John, Their are lots of examples out there, but here are two papers describing experiments that are very similar to yours in many elements of design and execution, both involving fish, experimental streams, and comparisons that involve initial and final measurements on groups of individuals that are not individually identified.
Resetarits, W. J., Jr. 1995. Limiting similarity and the intensity of competitive effects on the mottled sculpin, Cottus bairdi, in experimental stream communities. Oecologia 104:31-38. Resetarits, W. J., Jr. 1997. Interspecific competition and qualitative competitive asymmetry between two benthic stream fish. Oikos 78:429-439. Good luck, Bill On 5/31/12 10:57 AM, "John Winkowski" <[email protected]> wrote: Hello fellow ecolog'ers, I am an MSc student studying environmental effects on phenotypic development and fitness of juvenile Atlantic salmon. I conducted a study where I incubated salmon eggs in 2 different environments, measured a few phenotypic traits, and placed equal numbers of fish from both incubation environments in "semi- natural" stream channels to measure survival and growth in the first 45 days post-emergence. Thus, fish from both treatment groups were competing in the stream channels with only natural prey items available. The fish were too small to individually mark them at the onset of the experiment, so I could only mark them to treatment with VIE tags. I was wondering if anyone had any suggestions on how to analyze such group data. Is it legitimate to compare average initial weight with average final weight? I have the lengths and weights at the onset of the experiment and at the end of the experiment. 40 fish from each treatment group went into each stream (thus, 80 fish/stream, with 8 replicate streams) and the streams were closed systems. At the end of the experiment I drained each stream and measured (length and weight) the surviving fish. Any insight would be excellent! Thanks so much. Cheers, John Winkowski
