Scale size in balistids is not well quantified in the literature.
Therefore, we made a survey of the size of the scales from the
side of the body (i.e., excluding the sometimes larger and more
elongate scales at the rear of the abdomen associated with the
expansible dewlap) from specimens in the collections of the
National Museum of Natural History. Examination of 21
species of balistin triggerfishes (the more generalized of the
two groups of balistids), representing nearly all of the genera,
shows that the greatest dimension of the scales is usually
between 2%-3% (range l%-4%) SL, but as much as 5% SL in
Pseudobalistes flavomarginatus (Riippell) and 7% SL in
Odonus niger (Riippell). The thick scales in the aberrant
Xenobalistes (enlarged coracoid, postcleithra, and frontal),
which has some superficial ostraciid characteristics, are about
3.3% SL (Matsuura, 1981:194). The scales in the Oligocene
genera Balistomorphus and Oligobalistes are only impressions
that are difficult to measure, but from their pattern they
obviously were small and in the size range of 2%-3% SL like
those of most Recent balistins. The scales of monacanthin
filefishes tend to be slightly smaller and thinner than those of
balistins, and to bear upright spinules, while in some
specialized species the scales are almost entirely lost. Thus, the
scales in balistids are small, except in a few derived genera of
balistins with scales of moderate size, even though the basal
scale plate may be thicker in balistins than in triacanthoids.
Among the Tetraodontoidea, the monotypic Eocene Zignoichthys
(Zignoichthyidae) has small scales (0.9% SL) with
upright spinules very similar to those of the Triacanthodidae,
the most generalized family of the order, while the monotypic
Eocene Eoplectus (Eoplectidae) has moderately enlarged scales
(5.8% SL) with stellate radiations from the base of a central
upright spinule. In the Triodontidae, another relatively generalized
family of tetraodontoids, the scales are relatively small
(3% SL) except where more elongate in the expansible dewlap
of the abdomen. Elsewhere in the Tetraodontoidea the scales
often are enlarged as either fixed or erectable spines in most
Tetraodontidae and Diodontidae, except where the spines are
secondarily reduced or lost in some tetraodontids. However,
enlarged plate-like scales similar to those of ostraciids are
found in the tetraodontid Ephippion and in the molid Ranzania.
The scale plates of Ephippion are up to 9.2% SL in large adults
and form a firmly sutured girdle around the middle of the body
(more extensively so than in Eospinus, although the latter has
a girdle at a much smaller body size than does Ephippion).