Stable isotope and fatty acid analysis reveal the ability of sea cucumbers to use fish farm waste in integrated multi-trophic aquaculture.

Stable isotope ratios, carbon (δ13C) and nitrogen (δ15N), and fatty acids validated the trophic connection between farmed fish in a commercial nearshore fish farm and sea cucumbers in the Mediterranean Sea. This dual tracer approach evaluated organic matter transfer in integrated multi-trophic aquaculture (IMTA) and the ability of sea cucumbers to incorporate fish farm waste (fish faeces and uneaten artificial fish feed) into their tissue. Between October 2018 and September 2019, Holothuria (Roweothuria) poli Delle Chiaje, 1824, co-cultured at IMTA sites directly below one of the commercial fish cage , at 10 m and 25 m from the selected fish cage, and at two reference sites over 800 m from the fish farm. Sea cucumbers were sampled from each site in February, May and September, except at 0 m due to mass mortalities recorded here in the first month of study. Isotopic mixing models revealed that fish farm organic waste was the dominant dietary source for H. poli in IMTA at 10 m and 25 m from the cage. The contribution of marine plant-derived organic matter, Posidonia oceanica leaves and rhizomes, was least important. The isotopic signatures of sea cucumber tissues at reference sites were not explained by the sampled food resources. Importantly, fatty acid profiling revealed a high abundance of individual terrestrial plant fatty acids, such as oleic (18:1n-9), linoleic (18:2n-6) and eicosenoic (20:1n-9) acids in sea cucumber tissue at 10 m and 25 m from the fish cage, presumably linked to the terrestrial plant oil content of the fish feeds. At the reference sites, sea cucumber tissues were characterised by higher relative abundance of arachidonic acid (20:4n-6) acid, and the natural marine-based eicosapentaenoic (20:5n-3) and docosahexaenoic (22:6n-3) acids. These analyses revealed important differences in the composition of H. poli between the IMTA and reference locations, driven by aquaculture-derived waste near fish cages. Moreover, this study revealed temporal variation in food availability and quality, and possible differences in the physiological responses of H. poli. Stable isotope analysis and fatty acid profiling provided complementary evidence for the important dietary preferences of H. poli and validated the potential of sea cucumbers to uptake aquaculture organic waste as part of inshore fish-sea cucumber IMTA. It reveals the important implications that an established trophic link has on the viability of using sea cucumbers for the development of IMTA and the sustainable expansion of aquaculture.

Innovative Technologies to Promote Sustainable Recirculating Aquaculture in Eastern Africa-A Case Study of a Nile Tilapia (Oreochromis niloticus) Hatchery in Kisumu, Kenya.

Lake Victoria, regionally important both as a source of food and income, is under pressure due to overfishing and severe pollution. Currently, the vast majority of east African aquaculture is open-pond based. The adoption of modern and sustainable aquaculture technologies and practices-in this case study recirculating aquaculture systems (RAS)-will help the region increase food security and decrease its current reliance on imported fish and stressed wild stock. To this end, VicInAqua, a project under the EU Horizon 2020 program, has developed a pilot Nile Tilapia (Oreochromis niloticus) hatchery in Kisumu, Kenya using RAS adapted to local conditions. The hatchery is designed as a flexible, scalable, and modular system. An online monitoring system enables farmers to access farm data from both fish tanks and the supporting renewable energy systems, allowing around-the-clock monitoring and control. The hatchery is linked to a 14.3 kWp Photovoltaic (PV) system, including a 30 kWh Li-battery storage, to supply sustainable electricity. The water for the RAS, treated by a membrane bioreactor (MBR) and certified for use in aquaculture and agriculture, comes chiefly from Kisumu's municipal sewage, which reduces the farms' reliance on an expensive and occasionally intermittent potable water supply. Combining these technologies represents an industry first and offers a working example for larger-scale future developments. The purpose of the project is to demonstrate the possible technologies and practices in situ as well as provide a template for future development and investment. The hatchery is used by the Department of Livestock, Agriculture and Fisheries, Kisumu County, Kenya, as a training and demonstration facility to promote the aquaculture sector and increase the awareness, knowledge, and skills of fish farmers, as well as provide high quality fingerlings to cage farmers within the lake. Integr Environ Assess Manag 2020;16:934-941. © 2020 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).