Table 3 Arguments raised against the GOLT: Issues regarding gill surface areas.

NoArgumentsRefutations
3.1It was asserted (42) that “in morphometric studies
where both total lamellae area and gill mass
have been measured, a linear scaling
relationship (scaling exponent of 1.0) has been
found in fishes (43) as well as bivalves (44).
Consequently, there is no geometric constraint
that prevents an increase in body size (mass or
volume) from being accompanied by a
corresponding increase in gill mass and hence
respiratory surface area. In other words, gill
surface area can scale proportionally with body
mass and, if it does not do so, it is because
oxygen demands are reduced with body size.”
Several meta-analyses of gill surface area, covering
hundreds of fish species exist; they report
scaling exponents ranging overwhelmingly
from 0.7 to 0.9 (27, 58) and mention the
difficulties in obtaining accurate values when a
small range of body sizes are included (156).
Thus, the value of 1.04 mentioned here is not
representative of fish in general and a likely
overestimate, due to the largest specimen
considered being only 12% of the maximum
weight reported in L. unicolor (see
www.fishbase.org). The scaling exponent between
gill surface area and bivalve body weight
appears to range from 0.51 to 0.80 (58, 157),
with 0.85 in S. velum (44). The scaling exponent
of 1.0 linking gill surface area to gill mass in
S. velum is irrelevant to the O2 supply to its
body. Also note that the last sentence of the
argument precludes falsification.
3.2The presence of very large fish in warm tropical
waters, e.g., Goliath groupers (Epinephelus
itajara and Epinephelus quinquefasciatus),
sunfishes (Mola mola), billfishes and other
scombroids, giant manta ray (Manta birostris),
and especially the largest extant fish, the whale
shark (Rhincodon typus), refutes the GOLT,
which postulates that high temperatures tend
to reduce the size of fish (42). [This issue was a
genuine challenge to the GOLT, and its
successful resolution (see adjacent column and
main text) widened its scope.]
Following an extensive review of the biology of
the species in question (16), it concluded that
rather than being invalidated by large fishes
occurring in the tropics, the GOLT can be used
to classify their response to the challenge that
high temperatures pose to their metabolism.
Thus, in addition to breathing air, as often
occurs in tropical freshwater fishes, three types
of increasingly complex adaptations occur,
none mutually exclusive: (i) placid behavior,
combined with ambush predation (e.g.,
groupers) or filter-feeding (e.g., whale shark); (ii)
yo-yo–type swimming between the warm
surface and colder, deeper water layers and
feeding mainly near the surface (bluefin tuna
and whale shark) or at depth (swordfish and
billfish), the latter cases involving heating
systems to keep their huge eyes and brain
warm; and (iii) huge anatomical changes from
the ancestral fusiform shape, turning the body
into a shell around a cavernous mouth and
oversized gills (giant manta ray) or a mass of
inert jelly surrounding specialized locomotory
muscles (M. mola).
3.3Squid respire through their skin; moreover, by
having tubular bodies, squid have such large
respiratory area that they cannot be O2-limited
(158). In addition, their changed shape as they
grow increases the surface area of their body
hyperallometrically.
Squid do not breathe though their skin (159), and
even if they did, it would not matter because
their body surface (even when multiplied by 2
because of their tubular nature and even after
changing from roundish to lanceolate in the
course of their ontogeny) is much smaller than
that of their gill surface area.
3.4The demonstrably asymptotic growth of Growing
Sealife plastic squids implies that asymptotic
growth does not require a limiting surface (160).
A detailed analysis of what occurs in plastic squids
that “grow” when placed in water shows that,
actually (and surprisingly), it is a surface that
limits their growth (16, 33).