Floating faeces for a cleaner fish production

Abstract

Recent developments in European recirculating aquaculture systems suggest expanding potential for this extremely water-efficient technique. However, the technology still faces challenges due to concerns over economic efficiency and system stability-both essential in minimizing the risk of financially and environmentally expensive failures. One key factor in maintaining stable production conditions in a recirculation loop is the effective removal of solid waste, i.e. fish faeces. This study tested a novel approach for solid control and demonstrates the value-adding potential of floating faeces under commercial conditions in a semi-recirculating fish farm in Germany. A commercial control diet was compared with an experimental diet in which the addition of 2.5% cork granules led to the production of floating faeces. Physiological assays indicated no pathologic tissue alterations associated with the experimental feed, and growth, survival and feed conversion were unaffected. Average single-pass removal by a specially developed surface separator accounted for 78.3% of floating solids, which accounted for 35.4% of total system solids. Total ammonia nitrogen concentrations in production water were roughly halved, from about 0.95 mg l −1 in the control to 0.47 mg l −1 using the cork diet, an improvement that in practice allowed a doubling of production on the same available water flow. This study shows that the application of floating faeces facilitates rapid and cost-effective removal of suspended solids, resulting in a considerable decrease of nutrient load in system and discharge water of the investigated farm.

Cork and guar gum supplementation enhanced the buoyancy of faeces, and protease supplementation alleviated the negative effects of dietary cork on growth and intestinal health of tilapia, Oreochromis niloticus × O. aureus

“…The difference might be concerned with the species of cork. The cork used in the study of Unger et al () was Q. surber and Q. variabilis in this study. Generally, Q. suber has higher suberin content and cell number, lower density and smaller hardness than Q. variabilis (Lei, Liu, Zhou, & Zhao, ; Liu, Lei, Zhou, Zhao, & Shi, ; Miranda et al, ; Zhang, Lei, & Chang, ).…”

“…During the feed processing, dietary cork still kept its original physical properties for its flexible and elastic properties (Unger & Brinker, ). When rainbow trout was fed diet containing 25 g/kg cork granules (0.5–1 mm), the average single‐pass removal by a specially developed surface separator accounted for 78.3% of floating solids and 35.4% of total system solids (Unger et al, ). In this study, dietary cork (20–40 g/kg) also generated floating faeces, but the highest floating faeces ratio (25.9%) was less than the report of Unger et al ().…”

“…When rainbow trout was fed diet containing 25 g/kg cork granules (0.5–1 mm), the average single‐pass removal by a specially developed surface separator accounted for 78.3% of floating solids and 35.4% of total system solids (Unger et al, ). In this study, dietary cork (20–40 g/kg) also generated floating faeces, but the highest floating faeces ratio (25.9%) was less than the report of Unger et al (). The difference might be concerned with the species of cork.…”

“…The study of Unger and Brinker () showed that the cork supplementation (20 g/kg) in the diet of rainbow trout ( Oncorhynchus mykiss ) created a low faecal density and a high ratio of floating faeces. Rainbow trout fed a cork‐supplemented diet (25 g/kg, 0.5–1.0 mm) also showed a high ratio of floating faeces (Schumann, Unger, & Brinker, ; Unger, Schumann, & Brinker, ), and the growth was not adversely impacted by cork supplementation (Schumann et al, ).…”

Generation, characterization, perniciousness, removal and reutilization of solids in aquaculture water: a review from the whole process perspective

“…Subsequently, the application of floating faeces has been shown to be a feasible method for the rapid and cost‐effective removal of suspended solids in a land‐based semi‐recirculating rainbow trout farm (Unger et al . ). Shortly afterwards, Schumann et al .…”