Substituting fishmeal with lupin Lupinus angustifolius kernel meal in the diets of cobia Rachycentron canadum: Effects on growth performance, nutrient utilization, haemato-physiological response, and intestinal health

Abstract

The purpose of the study was to investigate the impacts of dietary narrow-leafed lupin Lupinus angustifolius kernel meal (LKM) on growth performance, feed utilization, digestibility, haematology, as well as liver and intestinal health of juvenile cobia Rachycentron canadum. Five isonitrogenous (crude protein around 460.0 g/kg) diets were formulated to replace 0, 200, 400, 600 and 800 g/kg of fishmeal protein with the protein from LKM designated as LKM0, LKM20, LKM40, LKM60 and LKM80, respectively. Triplicate groups of cobia were fed the respective diets for a period of 56 days. At the end of the feeding trial, growth indices expressed as final body weight (FBW) and specific growth rate (SGR) decreased following the linear and quadratic models with increasing levels of LKM. Feed intake, protein retention and energy retention followed the same trend, whereas, feed conversion ratio (FCR) and hepatosomatic index (HSI) followed a reverse trend with FBW and SGR. A significant decrease in the apparent digestibility coefficient of protein, lipid and dry matter was observed in cobia when more than 400 g/kg protein from fishmeal was substituted by LKM protein. Haematological indices such as red blood cell and haemoglobin declined significantly in fish fed with LKM60 and LKM80, while a significant increase was observed in aspartate transaminase and alanine aminotransferase. Histopathological alterations including higher lipid deposition, necrosis and vacuolization were found in the liver of fish fed higher (>600 g/kg) fishmeal protein replacement levels. Similarly, intestinal structure was affected by higher replacement level of fishmeal protein (>600 g/kg) as fold height and goblet cells decreased significantly with increasing levels of LKM. The results indicate that 200 g/kg fishmeal protein can be replaced by protein from LKM and substitution beyond that level adversely affected the growth performance of cobia.