Freshwater Pipefish

If I haven’t said this explicitly yet, pipefish are typically saltwater fishes. We knew of the populations in Alabama, which I’ve already written about, and had heard rumors of Florida populations. One thing we’re interested in is local adaptation, which we can address using freshwater colonizations by saltwater fish.

So while we were in the Jacksonville area (where we went after our collections in Perry), we decided to check out the St. Johns River. We ended up driving much further south than the outlet of the river to the ocean, but we found the eelgrass that our fish love so much and found a decent population! The next day we decided to try another site further south, and again found fish! Finally we decided to try Lake George, which is likely the furthest away from saltwater the fish would probably go in this river system. After gaining access to the eelgrass in the lake by some incredibly helpful and friendly homeowners, we found a third population! It was really exciting. We’re hoping to discover how isolated the freshwater populations are from each other and from saltwater populations using population genomics approaches. Here’s a map of where we collected the freshwater fish (the yellow pins). The closest saltwater source would be the Atlantic ocean up near Jacksonville, and the pipefish would have had to swim upriver.

Another interesting thing about the freshwater populations is that they all had odd sex ratios–we found very few adult males, and even fewer that were actually pregnant. There were plenty of females and lots of juveniles. These unusual ratios could be explained by several things:

1. Maybe the adult males tend to be in deeper waters than in which we were collecting (this would be surprising, as saltwater males are usually found in shallower grass beds than the females).

2. There could be some physiological tolls that exist for males but not for females as a result of living in frehwater instead of saltwater.

3. There may be more pollution, in either amount or concentration, in the freshwater lakes and rivers than in the saltwater ocean. Pollutants like endocrine disruptors could alter sex ratios by feminizing males and biasing the development of the offspring.

We’re pretty excited about the possibilities that these collections present!

To put a damper on our excitement, we failed to find any viable seagrass beds anywhere near Jacksonville or St. Augustine, meaning that our closest saltwater populations to the freshwater fish are in Titusville.

We do now have three sites in Titusville, and tomorrow may be adding yet another–this one near a power plant! Today was a good day, in which we collected fish from two different sites near Cape Canaveral, saw a baby alligator at a very high salinity site (that was also really mucky), and saw a couple dolphins and a couple manatees.


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