Cichlids by Sanderling

Nutrition and Waste Management

I started the road to becoming an organic gardener a few years ago and now after five years of lawn care, planting trees and shrubs, and looking after my wife’s roses and woodland garden, without the use of pesticides , herbicides or fertilizers. I allow myself the luxury of feeling a little smug when I watch all  my neighbour’s efforts using the vast chemical arsenal that is available at the local big box store and getting no better results for their efforts.

For lawns, the typical pattern of behaviour in my neighborhood is to apply weed killer and fertilise in early spring and as soon as the warm weather starts, begin cutting the grass every couple of days. I say ‘begin’ because for some folks it never ends. So begins the endless cycle; feed, water, cut, bagged clippings to the curb. If it looks like rain, some folks will apply more fertiliser and with any luck the grass will start growing even faster and thicker. Sound familiar?

In organic gardening the emphasis is on growing a lawn thick and tall with deep roots so that you don’t have to water it. I feed my lawn composted manure and cracked corn in the spring and thats it for fertiliser until the fall. I neverremove the clippings.  The neighbour on my left cuts his grass three times a week in the summer and waters his lawn every  morning. I cut my lawn three times a month and never water it and from across the street, you can’t see any differance in quality between the two.

Now at this point I should state that my aproach is as much out of wanting to minimse the amount of work and inputs that go into keeping my lawn at a standard that won’t irritate the neighbourhood as it is out of wanting to protect Mother Earth. I’m not lazy, just more interested in other things…

One Sunday morning while looking out my front window, enjoying a cup of coffee before starting my fish-room chores I watched as my neighbour began cutting his morning lawn maintenance ritual. It seemed that he had cut it only the day before yesterday and I found myself wondering why he was content to run on the lawn care treadmill expending so much effort, fertiliser, and gas for his lawnmower into cutting the grass. Was it to avoid the wife and kids?

Taking a sip of coffee I suddenly had a flash of self deprecating brilliance. I realized that I was on a similar hamster wheel in my fish-room- feeding my fish, changing water and feeding the fish again.

The more I fed my fish the faster they grew (or so I thought) and the more water I had to change. The more water I changed the healthier and more active the fish, and the more they ate. The more they ate the greater the frequency of water changes. In my fry growing system, I was doing 30 % water changes every  day. This amounted to nearly a 1000  gallons a week! It was time to take a hard look at the whole process and ask the question, “Am I feeding my fish too much?”

If you think you might be overfeeding then chances are you probably are.

In  aquariums the primary sources of waste if we exclude plant decay are fish excreta and uneaten food. The best conversion of feed to fish biomass obtainable in aquariums is approximately 30% for mosst of the fast growing species. That is to say that not more than 30% of the nitrogen and phospherous in fish food that is eaten is converted to fish biomass. The rest is excreted in both solid and soluble form.

Feeding frequency and activity has a significant effect on the health and quality of aquarium water. Changes in the amount of Biological Oxygen Demand (BOD), pH, concentration of chemical preservatives, suspended solids, ammonia, inorganic nitrogen, and phosphorous are all measurable as food is added to the system. Overfeeding contributes to the eutrophication of aquarium water, which may manifest itself with blooms of noxious algae. As closed systems the only relief is a water change. More feeding simply equates to more water changes.

It is the intent of this article to offer some guidance in feeding and filtration practice to the aquarist to manage the most efficient use of resources and limit the amount of time spent cleaning aquariums. In reducing the frequency and volume of water changes,  we lower the amount of stress on the fish and increase the time  available to enjoy the hobby in other ways.

 The chart above approximates a mass balance when we feed a medium quality fish food. By weight the food is 30 % organic nitrogen and 32% organic phosphorous  on average. Ash weighs in at around 8%. Higher quality foods boast lower ash content and have significantly less phosphorous due to the manufacturing process which removes bones (the largest source of phosphorous in food) fromfish that are used to make fish meal, which is a major ingredient in commercially available fish feed.

As stated earlier, 30% of the organic nitrogen and phosphorous is metabolised by the fish and the balance is excreted as waste. Aproximately 61 % of the nitrogen consummed in the food is excreted through the gills and kidneys as ammonia and urea. Details on how this takes place is beyond the scope of this article but more information can be found here. The 30% metabolisation rate is an upper limit, could be significantly less, and will vary by species.

Commercial food producers make their products to suit the nutritional needs of a variety of fish and concequently have to increase the percentage of proteins and other nitrogen bearing components in order to satisfy the most demanding of species. As a result there is often excess nutrient added to the food beyond what the fish can metabolize and this is destined to become waste.