Performance of a temperate-zone channel catfish biofloc technology production system during winter

Authors: Green, Bartholomew - Bart

Submitted to: Aquacultural Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/26/2014
Publication Date: 2/19/2015
Publication URL: http://handle.nal.usda.gov/10113/5356584
Citation: Green, B.W. 2015. Performance of a temperate-zone channel catfish biofloc technology production system during winter. Aquacultural Engineering. 64:60-67.

Interpretive Summary: Large numbers of fish can be stocked and fed intensively in the biofloc technology (BFT) production system because a complex of living organisms, including phytoplankton and bacteria, closely associated with particulate organic matter that is maintained in suspension in the water column by continuous aeration utilizes nitrogenous waste excreted by the fish. Channel catfish (Ictalurus punctatus) have been grown successfully in an outdoor BFT production system. Unlike outdoor BFT production systems in the tropics that are operated year-round, the channel catfish studies were conducted only during the growing season and BFT production tanks were drained and idled at harvest. If an outdoor BFT production system is to be viable at temperate latitudes, then data gaps related to system and fish performance over the winter must be addressed. In this study, conducted from mid-November through mid-April, almost all of the market-size channel catfish stocked survived, but lost a small amount of weight despite being fed when water temperature exceeded 60 degrees Fahrenheit. At harvest, fish appeared robust and healthy. Known quantities of ammonia added to tanks on several occasions during the winter were biotransformed completely, presumably by bacterial oxidation, known as nitrification, or by uptake by algae. The results of this experiment demonstrate that catfish will survive well through the winter in a BFT production system and that the system retains its ability to biotransform ammonia at low winter temperatures. This is important because biotransformation of ammonia will proceed without delay once intensive feeding of the fish resumes in the spring.

Technical Abstract: Channel catfish (Ictalurus punctatus) have been grown successfully in an outdoor biofloc technology production system. Outdoor biofloc production systems in the tropics are operated year-round, whereas the channel catfish studies were conducted only during the growing season and biofloc production tanks were harvested and idled for the winter. If an outdoor biofloc production system is to be adopted by farmers at temperate latitudes, then data gaps related to system and fish performance over the winter must be addressed. The present study was conducted to address these data gaps for channel catfish culture. Waters from a recently completed biofloc production experiment that contained low (153.3 mg/L) and high (790.0 mg/L) total suspended solids were retained for this study. Three 15.7-m3 tanks per water type each were stocked (8 kg/m3) with market size channel catfish from that same study for a 152-d study from November to April. Mean chlorophyll a concentrations were similar in both treatments during the first 55 days, after which treatments diverged and chlorophyll a concentration increased linearly (P < 0.001, R2 = 0.721) to a mean final concentration of 2,251.7 mg/m3 in the low solids treatment. Ammonia from ammonium chloride spikes (1.25-1.5 mg TAN) added on three occasions during the experiment was biotransformed completely, putatively by algal uptake and nitrification. Ammonia biotransformation rate was linearly related to mean water temperature in the high solids (P < 0.001, R2 = 0.920) and low solids (P = 0.002, R2 = 0.761) treatments. Catfish survival through the winter was high (99.75%) in biofloc tanks and did not differ significantly between treatments. Net fish yield did not differ significantly between treatments. However, net fish yields were 1-4% less than initial fish biomasses. Water in the biofloc production tanks appeared to retain through the winter the ability to biotransform ammonia regardless of whether phytoplankton or suspended solids predominate and despite sustained input of ammonia-nitrogen. Having an active biofloc in the spring obviates the start-up time required to establish a new, fully functional biolfoc and the associated TAN and nitrite spikes.