Thumbrule to stocking?

[shrimpkeeper222]

guys I think I need you guys to help me deciede on one important thing-what is a thumbrule to perfect stocking??? I have heard it many ways;
1. inch per gallon(us)
2. inch and a half per gallon(us)
3. 1 small fish per gallon
4. 1cm for 1 cubic cm
5. just cover enough shoaling space and foraging space for fish without the water parameters going crazy(well a good rule, but not precise)
So, what is ur idea? And also plese tell me if my tank is stocked alright!
volume-14.6(US gallon)-tall,
acicity-6.0,
water parameters-good enough to keep the shrimps blooming!
filter-sponge with 60l filtration skill
temp-22-26'C
feeding-courgette slice, hikari crab cuisine, hikari frozen bloodworms, Decapsulated Brine Shrimp Eggs
plants-lush vegetation(moss, pellia, java fern, bladderwort, various floating stem cuttings(all gifts from shops), anubias nana, marimo balls, water lily, and yes, more moss!!!)
space, layout-middle is a lump of moss and driftwood, but swimming spaces surround the tank with open spaces-some patches of foraging grounds
stock-pygmy cories(7), otos(6), Neocardina.sp(hybrids, yellows, cherries, wild type) colony-number is 100+. Small number of copepods, daphnia, planaria, nematodes and ostracods breeding.
Is this an overstock??? Or is there some space to increase pygmy cory shoal?

[dw1305]

Hi all,
I'd leave your stocking where it is. You may find you need to reduce the number of Planaria, but your

Corydoras

should spawn successfully and with nothing to eat the eggs, or fry, that will add more numbers.

Could you could harvest a few of your shrimps? If you thinned them out you could add a few more

Corydoras pygmaeus

, but I still wouldn't go over 10.

think I need you guys to help me deciede on one important thing-what is a thumbrule to perfect stocking??? I have heard it many ways;
1. inch per gallon(us)
2. inch and a half per gallon(us)
3. 1 small fish per gallon
4. 1cm for 1 cubic cm

You can't really use linear measurements for fish length to give you a rule.

The problem is that volume increases as a cube of length. Ten one centimetre fish produce much less bioload than one ten centimetre fish does. Assuming that morphology doesn't change (and this is a hypothetical cuboid fish) 10 x 1 cm fish have a total volume of 10cm3, and one 10 cm fish has a volume of 1000cm3.

This is the length weight relationship for more normally shaped fish (and I would suspect that most Catfish have similar values)



<https://en.wikipedia.org/wiki/Standard_weight_in_fish>

There is also oxygen requirements to factor in, large fish have proportionally larger oxygen demand than smaller fish, partially because the gill area increases as a square (10^2) whilst body volume increases as a cube (10^3).

cheers Darrel

[Jools]

Now that is fascinating. One day I will model this...

Jools

[Bas Pels]

There is also oxygen requirements to factor in, large fish have proportionally larger oxygen demand than smaller fish, partially because the gill area increases as a square (10^2) whilst body volume increases as a cube (10^3).

When I was a student (long ago) I did consider going into fish agriculture. In fact I did get a reader, and surprisingly, this reader tolt me basically the oppositie was true. The oxygen demand decreases when a fish grows. The weight of the fish to the power 0,85 usually fits the data best.

That is, 1000 fish of 1 gram need more oxygen than 1 fish of 1000 gramms. This was explained by referring to hart reate - small animals have a higher hart rate than large ones do, and thus a higher metabolism.

[bekateen]

Oh, I have so much to say here and no time to type... Later today.

[bekateen]

Although there is a little bit of comparing-apples-to-oranges occurring here, @Bas Pels is correct.

Sa and vol.jpg (24.07 KiB) Viewed 4249 times

As shown above, in animals that grow geometrically (I.e., as a proportional increase in body size, which some animals do and others don't), body volume (V) increases in proportion to length (L) cubed (L^3) and surface area (SA) increases in proportion to length squared (L^2). And since body mass is proportional to body volume (assuming tissue density doesn't change with body size), then body mass is proportional to L^3... I believe it is from this latter point that @dw1305 gets his graph. So where is the discrepancy?

