Marine ash‐products influence growth and feed utilization when Atlantic cod Gadus morhua L. are fed plant‐based diets

Atlantic cod Gadus morhua L. were fed high plant protein diets added to either shrimp-shell meal or crab-shell meal. The aims were to investigate if diluting dietary energy would reduce the liver index (HSI) and if marine ash would add value to plant protein-based diets. Two control diets were used: a high plant protein control diet (PP) with no marine ash addition, and a fishmeal-based diet (FM) with no marine ash addition. All diets were evaluated in small cod (initial weight 79 +/- 15g) and in market-size cod (initial weight 1579 +/- 20g). Addition of crab-shell meal up to 20% and shrimp-shell meal up to 10% did not influence liver size in either small or market-size cod. An addition of up to 20% crab-shell meal and 10% shrimp-shell meal improved growth compared to the PP control diet, and stimulated increased feed intake. However, 10% shrimp-shell meal and 20% crab-shell meal diets resulted in a similar intake of energy and protein as the control groups. Increasing shrimp-shell meal to 20% resulted in reductions in feed intake, fat digestibility and growth, and in altered gut histology. All diets, except the 20% shrimp added diet, resulted in normal ranges of plasma nutrients and blood hematological values, showing good fish health with or without the marine ash addition.