Time: Feed > Metabolize > Waste

[Trouser Bark]

For longer than I'll attempt to recall I've been giving my fish a high value meal 30-45 min prior to a WC. By high value I mean something like a Peacock Bass or an Arowana eating a Tilapia filet. I assume them to be a little like my dog in that I can feed my Dobermann breakfast and within a few short minutes he'll have extracted maximum value and be ready to toss the rest of it out in the yard as his morning constitutional.

I'm not sure how long it takes a fish to metabolize a meal though and I wonder if those 45 minute waits have been time wasted.

Am I the only one that does this?

What I'm looking for here is a poop expert. Somebody who really knows their sh*t.

I know you're out there.

Talk to me.

 

[wednesday13]

For longer than I'll attempt to recall I've been giving my fish a high value meal 30-45 min prior to a WC. By high value I mean something like a Peacock Bass or an Arowana eating a Tilapia filet. I assume them to be a little like my dog in that I can feed my Dobermann breakfast and within a few short minutes he'll have extracted maximum value and be ready to toss the rest of it out in the yard as his morning constitutional.

I'm not sure how long it takes a fish to metabolize a meal though and I wonder if those 45 minute waits have been time wasted.

Am I the only one that does this?

What I'm looking for here is a poop expert. Somebody who really knows their sh*t.

I know you're out there.

Talk to me.

IMO its not always the same as with a dog… or having a morning coffee … larger preds consuming large meals are going to digest over a longer period of time. Personally i only feed once a week very heavily. It takes a good 2-3 days for my fish to pass anything. Once a week is plenty for a large pred. Higher temps will speed metabolism but id still wager its not going to be the same day even. Your fish may be different if their already full when ur feeding them tho.

 

[jjohnwm]

The morning poopstitutional your dog produces right after breakfast...just like the one you do...is not composed of the stuff he (or you...) just ate. It's yesterday's meal, just being pushed down the conveyor belt to the exit hatch by the new stuff entering at the other end...or perhaps even older than that.

Back when I kept and bred large constrictors, they were fed mostly rodents but also periodically received newly-hatched chicks which could be gotten for free from a local hatchery (they only kept the females, while males were disposed of). Trust me when I tell you that a snake's "chicken turds" are completely unique and instantly recognizable...even before you see 'em. Same with monitor lizards; when they have been eating birds...you know it. Invariably, the animals would poop right after eating, but that was a normal garden-variety rodent turd; the chicken turd would not be seen until at least several days later, or even after the next meal which might be a week down the road.

For sure, you have occasionally seen your dog vomit up his breakfast, and that can happen hours after eating it. That means that it's still in the stomach at that point, hasn't even begun its long trek through the intestine. Use yourself as another example; when you eat corn at suppertime, the absolute earliest you will see it again is next morning, and more likely the next day, more than 24 hours after ingestion.

I give my Jelly Cat one or maybe two "high-value" feasts per month, interspersed with smaller meals. I do the big meals at least a day or two before regularly-scheduled water changes. And, frankly, I bet both of us are overthinking this; probably makes zero difference overall. A properly-maintained tank that gets big regular changes of water will be healthy regardless of when we feed...and one that doesn't get water changes and proper maintenance will be an unhealthy environment regardless also.

 

[Flaring Afro]

Not all animals have slow digestive systems. Many birds will have vegetation pass through in less than an hour. Dogs also are faster and more straight through than humans, though I believe it is true that it isn't the last meal passing in 30 minutes. Pigs are much closer to human digestion than dogs, I hear.

I have no idea how quick fish digestive systems generally are, so I can't help OP too much but I do doubt it is within 30 minutes. The idea of timing water changes with feeding schedule is intriguing though. This strategy could save time and money.

 

[Trouser Bark]

I bet both of us are overthinking this; probably makes zero difference overall.

You are no doubt 100% right but it's pretty tough to turn curiosity off. I believe I'll have a can of corn for breakfast and get to the bottom of this.

Or not.

 

[Milingu]

The question here is, what is your main goal with changing the water? Do you want to actively remove the feces or is the main goal to reduce nitrates and possibly their precursors?

If it is predominantly the latter, be aware that most of the ammonia is “exhaled” through the gills. This happens relatively continuously as long as the fish's metabolism remains at the same level.
Feces make up a smaller proportion here.

 

[duanes]

It appears that vegetarian cichlid species, have much longer digestive tracts, than carnivorous, in order to make best use of the less nutritious plants, they need to constantly graze on, compared to the high quality in meaty foods a P-bass might get.
But even in comparison, its not like the 30 feet we humans have, or the <15 ft in a dogs intestines
Below an X-ray of Cindelichthys pearsei,, a primarily vegetarian cichlid.