All of this material falls under the physiological subject area called "allometry," in which physiologists want to know how to model metabolic processes like whole body metabolic rate mathematically relative to body mass in order to (1) predict metabolic rates for newly discovered species, and (2) to be able to recognize when animals don't match these predictions, potentially revealing special physiological abilities.

Early on, two conflicting hypotheses developed:

1. Metabolic rate (MR) should be proportional to BODY MASS (M). If every gram of tissue uses the same amount of energy (and oxygen in aerobic species), then MR ∝ M. If this hypothesis is correct, then 100 fish, each 2 grams in size, eat the same amount of food as a single 200 gram fish, and likewise they all need the same amount of oxygen and produce the same amount of waste.
2. Metabolic rate should be proportional to RELATIVE SURFACE AREA. If metabolism is somehow limited by, or linked to, exchange processes occurring between the body and the environment (e.g., movement of heat, oxygen, carbon dioxide, etc.), and if these exchanges are occurring across body surfaces, then MR ∝ SA. IF SA ∝ L^2 and if volume ∝ L^3 and if volume is proportional to mass, then the RELATIVE surface area (surface area per unit volume) is proportional to M^2/3. If this hypothesis is correct, then larger animals need LESS energy per gram than smaller animals do; in other words, our 100 2-gram fish need more food, need more oxygen, and make more waste than our single 200 gram fish.

Summary, if metabolism (and oxygen use) is related to total mass, then MR ∝ M. (blue line in graph below)
If metabolism (and oxygen use) is related to relative surface area, then MR ∝ M^2/3 ∝ M^0.67. (gray line in graph below)

metab.jpg (30.61 KiB) Viewed 4249 times

When actually measured, real MR data is proportional to values ranging from M^0.75 to M^0.8 (what BasPels mentioned, and orange line in graph above). This is true across a broad spectrum of animals, from small insects to whales and elephants. Oddly, it applies to ectotherms and endotherms alike, even though their metabolic rates are very different. Scientists have tried to use a lot of different models to explain this. Some recent explanations apply principles from (a) mathematical fractals, (b) biomechanics and structural support limitations, and (c) "four-dimensional scaling." None fully explain this relationship.

The take-home message is that real gram-for-gram metabolic rates decrease as an animal's total body mass increases, so stocking rules based on mathematical linearity don't work. If MR ∝ M^0.75 or ∝ M^0.8, then a tank which can handle one 4" long fish cannot handle four 1" long fishes.

Cheers, Eric @bekateen

[shrimpkeeper222]

I didnt understand half the stuff that was said, but the reason I asked, is because I've been seeing less of my pygmies after i addded the otos. It is good to see that my tank stock isnt overstocked, but I thought it was beacause the tank was over stocked-apparently not-so why?

[bekateen]

Sorry about that, shrimpkeeper222. I went off on a tangent.

Unfortunately, I have no experience keeping either pygmies or shrimp, so I don't know what to tell you.

Sincerely, Eric

[dw1305]

Hi all,
Gentleman if you go from a comparison of length to a comparison of mass you are comparing "apples to oranges", because using mass you are then you are looking at metabolic rate against volume, and as you said larger organisms have lower metabolic rates.

But the question was about a length based stocking rule, not a weight based one.

I don't suggest any-one tries this, but if you progressively oxygen deplete a tank with fish of the same species, but different lengths, you will find the longest (most massive) fish will begin to show distress first, and if you continued this process, would die first. They have a much larger volume to surface area ratio due to their size.

It is because small fish can survive in more oxygen depleted water than adults, due to their high area to volume ratio, that fish fry can use thermal refuges, where warm water temperatures depletes the oxygen to levels that exclude larger fish.

cheers Darrel

[Bas Pels]

It is because small fish can survive in more oxygen depleted water than adults, due to their high area to volume ratio, that fish fry can use thermal refuges, where warm water temperatures depletes the oxygen to levels that exclude larger fish.

cheers Darrel

As the warm water areas are generally very shallow, other good reasons for the mature ones avoiiding them exist. Further, warm water may be good for fry (high temps mean high matabolism, that is rapid growth (assuming enough food)) but might be rather harmfull for adults - high metabolism means aging rapidly. Or unwanted growth.

I don't know of any research, but I could wel imagine the gill area in fry is either smaller or less used than in adults. Alfter all, if a gill branches when the fish matures, the gill area is used more efficiently.

