Technical optimisation of zinc supplementation strategies for enhancing zinc availability, improving fish health and minimising environmental impact

Background

Zinc is essential to maintain good barrier function in the skin, intestine and gills, osmoregulatory functions, wound healing, bone health and functioning of several proteins at the molecular level. Increasing use of plant-based ingredients in Atlantic salmon feeds has reduced the level and availability of zinc from fish feed, thereby increasing dieatry levels needed to meet the requirement.

Salmon requirements

The Zn requirement for Atlantic salmon parr was estimated to range between 37 – 60 mg/
kg. However, in commercial salmon feeds with high inclusion of plant ingredients, total dietary Zn levels of 140 – 160 mg/kg feed is required for freshwater parr and 200 – 240 mg/kg for seawater post-smolts. Further, improved health and welfare effects on cataracts, wound healing and barrier functions have been demonstrated at increased total Zn levels up to 300 mg/kg.

Increasing total Zn levels for health benefits in feed reduces availability and retention, due to reduced marginal effeciency at high inclusion levels, and ultimately increasing Zn emissions. Estimations from the recent Atlantic salmon production data reveal that
only 15% for Zn fed through the diet is retained in the fish, rest being lost to the environment. Increased Zn emissions can lead to risk of toxicity for marine organismes and development of multiresistance bacteria in the marine environemnt.

Legislation

Accordingly, to prevent negative environmental impact, the European Commission (EC) legislation on animal feeds has set a maximum limit of 180 mg Zn/kg in salmon feeds, implemented in 2016 following the EFSA feed additive panel recommendation reducing it from the former limit of 200 mg/kg feed. Further reduction to 150 mg/kg has been suggested by EFSA and an evaluation of the environmental impact is currently underway, the outcome of which can result in further reduction of Zn limit in salmon feeds.

Goal

Changing feed composition, increasing dietary needs, declining fish health and welfare, feed legislative limitations, and potential negative environmental impacts have increased the need for improved utlisation of dieatry zinc. Therefore, strategies to increase zinc
status of salmon without increasing total Zn levels in feeds should be prioritized i.e. improving dietary Zn availability.

The goal of the project is to improve zinc availability in salmon feeds such that more dieatry zinc is retained in the fish for better health benefits, ultimately reducing the emisions to the environment.

This is what we do

In TOP-Zinc, we propose to optimise novel top-coating technologies for zinc (WP1), and use of a novel phytase enzyme and with compare conventional methods (through premix) to improve dietary Zn availability and status in salmon post-smolts (WP2). Further, the impact on fish health (WP3) and potential environmental risks associated (WP4) will be assessed culminating in a long term validation trial in sea cages (WP5).

Contact

Antony J. Prabhu Philip

Senior Scientist
+47 55 50 12 05