CAPTURE AND RE-USE OF FISH WASTES FROM IN-POND RACEWAYS

In pond aquaculture, fish wastes can be a limiting factor in production intensification.  If fish manure or any uneaten feed can be removed from the pond environment, then fish production should be able to be increased. This project had several objectives: 1) develop an in-pond raceway system (IPRS) solids capture and removal apparatus and employ it on a floating in-pond raceway system; 2) capture/harvest wastes from catfish grown in the IPRS units; 3) characterize the nutrient "waste" by-product collected; and 4) quantify the amount of dried fish waste collected when guar gum is added to the feed versus when it is not added.

We equipped 8 floating IPRS systems with fish manure harvesting gear and installed solids holding vessels in the pond adjacent to the test IPRS raceway units. Solids removal ports and plumbing were installed and a semi-solids pump was installed for solids collection and removal.  This pump lifted the collected water and solids slurry onto truck mounted tanks for transport to the next test arena (settling tanks) where characterization of the nutrient solid "waste" by-product and evaluation of its relative quantity and value with and without guar gum as a binder was conducted. Feed was milled containing the guar gum binder (0.03%) to increase solids capture of fish fecal solids during their culture. There was a control diet (without guar inclusion) as well for comparison. The goal was to determine guar gum effectiveness in consolidating or binding especially small post-digestion feed particles for enhanced efficiency in fish waste/nutrient collection, removal and used in additional value added research, such as its use in plant production and digestion for bio-gas energy production.

Feed trials using guar amended and control (non-guar) 32% protein floating feed were run from August 3 through November 3, 2016. Quantification of the fish waste was conducted through settling tanks and volume measurement followed up with drying a known volume of settled waste and extrapolating that to the total settled waste amount allowed for a total weight of the waste to be calculated.  This weight divided by the dry weight of feed fed provided the percent of solids captured. This was done for the regular (control) feed and the guar supplemented feed for comparative evaluation of the guar supplement.

After weekly collection of fish waste ended solids analysis revealed an overall average total solids (TS) content of 38 g/L and an overall volatile solids (VS) content of 32 g/L. Furthermore, after comparing both TS and VS contents for feed with guar added verses feed without guar added, preliminary examination of results indicates that the difference in feed type had no significant impact on solids collected using this particular system. Feeding rate and temperature were shown to have the greatest effect on both TS and VS contents. It was also discovered that due to the nature of the solids collection device (short quiescent zone), actual average solids content of recovered waste may be closer to 10%. This is currently being reevaluated and will be further discussed during the presentation.