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Aquaculture threatens natural resources by fishing down the sea to supply fishmeal. Alternative protein sources in aquafeeds can provide a solution, particularly those that are waste from other operations and thereby reduce feed production costs. Toward this goal, we examined the waste biomass of marine periphyton from biofilters of an integrated multi-trophic aquaculture (IMTA) system as a replacement for fishmeal in diets of gilthead seabream (Sparus aurata). Four isoproteic (41%) and isolipidic (16.7%) aquafeeds were formulated with increased content of periphyton and a corresponding decrease in fishmeal from 20 to 15, 10, or 0%. The growth and biochemical content of seabream fingerlings (initial body weight 10 g) were examined over 132 days. Replacing 50% of fishmeal by waste periphyton improved feed conversion ratio (1.2 vs. 1.35 in the control diet) without harming fish growth. The complete replacement of fishmeal with periphyton resulted in 15% slower growth but significantly higher protein content in the fish flesh (59 vs. 52% in the control diet). Halving fishmeal content reduced feed cost by US$ 0.13 kg -1 feed and saved 30% in the cost of conversion of feed to fish biomass (US$ 0.58 kg -1 produced fish vs. $0.83 in the control diet). Finally, the total replacement of fishmeal by waste periphyton in the diet reduced the fish in-fish out ratio to below 1 (0.5-0.9) as compared to 1.36 in the control diet. Replacing fishmeal with on-farm produced periphyton minimizes aquaculture footprint through the removal of excess nutrients in effluents and the use of waste biomass to reduce the 'fish in' content in aquafeeds and fish production costs. The present study demonstrates the great practical potential of this dual use of marine periphyton in enhancing the circular economy concept in sustainable fish production., (© 2021. The Author(s).)

Periphyton-based biofilters for aquaculture effluent possess multiple advantages, in water oxygenation, CO 2 reduction and production of useful biomass. The performance of a marine periphyton biofilter, in terms of uptake rate and efficiency in removing different forms of nitrogen, was investigated. A periphyton biofilter was paired with an upstream macroalgae biofilter stocked with Ulva to expose the periphyton to ammonia-depleted but nitrate-rich effluent. Three trials compared the removal of total ammonia-N (TAN), nitrate (NO 3 -N), total N and phosphorus. The biofiltration and growth performance of (1) the periphyton downstream to the Ulva tank, (2) periphyton alone and (3) Ulva alone were compared. Biofiltration performance was evaluated at different areal loads of TAN and NO 3 -N. Periphyton growth performance did not depend on the effluent nutrient composition or on N loads, and yielded between 7.3 and 10.6 g dry weight m −2  d −1 . While the Ulva preferred uptake of TAN over NO 3 -N, the periphyton showed no preference between them , demonstrating flexible shifts between TAN and NO 3 -N uptake. TAN uptake rate by the periphyton was not influenced by the effluent composition. However, periphyton NO 3 -N uptake rate and efficiency rose about fivefold, up to 1.4 g NO 3 -N m −2  d −1 and 63%, respectively, upon depletion of TAN areal load below 0.18 g N m −2  d −1 (<0.3 mg L −1 ) by the Ulva pre-treatment. Normalizing nutrient uptake rate to biomass revealed similar uptake rate of TAN and phosphorus by periphyton and Ulva , while the periphyton took up nitrate much faster. By removing up to 76% of the total nitrogen, with specific removal efficiency of 97% of the TAN and of 67% of the NO 3 -N, the novel dual Ulva -periphyton biofilter revealed a synergistic potential in treatment of nutrient-rich mariculture effluents. [ABSTRACT FROM AUTHOR]

A periphyton biofiltration system of mariculture effluents was studied to identify ecological processes and management procedures that strongly affect the biofilter functioning, in order to attain optimal biomass production and nutrient removal. The multivariate statistical technique of factor analysis allowed reducing the large amount of data available into three main factors. The first factor, which accounted for 49% of the overall data variability, was herein called "biological activity" as it represents the joint effects on the variables measured of photosynthesis, N and P uptake, respiration and decomposition of organic matter. The second and third factors were "autotrophic biomass density" and "nitrite and phosphate uptake/release balance", which, respectively, accounted for further 20% and 14% of the data variability. A conceptual model, describing the functioning of the periphyton biofilters, revealed a delicate equilibrium among the different processes, whose understanding help to manage the biofilters towards optimal production of periphytic biomass and nutrient removal. Raising flow rate raised the overall nutrient uptake rate but reduced uptake efficiency and diluted nitrifying particles. A reduced flow rate led to sedimentation of organic particles, decomposition and nutrients re-mineralization. Apparently, control of water flow and nutrient content, periphyton substrate area and the cleaning of the effluent supply system are key management elements for the operation of a periphyton-based biofilter system that maximizes both periphyton biomass production and nutrient removal. [ABSTRACT FROM AUTHOR]

