7018

• UCREFRP Catalog Number: 7018
• Author: Muth, R. T. and T. P. Nesler
• Title: Marking Colorado Squawfish Embryos and Newly Hatched Larvae With Tetracycline
• USFW Year: 1989
• USFW - Doc Type: The Southwestern Naturalist
• Copyright Material: YES

434 The Southwestern Naturalist vol. 34, no. 3
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Fic. 1-Microphotographs of unground otoliths under white (left) and ultraviolet (right) light. A.
Sagitta from a 10.3-mm total length (TL) Colorado squawfish larva that was immersed as an embryo
in a 200-mg tetracycline hydrochloride (TC)/I solution for 24 h, about 15 days after hatching. B.
Sagitta from a 10.8-mm TL Colorado squawfish larva that was immersed immediately after hatching
in a 350-mg TC/1 solution for 12 h, about ] 5 days after hatching. Fluorescent mark indicated by m;
edge of otolith under ultraviolet light indicated with dashed line.

water bath at 20°C. Post-treatment procedures were the same as far larvae in the embryo-marking
experiment.
In the embryo-marking experiment, egg-hatching success and fish survival, growth (TL increment),
and development were similar for all experimental groups (including control). Percent egg hatch was
high and ranged from 95 to 100% of the total number of eggs per group. Fish survival during the first
3 days after treatment was over 95%. Highest mortality (16 to 42% of the total number of fish per
group) occurred on day 4 posthatching. Thereafter, survival was over 90%. Otoliths from all treatment
larvae examined by UV-light microscopy had distinct, lucid to bright, yellow fluorescent marks (Table
1, Fig. 1). Mark intensity was slightly higher for the 24- and 36-h treatments in both TC concentrations
throughout the 15-day experiment.
Survival, growth, and development of fish were similar for all experimental groups in the newly-
hatched-larva marking experiment. Fish survival was high during TC exposure and during the first
3 days after treatment, ranging from 97 to 100%. Highest mortality (17 to 40% of the total number of
fish per group) occurred on day 4 posthatching. Thereafter, survival was over 90%. Distinct, yellow
fluorescent marks were visible in otoliths of all TC-treated larvae examined by UV-light microscopy
(Table 1, Fig. 1). Overall, mark intensity was higher For the 350-mg/1 treatments and ranged from
lucid to bright. For the 200-mg/1 treatments, mark intensity increased with exposure time; marks were
faint to lucid for the 4-h treatment and lucid to bright for the 12-h treatment.