Hello! I`m rex-m, recirc expert MSc Matthias Mahnke. As an expert in aquaculture I offer design and consulting for fish farming in recirculating aquaculture systems (RAS) and flow-through systems.

For this, I have specialized in freshwater fish such as trout, char, sturgeon and caviar. I reject RAS projects for land-based marine fish farming and tropical aquaculture.

In the year 2015 I have founded my one-man business rex-m. As a freelancer I don’t sell any equipment. Instead, I offer following services and I guarantee to work on every task myself!

Proposal for the design of fish farms based on the basis of species-specific performance indicators, production capacity together with site factors.

Preparation of technical drawings, process diagrams, system descriptions, project calculations and parts lists for aquaculture systems.

Evaluation of RAS and project documents. Technology and process optimization. Assistance in the management of fish farms.

Professional experience

The water world has fascinated me since I was a child. 26 years ago the master`s degree program Fishery Science and Aquaculture allowed me to increase my passion. Since then, I have been working as fish farm operator, project engineer and project manager.

Fish farm management

Since 2022 I have been working as fish farm manager for Mohnen-Eifel-Forelle, Elmar + Udo Mohnen GbR. Trout and charr are produced in flow through systems at the Geseke site. Fingerlings are reared in the hatchery. Outside the salmonids grow in raceways. The system can be run as a partial RAS via a biofilter bypass.

The hatchery is stocked with fertilized eggs and fingerlings mostly from Mohnen`s own production. An artesian well is used to rear fingerlings. Outside the trout grow out in a 500 m long raceway system that is fed with brook water. If necessary, the raceway system can be run as a partial RAS via a biofilter bypass.

From 2018-2019 I was head of production for Kasperskian AG in Switzerland. The focus was on sturgeon broodstock and the production of ovulated caviar. Although I was able to significantly optimize the management of the fish stock, the RAS and the sewage treatment plant, my evaluation revealed serious deficiencies in the basic production planning, in the availability of well water and in the depuration system. The operation was consequently stopped, because product sales remained below expectations too.

During my time at UFT AG I was involved in the plant management of AquaOrbis Baerial GmbH from 2008-2010. I had eliminated the teething troubles of the RAS, trained the fish farm staff and took care of the aquaculture system and fish stock management. Due to better product quality and profitability, I had started to cultivate spawners in outdoor systems. Despite a change of operator, sturgeon and caviar are still produced on this basis in Jessen.

From 2003-2005 I was plant manager on a RAS designed by Fischtechnik Fredelsloh GmbH. For half a year I was the only employee and therefore on duty around the clock. The Aalfarm Domäne Voldagsen GbR mainly produced eel for the Dutch market. In 2004 the RAS was leased to Caviar Creator Manufaktur GmbH for sturgeon production.

Project management

From 2020-2021 I had been working as a project manager for tirolfisch M.H. GmbH.I did the engineering of aquaculture systems, water withdrawl and wastewater treatment, and a fish processing facility to produce trout and char. 

From 2013-2015 I worked as an aquaculture project engineer for EMF Lebensmitteltechnik und Anlagenbau GmbH. I was responsible for the detailed planning of RAS and the construction supervision and optimization of the Nigerian Aviation project, a large fish farm for the production of Nile tilapia and African catfish. 

I was employed as a fisheries biologist at United Food Technologies AG from 2006-2012. My area of responsibility included reaearch and development, numerous basic planning of RAS and the support of the project engineers and technical purchasing. Moreover I was involved in the construction supervision for the mega project Emirates Aquatech for sturgeon and caviar production in Abu Dhabi.