This may be why grazers like the above Cincelichthys, Tropheus or ithe Indian cichlid Etroplus (video below) need to constantly graze, to remain healthy, while a predator like Cichla or Gobiomororus can survive on 1 meal per week.

https://youtu.be/SPgRGQi0r1A

 

[jjohnwm]

The question here is, what is your main goal with changing the water? Do you want to actively remove the feces or is the main goal to reduce nitrates and possibly their precursors?

If it is predominantly the latter, be aware that most of the ammonia is “exhaled” through the gills. This happens relatively continuously as long as the fish's metabolism remains at the same level.
Feces make up a smaller proportion here.

Thanks, that is interesting info. I had always been aware that the gills were the main avenue by which ammonia left the fish's body, but without really thinking about it I had assumed that the speed at which ammonia was produced would be variable, and directly proportional to food intake and digestion.

But even if it isn't, the production of poops and also their size and volume are definitely related to food intake, and my shallow thinking wants the water to be both ammonia-free and also visibly clear. My casual observations seemed to indicate that the best time to grab fresh new turds, before they have a chance to break down and enter the "vicious nitrogen cycle", was a couple days after the big meal.

It appears that vegetarian cichlid species, have much longer digestive tracts, than carnivorous, in order to make best use of the less nutritious plants, they need to constantly graze on, compared to the high quality in meaty foods a P-bass might get.
But even in comparison, its not like the 30 feet we humans have, or the <15 ft in a dogs intestines
Below an X-ray of Cindelichthys pearsei,, a primarily vegetarian cichlid.

This may be why grazers like the above Cincelichthys, Tropheus or ithe Indian cichlid Etroplus (video below) need to constantly graze, to remain healthy, while a predator like Cichla or Gobiomororus can survive on 1 meal per week.

Also interesting data; it makes me wonder if there are any fish whose intestines can vary in length at different times of year, similar to those of some bird species, to allow them to better utilize seasonal food supplies.

But...it has always seemed to me that carnivorous fish took quite awhile to work their food all the way through their alimentary canal, despite having short intestines. With herbivores, it's tough to tell how long it's taking to pass through, since their food intake is constant and consistent, and their poops pretty much all look the same. So I'm not at all convinced that the length of the intestine is the only, or even the main, factor in determining how long it takes for a given bite of food to get from the piehole to the tarhole.

You are no doubt 100% right but it's pretty tough to turn curiosity off. I believe I'll have a can of corn for breakfast and get to the bottom of this.

Or not.

If there's one thing I like better than a good ol' DIY experiment...it's one that someone else does so I don't have to. Bravo!

Just in case one of the Usual Suspects makes their Usual Demand....I am going to get in front of that and ask for...no pics, please!

 

[RD.]

Also interesting data; it makes me wonder if there are any fish whose intestines can vary in length at different times of year, similar to those of some bird species, to allow them to better utilize seasonal food supplies.

Yes, absolutely. I’ve posted about this a number of times over the years, with regards to some of the various cichlids found in the Rift Lakes. Ditto to some of those same species when kept in captivity, and fed more nutrient dense foods. Their intestines decrease as they no longer require the same length to get the same job done.

 

[duanes]

Another interesting part of fishes food processing system, are its 2nd set of jaws.
Beside the obvious jaws we can see, on the carnivores below.
Most fish have another set of Pharyngeal jaws in the throat

Carnivores 2nd set in the throat are long and can be thrust forward to help further capture and hold multiple prey, secure those prey items in time of a food glut, then move ithem down the tract for further processing.

That 2nd set of pharyngeal jaws of vegetarians are spaced differently, and shaped more for grinding gritty algae and other plant fibers.

Although I have been a vacuumer for aesthetic reasons in the past, these days I seldom bother with turds, because "lower" animals like shrimp and snails in my tanks substrate and sumps tend to break them down quickly, and the ammonia from the gills, and other chemical waste that accumulates most often on the waters surface, where it inhibits gas exchange.
This is why during a power outage, we get white or oily slick on the air water interface, and why surface skimming and fractionation are more efficient ways of ridding a tank of pollution, than sucking up turds

And these "lower" animals break down stuff, to easily become food for plants.

I realize some here might get bored because I sometimes go on "ad nausium" about the importance of planted sump/refugiums as the major factor in efficient filtration, but I give 2 sh**s about turds, that in the end, feed my sumps overabundance of plants.