Three Ways To Grow Fish... Or Not

Floating Islands Help Fish Grow and Prevent Algae from Growing

A nice stringer of bass caught in BioHaven-enhanced Fish Fry Lake

​Of the nearly 10,000 BioHaven floating islands launched since Floating Island International opened its doors in 2005, a sizable number have been focused on fishery enhancement.  People like myself, who grew up with a fishing pole in their hands, pick up on the idea that nature can be helped.  Nature can be enhanced.  Building an ultimate fishing hole, or supporting a public fishery with good habitat design, has motivated many island launches.  But there’s usually only a vague understanding of just how floating islands help fish grow.  For certain, the other two popular methods to grow fish are better understood.  But are they better for water?

​Through much of the U.S., especially in the southern and central states, fish are fed commercial fish food.  Folks are taught how to condition their fish and orient them around feeder technology and product. The fish pellets look like rabbit food. They spray out on a regular basis, and specific varieties of fish can be conditioned to the feed. Eventually the fish will be there, and the water may boil with aggressive feeding as the shower of fish pellets occur.  

This approach is also employed by fish farmers too. It’s how aquaculture operates.  Fish are contained within ponds, or nets in marine settings, and fed their pellet ration.  Conditioning the fish to compete and consume as much as possible is the ongoing goal in such settings.  And the pellets include both, organic protein and mineral nutrients, in what a fisheries expert will describe as an optimal diet.  

The method works, and remarkably heavy, fat fish are farmed this way.  It’s aquaculture, fish farming, and it’s a proven way to grow fish.  But this system adds nutrients to the waterway, in the form of the “balanced” nutrient and mineral content of the pellets, and it’s always a bit uncertain as to the threshold…just how much of the fish pellets to add before the water becomes too nutrient rich.

The second approach is more focused on nature’s model.  It’s approaching one of nature’s methods, at least.  

In this setting, a waterway is spiked with fertilizer.  Owners or managers strew pellets of fertilizer across the water.  The plan is that the fertilizer will grow beneficial green algae.  Not blue-green, or cyanobacteria, but green algae, which in turn grows zooplankton and such, and triggers the food web.  This approach has been described and expanded on in great detail (for example, in Bob Lusk’s Pond Boss magazine) and is a favorite for southern water.  Water managers are actually taught to target a certain level of water turbidity, as it defines a rich phytoplankton bloom.  They are taught by fisheries specialists that there’s a balance, and they can achieve it by measuring and tracking a range of factors like dissolved oxygen, BOD, and such.  Their intent is to trigger one of the two primary engines of life…sunlight driven plant growth.  Phytoplankton to zooplankton and on up the food web.  This fertilization process is the second most frequent method to grow fish.

Fisheries specialists warn that it’s possible to over fertilize.  The result can be dramatic swings in dissolved oxygen levels, and fish can be killed, suffocated, if the balance is skewed. Note the old southern proverb… you're not a fish farmer ’till you’ve had a fish kill!  It’s important to note that adding fertilizer and trying to steer it towards a specific form of phytoplankton is edgy, at best.  Here in the north, few fishery managers go this route.  Those that do normally hedge their bets and provide aeration systems to guard against the suffocation risk.  And it’s revealing to note that when water does use up its oxygen, instead of simply generating carbon dioxide anaerobic bacteria take over, and they produce methane.  Methane, after correction for time in the atmosphere, is some 25 times more impactful than CO2.

I remember fishing on Richmond Mills with my wife Anne, when – after fishing all day without a catch - she finally hooked and landed a three-pound bluegill.  Frustrated, she’d craftily embedded her hook into a fish pellet, and thrown it into the maelstrom of boiling water as a fish feeder on the reservoir was strewing fish pellets into the gullets of ravenous fish.  I’ll tell you what…a three-pound bluegill is exciting!  Richmond Mills used option #1 to grow fish, but the reservoir enjoys another tactic as well.  The reservoir, which is an incredible fishery, contains dozens of naturally-occurring floating islands.  The combination of fish feed, the fish farm approach, and the floating island factor results in a tremendous fishery.

Fish using roots under a BioHaven as security cover and a food source

What if Richmond Mills also fertilized their water, and added aeration too?  Then they could have the first fish growing factor, fish pellet feeding, and the second factor, phytoplankton bloom, both occurring in tandem.  And they already have the naturally-occurring floating islands.  Is it possible that, at least in the Richmond Mills setting, three systems by which to grow fish could happen concurrently?

There are two primary engines of life: autotrophs get their energy from sunlight and heterotrophs get it from eating other living things. The chicken, or the egg.  You can grow phytoplankton, as in plants, by adding minerals and nutrients, which is what approaches one and two can achieve.  Or you can grow zooplankton directly, by providing a living food source…as in organic biofilm.  The best part of this third way (to grow fish) is that it comes with far less risk than either of the other two forms. One doesn’t add fish pellets or fertilizer to a waterway.  Instead, one adds surface area and circulation.  These are the two primary variables for supporting heterotrophic life… as in zooplankton and invertebrates, and on and on up the food web.  

This story is really about nature’s ladder of life.  We can circumvent it and feed fish pellets, and hope for the best.  It’s a proven method, but the result is a farmed fish.  For some reason, it’s just not quite the same as “wild”.  

Or we can spike our water with fertilizer, minerals, and hope that we get it right, and don’t ultimately inspire a bloom of the wrong kind of phytoplankton.

Or we can provide surface area and circulation, which is what floating islands do.  We can target heterotrophic life forms, instead of autotrophic ones.  The potential here is vast.  And you get a bonus with choosing option 3: it is not as exposed to dissolved oxygen deficit as either method #1 or #2.  The reason?  It’s because all water includes diatoms, a form of phytoplankton that occurs in low light settings.  These guys move through the same cycle as other forms of phytoplankton but do so on a much more extended basis.  It takes weeks for a bloom of diatoms to cycle through a system, instead of “hours” in the case of cyanobacteria.

Diatoms are always a component of the third system.  They will be in the mix, in the periphyton that results when surface area and circulation take place in low light conditions, like under and within floating islands.

So my question is this: What will happen when all three of these fish growing strategies come together? Are we talking new World Record fish?   

A new Montana state record largemouth bass was recently harvested from a eutrophic waterway in the same watershed that our research lake, Fish Fry Lake, is located in.  And while I restrict Fish Fry Lake to option three, I’m tempted to incorporate #1 and #2 as well.  Tempted!  

This summer will be my decision marker.  Here we are in the midst of climate change… warm winters, cool springs, hot summers and extended warmth through the fall.  Ideal conditions for harmful algae bloom, but so be it.  I will track what goes on here on Fish Fry this summer, and I will try to be objective.  

Can hardly wait!