Intensive production of the harpacticoid copepod Tigriopus californicus in a zero-effluent \u2018green water\u2019 bioreactor

Alfonso Prado-Cabrero,John M. Nolan,Rafael Herena-Garcia

doi:10.1038/s41598-021-04516-w

Abstract

Aquaculture is looking for substitutes for fishmeal and fish oil to maintain its continued growth. Zooplankton is the most nutritious option, but its controlled mass production has not yet been achieved. In this context, we have developed a monoalgal ‘green water’ closed-loop bioreactor with the microalgae Tetraselmis chui that continuously produced the harpacticoid copepod Tigriopus californicus. During 145 days of operation, the 2.2 m3 bioreactor produced 3.9 kg (wet weight) of Tigriopus with (dry weight) 0.79 ± 0.29% eicosapentaenoic acid (EPA), 0.82 ± 0.26% docosahexaenoic acid (DHA), 1.89 ± 0,60% 3S,3’S-astaxanthin and an essential amino acid index (EAAI) of 97% for juvenile Atlantic salmon. The reactor kept the pH stable over the operation time (pH 8.81 ± 0.40 in the algae phase and pH 8.22 ± 2.96 in the zooplankton phase), while constantly removed nitrate (322.6 mg L−1) and phosphate (20.4 mg L−1) from the water. As a result of the stable pH and nutrient removal, the bioreactor achieved zero effluent discharges. The upscaling of monoalgal, closed-loop ‘green water’ bioreactors could help standardize zooplankton mass production to supply the aquafeeds industry.

Highlights

As a consequence of a fast growth over the last 20 years, fed-aquaculture has recently outpaced non-fed aquaculture production of aquatic animals[1]
The work described here suggests that closed-loop ‘green water’ polycultures can help cross one of the biotechnological frontiers humans are still facing: The mass production of zooplankton
We have not measured dissolved oxygen and ammonia concentrations. These factors did not appear to affect the growth of Tetraselmis or Tigriopus, the continuous evaluation of these parameters will be essential in reactors in continuous operation

Summary

Introduction

As a consequence of a fast growth over the last 20 years, fed-aquaculture has recently outpaced non-fed aquaculture production of aquatic animals[1]. ‘green water’ aquaculture produces fish feed on site, but in addition, the rich biodiversity of these ecosystems protect farmed fish and shrimps against diseases, and maintains water quality in a way that minimizes the production of contaminated effluents[11]. Tetraselmis can grow in reused culture media[28] or even benefit from them[29] These characteristics make Tetraselmis an ideal candidate to inoculate a recirculated ‘green water’ culture to feed zooplankton and control the levels of ammonium and phosphate in the water. To the authors’ knowledge, this is the first report describing the use of the ‘green water’ technique to produce zooplankton in a controlled way This new concept has the potential to be scaled up to help substitute forage fish and contribute to the sustainable growth of aquaculture

Methods

Results

Discussion

Conclusion