Table 1 Sample calculations used for modeling eye and brain costs for a 4-g fish.

		Pachón	Micos	Surface	Data origin
a	Whole-body minimal metabolic rate (mg O₂ hour⁻¹ per 5-g fish)	0.8328*	0.929^†	1.026*	Published data
b	Whole-body oxygen demand (mg O₂ hour⁻¹)	0.686^‡	0.766^‡	0.846^‡	a(4 g ÷ 5 g)^0.862
c	Brain mass (g)	0.027	0.031	0.034	4 g × organ mass scaling relationships in table S2
d	Relative brain mass (% body weight)	0.68	0.78	0.85	c ÷ 4 g
e	Brain metabolic rate (mg O₂ hour⁻¹ g wet mass⁻¹)	1.603	1.603	1.603	Data from the current study
f	Brain oxygen demand (mg O₂ hour⁻¹)	0.043	0.050	0.055	e × c
g	Relative brain cost (% body O₂ demand)	6.27	6.52	6.50	f ÷ b
h	Eye mass (g)	0	0.038	0.090	4 g × organ mass scaling relationships in table S2
i	Relative eye mass (% body weight)	0	0.95	2.25	h ÷ 4 g
j	Eye metabolic rate (mg O₂ hour⁻¹ g wet mass⁻¹)	0	0.525	0.525	Data from the current study
k	Eye oxygen demand (mg O₂ hour⁻¹)	0	0.020	0.047	j × h
l	Relative eye cost (% body O₂ demand)	0	2.61	5.56	k ÷ b
m	Neural tissue (eyes plus brain) oxygen demand (mg O₂ hour⁻¹)	0.043	0.070	0.102	f + k
n	Neural tissue cost (% body O₂ demand)	6.27	9.14	12.06	m ÷ b
o	Cost of vision (% body O₂ demand)	0	3.52	6.97	(m_Micos − m_Pachón) ÷ b_Micos
					(m_surface − m_Pachón) ÷ b_surface

*Data taken from Moran et al. (19).

†Estimated as a rate equidistant between Pachón and surface ecotypes based on data from Hüppop (11).

‡Mass metabolism scaling exponent (0.862) taken from Moran et al. (19).