Physical feed quality and starch content causes a biological response in Atlantic salmon (Salmo salar L)

Tor Andreas Samuelsen,Marie Hillestad,Hans Jákup Jacobsen,Tor Johannes Hjertnes,Hanne Jorun Sixten

doi:10.1016/j.aqrep.2021.100791

Tor Andreas Samuelsen, Marie Hillestad + Show 3 more

Open Access

https://doi.org/10.1016/j.aqrep.2021.100791

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Abstract

The aim of this study was to investigate the effect of starch content and pellet physical quality on the biological response in Atlantic salmon. Salmon feeds with a large variation in physical quality were produced by the adjustment of dietary starch inclusion (92 g kg−1 or 64 g kg−1), preconditioner oil (0.0 or 11.0 kg h−1), extruder moisture addition (13.5 or 27 kg h−1) and drying temperature (38 °C or 70 °C). The variables impacted physical quality for the 12 feed codes and with hardness S (standing) and Durability measured in the range of 39–212 N and 39–94 %, respectively. Gently dried feed (38 °C) was harder and more durable than conventionally dried (70 °C). This could be explained by the phase transition theory and drying in the mobile rubbery phase above the glass transition temperature (Tg) for the gently dried feed codes. All feed codes were evaluated in Atlantic salmon performance and digestibility trials. There was a significant difference between the codes for weight gain (%; P < 0.001), specific and thermal growth rate (P < 0.01) and protein efficiency ratio (P < 0.01). Growth was negatively associated with increased starch content, hardness and durability parameters and reduced solubility, fat content and gross energy. The most important physical properties affecting growth performance were Hardness S, Durability and Doris dust, parameters that may represent feed hydration- and dissolution rates. This study documents that the impact of pellet physical quality should be considered when evaluating the results from biological fish trials.

Highlights

Extruded feed used in modern aquaculture production must be of a consistent and high physical quality to avoid crushing during transport, bulk storage and pneumatic feeding (Aas et al, 2011; Aarseth et al, 2006)
To avoid floating feed or fat leakage, oil adjustment in the vacuum coating process had to be performed resulting in deviation in proximate lipid content between the pellet codes (Table 3) and with GE content positively correlated to the lipid content (r2 = 0.87)
All responses were significantly different for the experimental codes except for solubility Dry matter (DM), fat and ash (Table 4)

Summary

Introduction

Extruded feed used in modern aquaculture production must be of a consistent and high physical quality to avoid crushing during transport, bulk storage and pneumatic feeding (Aas et al, 2011; Aarseth et al, 2006). Bogevik et al (2021) concluded that pellet who disintegrated slowly in water prolonged the gastric evacuation rate, and reduced feed intake in Atlantic salmon. This is in line with other published studies that have concluded that dry feed passed the gut slower than either soaked or less water stable feeds, and that soaked feed gave a significantly higher feed intake (Aas et al, 2011b, 2017, 2021; Oehme et al, 2014). Salmonids have a limited capacity to digest starch (Krogdahl et al, 2004), and energy originating from starch brings less digestible and metabolic energy than from lipid sources (National Research Council (NRC, 2011) Due to these metabolic limitations in the utilization of starch the feed manufacturing industry reduces the inclusion level of starch sources to a minimum without compromising physical feed quality. Pea (0.8 %), tapioca and other carbohydrate sources has been used (Aas et al, 2019; Ytrestøyl et al, 2015)

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