Identifier

etd-07032007-122846

Degree

Master of Science (MS)

Department

Oceanography and Coastal Sciences

Document Type

Thesis

Abstract

Developing organism-based metrics for assessing habitat quality is an important tool in conservation and restoration of aquatic habitats. The use of the RNA:DNA ratio as an early indicator of habitat effects on growth of nekton species has been suggested, but requires species-specific laboratory assessment prior to field application. We used food availability in laboratory treatments to simulate differences in habitat quality. Wild Gobiosoma bosc eggs were collected using nest-traps constructed of PVC pipe. Eggs from several different nests collected in the field were hatched in the lab, yielding larvae that were randomly assigned to three feeding treatments in two replicate tanks per treatment. Larvae were fed rotifers, Brachionus plicatilis, at densities of 20, 200, or 1200 l-1, in two trials lasting 10 and 8 days. Prey concentrations were measured every 8 hours and adjusted to nominal prey densities. One to five individuals from each tank, totaling 699 larvae, were sampled daily for nucleic acids. Wild larvae were collected using a light trap, and individuals were sampled identically to laboratory-reared fish to allow direct comparisons of growth and nucleic acid concentrations. Experimental fish exhibited significantly higher growth and lower mortality with increasing prey concentration. RNA:DNA ratios declined with age, length, and dry weight (DW) in all treatments. Wild larvae exhibited similar trends in nucleic acid accumulation as laboratory-reared fish. Ratios were lower in fish from higher prey concentrations when related to age, but showed no differences when related to SL, and were higher at higher prey concentration when related to DW. RNA:DNA ratios did not accurately reflect growth rate magnitudes (G d-1), but trends in growth and RNA:DNA were positively correlated. DNA:DW ratios proved to be a more accurate index of nutritional condition. I hypothesize that inherent growth patterns in larval Gobiosoma bosc largely prevent RNA:DNA from accurately reflecting nutritional condition, which has broad implications for use of this index in the field.

Date

2007

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Donald M. Baltz

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