Cost of effluent treatment, water quality maintenance and feeds constitute most of aquaculture's operational costs, and influence its sustainability. The present study examined the effectiveness of periphyton for biofiltration of mariculture effluents. Marine periphyton was allowed to spontaneously develop on a plastic net substrate, in experimental bioreactors that were fed with effluents from fish mariculture ponds. Biomass development and nutrient uptake were followed over four seasons. Attention was given to the orientation and area of the net substrate, season and additional operational factors. The highest specific growth rate (SGR) of 27% day − 1 was measured during the second week of periphyton growth in the summer. Mean daily periphyton production rates in the spring and autumn were 2.4 and 1.8 g (ash-free dry weight) m − 2 day − 1 , respectively. The vertical orientation of the net substrate was overall advantageous over the horizontal orientation. Increasing the substrate area of vertically oriented nets in the biofilter increased the removal efficiency of total ammonia nitrogen (TAN) up to 80%, and allowed more biomass production in the biofilter. Multiple polynomial regression models suggest strong effect of biomass weight and effluent retention time on the removal efficiency of TAN and dissolved inorganic nitrogen (DIN). The removal rates of TAN and DIN in these experiments were between 0.11 and 1.2 g N m − 2 (substrate area) day − 1 for periphyton at the age of 7 and 42 days, respectively. Marine periphyton seems to be a simple, low cost and sustainable component, which can perform biofiltration/rehabilitation of water quality and potentially serve as feed for fish and shrimp. [ABSTRACT FROM AUTHOR]

Correction to: I Scientific Reports i https://doi.org/10.1038/s41598-021-00466-5, published online 25 October 2021 The original version of this Article omitted an affiliation for Amir Neori. Morris Kahn Marine Research Station, Marine Biology Department, The Leon H. Charney School of Marine Sciences, University of Haifa, 3498838 Haifa, Israel The Interuniversity Institute for Marine Sciences in Eilat, 8810302, Eilat, Israel The original Article has been corrected. [Extracted from the article]

Biofilters made of Ulva and periphyton differ in their effectiveness in removing ammonia and nitrate from mariculture effluents. Our research evaluated the practicality of a combination of these two biofilters in improving the overall removal of dissolved N, where efficient removal of ammonia by the seaweed is followed by efficient removal of nitrate by periphyton. A paired Ulva -periphyton biofilter was exposed to various areal loads of ammonia and nitrate, the primary nitrogen forms in fishpond effluents. A first upstream macroalgae biofilter stocked with Ulva was fed with fishpond effluents at different areal loads of ammonia and nitrate, while a second downstream periphyton biofilter was paired for further nitrogen removal from the effluent. Ulva removed ammonia at a rate of 0.7–5.4 g TAN m−2 d−1, in correlation with the TAN areal load, with V max of 5.1 and K m of 4.4 g TAN m−2 d−1. Downstream periphyton was exposed to a lower TAN, but nitrate-rich effluent, and revealed similar capacities for the removal of both N forms, at removal rates of up to 1.7 and 1.8 g N m−2 d−1, respectively. Compared to nitrate, areal load of TAN had a greater impact on the removal dynamics of both N forms by periphyton. Overall, the paired biofilter resulted in a nearly total depletion of ammonia (97%) and efficient nitrate removal (67%), when areal loads in fishpond effluents were below 2 and 4 g N m−2 d−1 of TAN and NO 3 -N, respectively. • Ulva- periphyton biofilter removed 97% of TAN & 67% of NO 3 -N in fishponds effluent. • <2 g TAN and 4 g NO 3 -N (m−2 d−1) in effluent resulted with maximal removal. • Ulva removed TAN in correlation with areal load of this nutrient. • Periphyton revealed similar capacities for the removal of TAN and NO 3 -N. • Areal load of TAN had great impact on periphyton removal dynamics of TAN & NO 3 -N. [ABSTRACT FROM AUTHOR]