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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43
such, asterisci are good indicators of minimum larval age. In Ad libitum larvae they are
readily visible under a low-powered dissecting scope at first appearance. Those from
Starved larvae were small and difficult to discern, indicating few energy resources remain

available to devote to otolith production after 14 d.

Increment formation begins at hatching. A "yolk check" was evident in many

otoliths at the time larvae shifted from endogenous (yolk) to exogenous feeding 6 to 7 d

after hatching. Increment formation proceeds at slightly fewer than one a day, with

lowest rates in Starved larvae (Tables 3-4).

This does not preclude age analyses, as increment formation need not necessarily

be daily but instead only follow a consistent pattern to be useful (Rice et al. 1985).

Reported rates for other taxa often fall less than one increment per day, even when daily

deposition occurs. As variability increases and age-ranges used decreases, the slope of

the least-squares regression will also decrease. I used a narrower range of age in the

Starved treatment than at other feeding levels, possibly explaining some differences.

Another factor lies in the ability to detect increments, which are more likely missed than

added in the counting process (Rice et al. 1985). It is apparent that otolith growth in

Starved larvae began to slow after about 12 d, which must represent a point at which

energy reserves are depleted and may also contribute to an apparently reduced number of

increment relative to age because of the decrease in increment spacing.

Increments were more difficult to discern and count in lower-food treatments be-

cause of decreased distances between them when otolith growth was reduced. Further, as

otoliths thicken, reduced resolution near the center may also result in lower counts