7315

• UCREFRP Catalog Number: 7315
• Author: Colorado Water Conservation Board.
• Title: State of Colorado Hatchery Feasibility Study for Endangered Fishes of the Colorado River Basin, Vols. 1 & 2.
• USFW Year: 1993.
• USFW - Doc Type: \
• Copyright Material: NO

. REFERENCE NUMBER:
CITATION:

008

Muth. R. T., T.P. Nesler, and AF. Wasowicz. 1988. Marking
cyprinid larvae with tetracycline. American FJSheries Society
Symposium. 89 - 95.

SPECIES AND LIFE STAGE:

CS, CS_LAR

TOPICS:

Research, Life History

KEYWORDS:

COLORADO SQUA WFISH, PROTOLARV AE, LARVAE,
'IEIRACYCLINE, OTOLlTIi, MARKING, PRESERVATIVES, TL

SUMMARY:

Four day old Colorado squawtish protoJarvae were exposed to different concentrations of
tetracycline hydrochloride over di1Jering lengths of time in an attempt to identify effective
marking tecJmiques. FJSh were held in 200 flowing well water troughs and fed live ArtemiJl Spa
nauplii and Tetra Min Fry Diet twice daily. Photoperiod was adjusted to 9-h light:15-h dark
at an intensity of 100 Ix. At the beginning of this investigation larvae were in swim-up stage
and had 50 - 70% of their yolk saa remaining. Total lengths were between 7.5 and 8.0 mm.

.

Exposure times for the different concentrations were 4, 12, and 36 h. Concentration levels
were 200, 350, or 500 mg tetracycline hydrochloride (TC) per liter aerated distilled water.
Distilled water was used as the diluent since TC binds to calcium. The pH for each test
solution was adjusted from 3.6 to 6.8-7.0 with tris buffer. Dead larvae were collected after each
treatment and survival rates were calculated. Ten living larvae were sacrificed from each
treatment group immediately after exposure and at weekly intervals after thaL Two
preservation fluids (95% ethanol and 3% formalin) were used to ew1uate their effects on mark
retention.

Colorado squawfish monality at durations of 36 h was high (71-100%) for all concentration
levels of TC. Exposures of this duration are not recommended. Monalities in the 500 mg TC
solution at 4 h were 16% and at 12 h, 24%. Monalities were minimal in lower concentration
of TC. Exposure to TC had no obvious effects on fish development or behavior. Pale yellow
external fluorescence was visible for 15 days following any TC exposure. This was most evident
in the yolk and gut regions. Fish preserved in ethanol showed this fluorescence more on the
dorsoanterior tip of the preopercal bone (not apparent in formalin preserved samples).
Otoliths of fish preserved in formalin either disintegrated during storage or were thin
transparent crumbly disks unsuitable for microscopic examination. Otoliths from fish preserved
in ethanol retained fluorescent yellow bands throughout the 77 days of the study. Overall mark
intensity was higher for the 350 and 500 mg/1 treatments and increased in intensity with
exposure time in all concenttations. The optimal survival and mark intensity is achieved by
immersing larvae in 350 mg TCIL for 4 - 12 hours. Samples should be preserved in 95%
ethanol with pH 8.0 even though some body desiccation occurs. Mark intensity did not seem
to decline after exposure to white lighL It is assumed that these marks may remain detectable
for several years ( 5-6 years in Kokanee in Lake Granby).

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