USING MARINE FINFISH HATCHERY EFFLUENT TO GROW ULVA SP. IN A PILOT LAND-BASED IMTA SCHEME

SeaWheat ULVA: TOMORROW’S “WHEAT OF THE SEA”, A MODEL FOR AN INNOVATIVE MARICULTURE

TROIANOU1 E., ABATZIDOU1 E., TZOVENIS1,2 I.
1 Kefalonia Fisheries S.A., Livadi Lixouri, 28200 Kefalonia, Greece
2 Microphykos, Athens 15238, Greece
E-mail: e.troianou@kefish.gr
Abstract
Ulva sp. seedlings, collected from a nearby natural macroalgae bed, were used to initiate a land-based pilot seaweed aquaculture system. The algae were cultivated in translucent HDPE tanks, each with a capacity of 1 m³. Water from the sedimentation tank—the final stage of the biological water treatment process of the marine finfish hatchery at Kefalonia Fisheries SA—was continuously flowing through the tanks, supplying inorganic nutrients (NH₄-N, NO₃-N, NO₂-N, PO₄-P, etc.) with a residence time of 20 minutes.
This hatchery effluent originated from the treatment of runoff water from broodstock, larvae, and fry tanks used for rearing sea bass (Dicentrarchus labrax) juveniles before their transfer to offshore sea cages.
Ulva sp., introduced at an initial loading of 1 kg per m³, grew well in the effluent, which had an average concentration of 0.87 mg/L total dissolved inorganic nitrogen and 0.62 mg/L inorganic phosphorus. Since January 2025, the integrated multi-trophic aquaculture (IMTA) system using Ulva sp. achieved an average daily growth rate of 10.870% (±7.802%), with lower rates observed in spring (4.827%, ±2.438%) and higher rates in early summer (18.927%, ±1.812%).
The success of this pilot Ulva sp. cultivation—effectively contributing to both additional treatment of the hatchery effluent and biomass production—supports the planned scale-up to treat the full volume of the farm’s discharge. Discussions are currently underway regarding the use of the produced biomass as raw material for agro-industrial applications, such as biostimulants and biofertilisers.