching were observed in the latter period of the spawning season, their periodicity was not consistent throughout the spawning season. Females visited males’ nests on the sandy bottom, and males courted them by stirring up sand in the nest and performing a rush and retreat behavior. The females and males mated in pairs, releasing gametes on the nest within approximately 1 s. They mated repeatedly until females left the nest. The males mated with other females on the same day. After matings, males stayed at the nest site and cared for the eggs deposited on the sandy bottom until hatching; males flapped their fins to stir the eggs on the bottom, and drove away fishes that passed close to the nest site. Hatching occurred synchronously with the male flapping behavior around sunset. The reproductive ecology of T. albomaculosus is unique in its paternal egg care and mating system of male-territory-visiting polygamy, and this is the first record of this behavior in marine pufferfishes." (Kawase et. al) 

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Sources: 

 

Shameem, Abdulla Jailam, Manousos Valyrakis, and Hossein Zare-Behtash. 2021. "A Fluid Dynamics Approach for Assessing the Intelligent Geomorphic Design of the Japanese Pufferfish Nest" Geosciences 11, no. 1: 22. https://doi.org/10.3390/geosciences11010022

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​Kawase H, Okata Y, Ito K, Ida A. Spawning behavior and paternal egg care in a circular structure constructed by pufferfish, Torquigener albomaculosus (Pisces: Tetraodontidae). Bulletin of marine science. 2014;91(1):33-43. doi:10.5343/bms.2014.1055

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