[dw1305]

Hi all,
Unfortunately I don't know enough about fish physiology to know what changes occur during fish growth. It may be that large fish are more tolerant of lower oxygen levels, but that small fish can make use of the more highly oxygenated water at the gas exchange surface more easily.

I'm not at work at the moment, but I would imagine there must be research on Atlantic Salmon (Salmo salar) that looks at size class and resistance to hypoxia?

cheers Darrel

[bekateen]

Just to clarify, I wasn't thinking only of oxygen, but also of dietary food demand and metabolic waste production (particularly, ammonia release): the more food you put into the tank to maintain the fish, the more waste they will produce and the faster you'll pollute the water.

[dw1305]

Hi all,
I'll get the references when I'm back in work on Monday, but from what I could get the consensus is that large salmon are more tolerant of low oxygen levels than smaller fish in aquaculture systems, presumably for the reasons that "Bas Pel" posted earlier in the thread.

What I haven't been able to find yet is whether there is any work specifically on smaller containers (like aquariums).

cheers Darrel

[shrimpkeeper222]

Thanks for the input. I have reduced feeding and did a 25% WC, and the cories reemerged! Though it was a cool water change, they do not show much spawning behaviour.

[dw1305]

Hi all,
I've got an updated reference: Chabot, D., Steffensen, J. F. & Farrell, A. P. (2016). "The determination of standard metabolic rate in fishes". Journal of Fish Biology 88:1 pp. 81 - 121 (I can email a copy).

It isn't the easiest of reads, but I think the relevant bit for why larger fish (of the same species) are more prone to damage by low oxygen levels than smaller ones, in aquaria, than their lower metabolic rates would suggest is (from Chabot et al. 2016):

...with large fishes using more oxygen per unit time, but less oxygen per unit mass per unit time within a species....

It also has a bit on length mass relationships

Standard Metabolic Rate (SMR) is linearly related to body mass after logarithmic transformation of both variables .....but the relationship can differ for larval and post-larval states...... Therefore, comparisons of SMR should acknowledge the need to treat mass as a covariate or scale SMR for a standardized mass. This scaling is only possible for individuals of the same life stage but with different masses, as the scaling exponent may change for different life stages

I also found a paper by Jay Nelson (at Towson University) in the same Journal, Nelson, J. (2016) "Oxygen consumption rate v. rate of energy utilization of fishes: a comparison and brief history of the two measurements" Journal of Fish Biology 88:1 pp. 10 - 25. I don't know if he has done any new work specifically on Loricariids (see http://www.planetcatfish.com/forum/view ... hp?t=32382).

The take-home message is that real gram-for-gram metabolic rates decrease as an animal's total body mass increases, so stocking rules based on mathematical linearity don't work. If MR ∝ M^0.75 or ∝ M^0.8, then a tank which can handle one 4" long fish cannot handle four 1" long fishes.

It can, we are still at "apples and oranges", the metabolic rate is mass based (^3), but then you've used it here on a length basis (^1).

You will have less bioload with the four smaller fish, because the mass of the four 1" long fish will be considerably less than the mass of the one 4" fish.

If you use the Burbot formula Ws = 10-4.868 L2.898 , (because they are elongated fish like many catfish), and 1" is equal to 25.4mm (and 4" ~ 101mm), and multiplying the result for the single 4" fish by the 0.75 MR, you still find that the larger fish has added almost twice the bioload when compared to the 4 smaller fish, formula from:



cheers Darrel

[Shane]

Shrimpkeeper,
The "fatal flaw" of the stocking guidlines you mention above is that they only account for 50% of the impact of keeping fish in an enclosed environment. The various mass and length guidelines only take into account "Garbage In." Just as important is "Garbage Out" which is a combination of frequency and volume of water changes, filter capability, media used, filter and media maintenance schedule, presence of plants, etc.

You can keep a healthy heavily stocked tank by upping Garbage Out in relation to Garbage In. However, if your lifestyle does not allow you to commit a lot of time to daily maintenance you will be happier with lower stocking levels.

I am travelling a lot right now and have low stocking levels so my wife only has to do 40% water changes once every 10 days. Once I am home I am sure new fishes will be added and I'll be back up to weekly 70% water changes to maintain the same water quality.
-Shane