Waste production-fish vs corals

[drainbamage101]

So had this discussion a lot with my roomate (yes we argue/talk about reef related things very often) and besides using armchair science, can't come to any sort of conclusion about this.

lets take a clownfish and a chalice

Into the clownfish, i insert 5 grams of food (in a manner where he spits none out, none escapes gill, etc, clown receives 5 grams of food.)
Clown now excretes 2.5 grams of waste, having consumed the other portion via energy needs.
2.5 grams worth of waste is then processed through the nitrogen cycle and helps in the creation of a degree of phosphates, etc.

take a chalice, give it 5 grams of food (same as for fish)
Chalice now excretes X grams of waste, which then goes on to react in Y way with water column, in respect to the clownfish's waste


What's X and Y, and why?

 

[JHemdal]

Interesting question, I think that biologists would answer it in the opposite direction - they would place the animal in a respirommeter and measure the oxygen uptake. From that, everything else can be extrapolated. This has been done with both corals and fish (but I don't have the studies handy).

Because of the zooxanthellae in the chalice coral, the numbers would be skewed. If you chose a non-photosynthetic coral, you would still need to ensure that the biomass was equal between the coral and the fish.

Also, it would depend if the clownfish is actively growing or not - if you feed a non-actively growing fish too much food, a higher percentage of that food is excreted undigested.

Ultimately, I think you're asking is there a difference between food energy conversion rates between corals and fish - IDK for sure, but there probably is - there are even differences in food conversion rates between species of fish.


Jay

 

[drainbamage101]

Thanks for the reply Jay,

And yea, I know the variables are off the wall, which makes it tricky to come to any sort of consensus with any precision, the main reason I'm curious is for the far less scientific question:

If I feed 1 cube of frozen food to corals in a tank with no fish, do I require the equivalent level of filtration if I had fed 1 cube of frozen food to fish in a tank with no corals consuming the food.

And of course that impacts water changes and what not, hence the curiosity.

 

[iamwrasseman]

i would also tend to think that the clownfish consumes energy way beyond that of a chalice as a result of physical activity that is expelled through swimming .

 

[drainbamage101]

i would also tend to think that the clownfish consumes energy way beyond that of a chalice as a result of physical activity that is expelled through swimming .

Thus the clownfish would actually excrete less waste in regards to this, right? That's where our armchair science has gotten our argument as well, but somehow our coral only tanks require less maitenance, even though there's actually greater amounts of food put into the coral only tanks

 

[greenbean36191]

Well there are 3 things to consider. First is that 5 grams of food goes a whole lot further for a coral than for a fish. The metabolic rate for a coral or anemone ranges anywhere from about 3.5-16 times less than a clownfish. Also, some (in some cases, a lot) of the nitrogenous waste produced by corals is assimilated by the zooxanthellae rather than excreted into the water. Finally, the amount of N assimilated in tissue vs excreted is going to depend a lot on the growth phase of either animal and how quickly they're growing or producing gametes.

So imagine in your scenario that you have a chalice with exactly the same biomass as a small clownfish (that's a big chalice since we're not including skeletal weight). If that fish ate 5g of food over the course of the week, it would take the chalice over 5 weeks to eat the same amount of food. So even if we assume they have the same food conversion ratio and the same percentage of their food gets excreted as DIN, realistically the coral is really only producing about 1/5th of the N per unit of time as the fish, even before you consider the portion taken up by the zoox.

The zoox complicate things further because the rate they uptake N is highly dependent on whether N is limiting or not. When N is abundant, the zoox take it up at a lower rate than when N is scarce. If your water is very low in nitrogen and the coral is fed infrequently, then the measured N excretion rate of the coral is going to be lower than if DIN is high or if the coral is fed frequently.

Last, young fish tend to have a higher feed conversion ratio than older fish whose growth has slowed. That means that as fish get older and their growth slows, for every g of food fed to them, more and more of the N in the food gets excreted as waste rather than turned into tissue. Size tends to have much less effect on corals and anemones which generally don't have asymptotic growth.

The real answer to your question is going to be highly dependent on the FCR of the fish and on the N starvation of the zoox in the coral. The practical answer though is that corals excrete far less N than fish per unit of time simply because they consume less per unit of mass.

 

[drainbamage101]

Well there are 3 things to consider. First is that 5 grams of food goes a whole lot further for a coral than for a fish. The metabolic rate for a coral or anemone ranges anywhere from about 3.5-16 times less than a clownfish. Also, some (in some cases, a lot) of the nitrogenous waste produced by corals is assimilated by the zooxanthellae rather than excreted into the water. Finally, the amount of N assimilated in tissue vs excreted is going to depend a lot on the growth phase of either animal and how quickly they're growing or producing gametes.

So imagine in your scenario that you have a chalice with exactly the same biomass as a small clownfish (that's a big chalice since we're not including skeletal weight). If that fish ate 5g of food over the course of the week, it would take the chalice over 5 weeks to eat the same amount of food. So even if we assume they have the same food conversion ratio and the same percentage of their food gets excreted as DIN, realistically the coral is really only producing about 1/5th of the N per unit of time as the fish, even before you consider the portion taken up by the zoox.

The zoox complicate things further because the rate they uptake N is highly dependent on whether N is limiting or not. When N is abundant, the zoox take it up at a lower rate than when N is scarce. If your water is very low in nitrogen and the coral is fed infrequently, then the measured N excretion rate of the coral is going to be lower than if DIN is high or if the coral is fed frequently.

Last, young fish tend to have a higher feed conversion ratio than older fish whose growth has slowed. That means that as fish get older and their growth slows, for every g of food fed to them, more and more of the N in the food gets excreted as waste rather than turned into tissue. Size tends to have much less effect on corals and anemones which generally don't have asymptotic growth.

The real answer to your question is going to be highly dependent on the FCR of the fish and on the N starvation of the zoox in the coral. The practical answer though is that corals excrete far less N than fish per unit of time simply because they consume less per unit of mass.

Very good write up, thanks!