Title controoling DO at net pens for fish culture

Auto feeder

Net pens with auto feeders for culturing red sea bream,

Kusuura Bay, Kumamoto, Japan

red seabream net pen

Ten thousands of three-years old red sea bream were

reared in each net pen

In general, 10 to 20 tons of fish are cultured in the net pens for fish culture such as red sea bream, yellow tail, salmon, etc. They are fed every day, but only 10 to 20% of the feed are utilized for their growth. The other remaining parts are discharged to the surrounding environment of the net pens as food residues, faces, urine, etc., and consume DO of the water. Therefore, the reared fish in the net pens often suffer from unhealthy levels of decrease of DO of the water.

DO decrease in the net pen during night and its recovery with a micro-bubble generator

Aquanet 2009 DO data-E

An example of daily fluctuations of DO at the net pens that cultured red seabream in Kusuura Bay, Amakusa, Kumamoto, Japan. Modified from Tsutsumi (2009) Aquanet November, pp. 40-45.

Daily DO fluctuations of the water were observed at "Control net pen (12 m x 12 m x 8 m)". The DO of water around the saturated levels (about 7 mg/L) was kept during the daytime, since the amount of oxygen released from phytoplankton exceeds the oxygen consumption by the respiration of reared fish and food residues and feces. However, the DO of the water tended to decrease during the nighttime, due to the oxygen consumption by phytoplankton that cannot undergo photosynthesis. In particular, in the period of warm water between July and September, the fish reared in the net pens is often exposed to the insufficient DO conditions of less than 5 mg/L.

Recovery of DO of the water in the net pen by aeration of the water with micro-bubbles and its effects on fish farming

An all-in-one type of micro-bubble generator (eco-Bubble-400) was set at the depth of about 5 m at the center of the net pen, and worked for 15 hours between 5 p.m. and 8 a.m. of the next day, every day. In this net pen, the decrease of DO did not occur during the nighttime. The fish was reared around saturated DO conditions of the water throughout the day. Since it is not suffered from the unsuitable DO conditions during the nighttime, it can digest the feed, absorb its nutrients more efficiently, and grow faster. Tsutsumi et al. (2014) reported 42 % of growth acceleration of the body weight at the net pen which reared 3-years old red seabream by the aeration of micro-bubbles of the water with one set of eco-Bubble-400 during the period of the experiment for 108 days.

eco-Bubble aeration system for fish farming is able to resolve this short oxygen supply problem''

to the fish reared in net pens !