MEPS 412:231-245 (2010)  -  doi:10.3354/meps08686

Using Gambusia affinis growth and condition to assess estuarine habitat quality: a comparison of indices

Bryan P. Piazza1,3,*, Megan K. La Peyre2

1School of Renewable Natural Resources, Louisiana State University Agricultural Center, Baton Rouge, Louisiana 70803, USA
2US Geological Survey, Louisiana Fish and Wildlife Cooperative Research Unit, School of Renewable Natural Resources, Louisiana State University Agricultural Center, Baton Rouge, Louisiana 70803, USA
3Present address: The Nature Conservancy, PO Box 4125, Baton Rouge, Louisiana 70821, USA

ABSTRACT: Numerous indices have been used to estimate fish growth and condition; however, differences in sensitivity and reliability of the methods have hampered efforts to identify appropriate indicators for routine evaluation of habitat quality in the field. We compared common morphometric (length, weight, somatic growth, length-weight condition) and biochemical (RNA:DNA ratio, relative DNA content, energy density) growth indices on the same wild-caught mosquitofish Gambusia affinis to examine their usefulness as indicators of habitat quality. A laboratory experiment was used to quantify growth rates of wild-caught G. affinis under different feeding treatments. Field studies consisted of both a short-term enclosure experiment (10 d) and weekly (7 wk) fish collections to compare growth indices in managed inflow and reference marshes during a winter/spring freshwater pulse event in upper Breton Sound, Louisiana, USA. Marshes flooded by restored freshwater pulses were capable of producing optimum growth (0.001 g DW d–1; DW = dry weight) and energetically valuable habitat (>6000 cal g–1 DW) for trophic transport. Because of differences in timing of response, morphometric and biochemical indices were generally not directly correlated, but there was clear agreement in direction and magnitude of response. The most striking difference in timing was that biochemical indices (RNA:DNA) responded more slowly to treatments than did morphometric growth indices. While gross patterns are comparable between indicators, differences in sensitivity and response time between indicators suggest that choice of indicator needs to be accounted for in interpretation and analysis of effects.


KEY WORDS: Growth · Energy density · RNA:DNA ratio · Resident species · Poeciliidae · Estuary · Fish · Louisiana


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Cite this article as: Piazza BP, La Peyre MK (2010) Using Gambusia affinis growth and condition to assess estuarine habitat quality: a comparison of indices. Mar Ecol Prog Ser 412:231-245

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