Using a passive solar greenhouse with water tanks in overwintering of juvenile sea cucumber Apostichopus japonicus

The present work investigated the overwintering of juvenile sea cucumber Apostichopus japonicus which used a renewable energy system. The experimental period ranged from December 2023 to February 2024. Seawater, benefited from a temperature rise of about 3 °C in an underground pond, was pumped into 3.6 m³ plastic tanks on a rooftop greenhouse of a single-story building and heated by solar radiation. There were 56 such tanks in the greenhouse - half of them (28) were placed close to the south-oriented plastic film and the other half near the north-oriented wall. Those 28 tanks were subdivided into 4 groups of 7 tanks. Each group was heated for 4 days before the content was drained into the sea cucumber culture tanks of 10 m³ placed on ground floor of the building. For those 4 days of winter the water in the tanks was heated to an average of 15–20 °C in the south and 10–15 °C in the north. The culture tanks were divided into two groups to correspond to the south and north tanks and throughout the winter the average water temperatures were maintained at 16 ± 3 °C and 12 ± 3 °C respectively. The numerical experiments confirmed that if the greenhouse is developed into a double-plastic film greenhouse, the temperature of the tanks can be raised to 20.8 °C in the south and 16.4 °C in the north for 4 days even in the lowest atmospheric temperature. The three-month experiment witnessed the increase of average body weight of juvenile sea cucumber from 0.7 to 4.2 g along with its survival rate of 94.8 % and specific growth rate of 1.87 %d⁻¹. This indicates that the passive solar greenhouse has a great potentiality to reduce energy demand of animal houses using electricity or coal in winter.