Control of dissolved oxygen levels of water in net pens for fish farming by a microscopic bubble generating system

Abstract

A microscopic bubble generating system (MBGS) has been developed to control dissolved oxygen (DO) levels suitable for fish farming. The MBGS has been tested to confirm its capability in net pens. Water conditions in a fish farm were monitored every two hours from June to October 2004 by setting an online vertical profiling system (OVPS) close to the net pen. DO in the net pen water decreased to physiologically stressful levels for the fish during the night (4.84-5.51 mg/L), while the DO was kept in saturated conditions during the day, due to oxygen supply from phytoplankton. The MBGS was operated from the evening to the morning of the next day for 16 h, to successfully create DO-saturated conditions in the net pen water at night. By using microscopic bubbles during the warm seasons, DO levels in the net pen water could be improved to a level suitable for fish farming. However, the low DO levels (<5.0 mg/L) of the bottom water occasionally extended to the net pen layers, despite the supply of microscopic bubbles to the water. To maintain the DO of the net pen water at levels suitable for fish farming, DO supply to the net pen water and the bottom water needs to be increased, and the organically enriched sediment just below the net pens needs to be treated.KEY WORDS: dissolved oxygen, fish farming, microscopic bubble, online vertical profiling system, red sea bream.

Increase in Alphaproteobacteria in association with a polychaete, Capitella sp. I, in the organically enriched sediment

“…The density of Capitella sp. I tends to recover naturally during the autumn to winter, when oxygen-rich water is supplied to the bottom layers by the vertical mixing of the water, and consequently oxidized conditions are formed in the surface layer of the sediment (Tsutsumi and Kikuchi, 1983;Tsutsumi, 1987Tsutsumi, , 1995Tsutsumi, 1990;Srithongouthai et al, 2006). In this study, ORP of the surface layer of the sediment (up to a depth of 2 cm) at Stn -2 by January 2006, since the organic matter discharged from the net pens, such as feces of reared fish and food residues deposited on the sea floor intensively just below the net pens due to vertical mixing of the water .…”

Marine cage culture and the environment: effects on water quality and primary production

“…Thus, proper siting of farms in areas with sufficient flushing rates is recommended. Oxygen bubblers (Srithongouthai et al 2006, Endo et al 2008, mechanical aeration (Goldburg & Triplett 1997) and lowering sea cages below the ocean surface (Dempster et al 2009) are management tools that can be implemented on farms to minimize or eliminate dissolved oxygen depletion, but may not be feasible at remote ocean sites due to lack of electricity.…”

Investigation of some veterinary drug residues in sea water, sediment, and wild fishes captured around fish farms in the Aegean Sea: Oxytetracyline, ivermectin and emamectin

“…Lower amounts could be due to a pollution related to the excessive algae growth caused by phosphorus and is a major stress for fish (4). Dissolved oxygen threshold for healthy farms have a value over 4.0 mL/L; where as levels below 2.5 mL/L are considered to be critical (1,25). Water temperature is important because it not only establishes the maximum oxygen-holding capacity of water, but also has direct influence on rates of biochemical reactions and transformation processes occurring within the water column and in the sediment bed (4).…”