8142

• UCREFRP Catalog Number: 8142
• Author: Horn, M. J.
• Title: Nutritional Limitation of Recruitment in the Razorback Sucker ‎(
• USFW Year: 1996.
• Copyright Material: NO

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40

and examined directly with transmitted light at 160 to 1000 X. The structures are small

and transparent enough that grinding or polishing was unnecessary. Longer focal lengths

at lower magnifications typically provided better resolution through curved otolith

surfaces; higher magnification was required to resolve questions of increment separation.

Clearing through penetration of immersion oil increased contrast within a few minutes

and enhanced analysis for a number of hoW'S. Increments, defined by contrasting light

and dark regions, were counted at least twice for each otolith. Otoliths "over-cleared" in

immersion oil within a day, with increments becoming difficult to count as the medium

and otolith became more similar in light refraction. A plastic mounting medium suffered

the same drawback and was deemed unusable.

Sagittae, at least for younger larvae, proved most usable because of their rapid

increase in size. Lapilli counts were only made when questions of increment clarity

resUlted in problems. For unknown reasons, accurate numbers of increments could not be

ascertained in 10 to 15% of all otoliths examined.

Time of first increment formation was estimated by least-squares regression of

total increments with known age of larvae in days as the dependent variable. The Y-axis

intercept was the time of first increment deposition. Rate of increment formation was the

slope of the regression; a slope significantly different from 1.0 indicated other than daily

formation.

Determination of increment deposition based on growth rate was done by com-

parison of slopes and intercepts of regressions through use of analysis of covariance

(ANCOV A) across the three feeding treatments. The ANCOV A interaction term was