At first, this seems like a no-brainer; if you add nutrients, you
grow phytoplankton, which are food for fish. But growing fish in
aquaculture is actually done a very different way. Carp, which is
the major food fish grown by aquaculture in the world today, are
produced by adding nitrogen and phosphorus to small ponds where
carp is the only fish present and not surprisingly carp grows quite
well. Catfish is another bottom feeding fish that is produced successfully
through aquaculture, and also grows well under these conditions.
But what would happen if you added inorganic nutrients to real
lakes with complex food webs? Would fish yields increase? The answer
is that the success is somewhat mixed and limited, especially for
target fish species. Sometimes you get fish, but you don't necessarily
get the ones you wanted.
had to look really hard to find these two studies that demonstrate
that increase nutrient additions to lakes leads to increase fish
production. Here is the application of fertilizer by seaplane to
some very oligotrophic (i.e. low nutrient, low biomass) lakes in
British Columbia. This is work by John Stockner and colleagues and
the probably the closest study we have to oceanographic analogy,
because these are really oligotrophic lakes.
scientists fertilized quite a few lakes, and here are a few variables
before and after fertilization, and the percent change. So after
fertilization, we've double the chlorophyll concentration, which
is a measure of phytoplankton growth. That is a pretty impressive
result. We also saw a big increase in zooplankton, which is essentially
the food for small fish. There was a measurable increase in younger
fish, and one-year-old salmonoids, but we had no data on adult fish.
So can we increase fish production in British Columbia lakes by
adding nutrients? Maybe is how I would characterize that work. At
least we can increase the production of young fish. It was not evident
that you could increase the production of adult fish.