GREENHOUSE GASES EMISSIONS IN A PRAWN HATCHERY SYSTEM
Greenhouse gases emissions increase global temperature, and consequently, cause climate changes. Since aquaculture is growing rapidly compared to other sectors on the food chain, studies focusing on gas emissions are important to understand greenhouse gases dynamics in different production systems, at all stages of production. In this context, we measured emissions of CO2 and CH4 in an indoor Macrobrachium rosenbergii hatchery system.
We used two rearing tanks (600L) to produce Macrobrachium rosenbergii post larvae. Tanks were composed with a simple modular closed system with biological filter and were stocked according to hatching rate of the eggs, causing an unintentional difference in stock density (Tank A ~7000 larvae and Tank B ~12000 larvae). Water temperature (29-30°C), aeration, salinity (12) and photoperiod (12h/12h) were maintained constant. Ammonia, dissolved oxygen and temperature were monitored daily. One meal of Artemia nauplii (4 nauplii/ml) and two meals of inert diet were supplied daily. Inert diet started after larval stage V and was adjusted according to development. Tank management was performed daily as well, but only during the day. One day before harvest (26 days after stocking) we measured carbon dioxide and methane emission or absorption at tanks surface at 15h (day) and 21h (night) using diffusive chamber method. Gases concentrations were obtained by chromatographic analysis.
We observed that all tanks emitted higher amount of CO2 during the day, drastically reducing at night. Both tanks emitted CH4, but during the night, Tank A assimilated while Tank B increased its emission (Table 1).
Daily management, such as feed and siphoning can increase the emissions once high rates were observed during the day. Besides, a higher activity of larvae and addition of Artemia nauplii at day can also increase the emissions. Stock density can be related to increased emissions since was observed high emission values in tank with higher density. Although we lack true replications that impede conclusive generalizations, we suggest that there are emissions of greenhouse gases in M. rosenbergii hatchery production and they cannot be overlooked.