Developing a feeding protocol for grow-out Atlantic halibut based on growth, physiological and behaviour responses to feeding frequencies

Atlantic halibut have been a part of Norwegian aquaculture since the 80s, but due to its complex biology, it has been proven challenging for the halibut farmers to succeed commercially. One of the industry?s remaining challenges is the slow growth of the fish during the grow-out phase, which is thought to be mainly due to its lack of appetite/feed intake. Feeding fish in aquaculture is a complex process, since the farmer must balance overfeeding and underfeeding to obtain the best fish growth and at the same time limit negative impacts on water quality and the environment. When food is abundant, food intake is limited, in between other factors, by the capacity of the stomach. The digestion and passing of food throughout the digestive system is affected by several factors including fish size, meal size and food quality. As the food is digested, and the stomach empties, the motivation to resume feeding increase. Thus, knowing the food transit time across the digestive system is valuable information to determine the time to the next meal, and design an optimal and knowledge-based feeding strategy. To determine how much and how often halibut should be fed, this project will investigate how different feeding frequencies affect the fish growth, behaviour, appetite, digestion and fillet quality, and the water quality. As a first approach, the project will determine the food transit speed across the digestive system, and based on these results, different feeding frequencies will be timed to the stomach emptying in a small-feeding trial. The best feeding frequency will be tested and validated at a commercial-scale trial. The results generated in this project will be summarized to develop a new feeding protocol for Atlantic halibut farmers that will promote a more successful and sustainable production of this species. Preliminary data show that 1 kg sized halibut, held at 9 degrees celsius evacuate 70 % of stomach content after a big meal, and a total gut clearance time between 96 and 120 hours. Over time 2 kg sized halibut, fed every single day or every third day, consumed equal quantities of feed.

Feeding is one of the most fundamental aspect of rearing animals, as the farmed animal must grow in order to turn a profit. Slow growth of Atlantic halibut (Hippoglossus hippoglossus) above 1kg (grow-out) is viewed by halibut farmers as one of the remaining bottlenecks hindering growth in the industry. The development of optimized feeding strategies for grow-out halibut will therefore contribute to increase growth rates, minimize feed waste and reduce production cost. This has the potential to advance Atlantic halibut farming towards a more sustainable, economical viable and competitive aquaculture industry. Thus, this project will address current knowledge gaps regarding optimal feeding strategies for grow-out Atlantic halibut. The main goal of the PhD project is to determine how different feeding strategies can affect feeding behaviour, appetite, food intake and digestive performance, and identify the best-suitable feeding strategy which results in an improved growth and reduced food waste in grow-out Atlantic halibut. It will be important to investigate the gastrointestinal transit time in Atlantic halibut (WP1), as food intake is generally limited to the stomach capacity, and the time for the next meal limited by gastric evacuation time (GET). This will provide valuable information to design an optimal feeding regime regarding feeding frequency. The optimized feeding regime based on GET, will be further explored in terms of impact on water quality, feeding behaviour, migration patterns, performance, appetite control, digestibility, and fillet quality in a small-scale feeding trial (WP2). Finally, the effect from the optimized feeding regime will be assessed in a commercial large-scale rearing scenario as opposed to standard feeding protocols (WP3). The main findings will be available to the end-users and public through the planned peer reviewed articles and industry feeding protocol (WP4).