Table 4.

The optimal dietary lysine levels based on different indices for grown-up grass carp (Ctenopharyngodon idella).

Item	Regressive equation	R2	P-value	Optimal dietary lysine level, g/kg
PWG	Y = −1.495 X2 + 40.618X −36.922	0.931	<0.05	13.58
Skin lesion morbidity	Y = 0.215X2 - 5.81X + 47.947	0.888	<0.05	13.51
Head kidney lysozyme activity	Y = −1.435X2 + 40.7X −80.103	0.936	<0.01	14.18
Spleen lysozyme activity	Y = −0.849X2 + 24.717X - 4.611	0.899	<0.01	14.56