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Keeping Fish as Pets

Keeping an aquarium successfully has parallels to biosphere maintenance on a spaceship. We talk about the technical complexity of the systems of life support.

Erasmus Erasmus : I have included this topic, not because I think the average person needs advice on keeping Fish as Pets. I have included this topic because one day the human race must become an aggressively spacefaring species to survive.
Keeping Fish as pets gives you experience with “biosphere” maintenance. The maintenance of environments suitable to sustain and maintain life.

Kinkajou Kinkajou : After all, you would have to ask yourself why you would keep Fish as pets? What do you get out of it? It is a hard question to answer. Dogs and cats and even birds can be affectionate and can form an interactive relationship with a person. Fish at most can only give you recognition. For example, a friend had some goldfish in a pond. He fed them every day. What he discovered was that the goldfish would only come out and waive their fins at him - alone. When other people visited, the goldfish would hide under plants such as the lilies and other pond features. They trusted only the person they knew and no one else. They were able to recognise the person they knew and to differentiate this person from other people. They were able to hold these memories for quite some time.
Goo the Numbat Goo : Apparently facial / body recognition doesn’t really need a lot of brain power. The goldfish seemed to do it well.

Fish In Tank
Fish In Tank : Neons - popular but not the easiest to keep.

Kinkajou Kinkajou : Keeping Fish is a challenge. It also gives a person a pride of achievement – the ability to boast about how pretty the tank is, how clever they are, what they have achieved and what difficulties they have overcome. Keeping Fish as pets can also give you something to do and can keep you quite busy.
Goo the Numbat Goo : Overall, it does seem an odd hobby. You really do need to ask yourself why do you do it? Perhaps it is just the indomitable human spirit seeking new horizons to search and conquer. It seems the best explanation I can come up with.

Kinkajou Kinkajou : So, tell us about some of the technical issues you have experienced in trying to keep Fish as Pets. What difficulties have you overcome in trying to keep your fish alive? What you do when your fish keep on dying? How do you save them?
Erasmus Erasmus : The first and most basic issue in maintaining conditions able to sustain life is redundancy. Any system failure could potentially result in the death of your fish. If you have one heater in a fish tank maintaining the temperature, you will have a problem if the heater stops working. A second heater in such a circumstance could save you from a catastrophic death event.
Even worse to consider, is the consequences of an over functioning heater. This heater goes into hyperdrive and keeps raising the temperature in the tank. If you have a large heater in the tank and it malfunctions, you have a reasonable chance of cooking all the fish in the tank. So, the issue here becomes that two smaller heaters is better than one large heater.

Redundancy backup and safety issues are critical in maintaining a life-sustaining environment. Monitoring your fish tank environment is obviously critical as well. And the environment monitors need to be simple, easily recognisable and requiring a minimal time investment to maintain and operate.

Redundant Reliability
Redundant Reliability



Kinkajou Kinkajou : Key life issues:
Erasmus Erasmus : Maintaining the correct temperature. Tropical fish need a specific temperature range to survive and thrive. You may be able to get away with temporary temperature drops. However, any sustained temperature change is likely to be lethal to your fish.
Erasmus Erasmus : Maintain adequate oxygen levels. Plant life can assist you in maintaining higher oxygen levels in the daytime. However, at night time, the entire biomass of the tank uses oxygen in metabolism and generates carbon dioxide. In short, every night oxygen levels fall and carbon dioxide levels rise. By definition this will create a pH change as well.
Conclusion: Plant life needs to be adequate but not excessive.
Erasmus Erasmus : Under gravel recycling systems can generate a flush of low oxygen water contaminated with bacteria and ammonia saturating the tank. Some people operating the systems have the pumps running the system 24 hours a day. Alternatively, they should at minimum be turned on for at least a few minutes every half an hour, to minimise the build-up of low oxygen water or toxic water.

It becomes obvious there are a "range" of life supporting operating parameters for a tank.

Undergravel FilterUndergravel Filter
Erasmus Erasmus : Excess pump strength. Generally, a specific size of tank requires a pump of a specific power to enable adequate turnover of the water. But if the pump is very powerful, the suction can catch fish and pull them into its mechanism. The water jets of water exiting from the pump can also push fish and hurt them, if they catch the fish by accident. It is impossible for a fish to be 100% aware of risks, 100% of the time. So yes the fish do cope with the high flow most of the time. But over days or weeks, one fish here or one fish there gets caught, gets pushed, gets injured and dies. Shielding the pump input can minimise the chance of a fish being sucked into the pump mechanism.

And distributing the pump output is important as well. Some pumps can have their flow-rates turned down. This is an excellent concept – akin somewhat to the use of fan speed on air-conditioners. At lower flow-rates, lower amounts of energy or power are available to push water around. Hence - less energetic and less dangerous water. But it is possible to crank up the output by adjusting the fan speed.  So, you can choose economy or workload depending on circumstances and tank environment.

But as a safety issue - high energy needs to be buffered.



Erasmus Erasmus : Excess nitrogen. Nitrogenous waste as nitrites and nitrates is less toxic than nitrogenous waste as ammonia. There are bacteria which will convert ammonia to nitrites and nitrates. This is the basis of biological filtration systems. The filter balls are colonised with specific bacteria which are able to take the ammonia and oxidise this, creating energy for themselves. Remember you need to obtain cultures of these colonising bacteria to colonise your system. They do not appear by themselves. Setting up biological nitrogen cycles takes time for the bacteria to colonise the system. Often you need a small quantity of “animals / fish” in the tank to get the nitrogen cycle to start to work - as a cycle.

Erasmus Erasmus : Excess plants. Plants are great. They assist in buffering the tank environment. They assist in absorbing nitrates, nitrites, ammonia and other minerals in the tank water. Removing excess plants can therefore remove excess minerals/contaminants from the water that have become “fixed” (incorporated) in the plant life of the tank..

But it is possible to have too many plants. Plants use oxygen at night.

Some plants such as filamentous algae form meshes which are quite capable of trapping and killing fish which become entangled within them.

Plants can also act to remove or metabolise toxins within the water. Biological systems create biological waste molecules. Plants can absorb and process metabolites/ chemicals in the fish tank water. These need to be cycled or recycled in some fashion.

For humans, there are definitely indoor plants that are capable of removing toxins from the air.  Some species of plants are far more adept at removing airborne toxins and chemicals than others. An efficient biological system must by definition be capable of cycling/recycling ALL biological molecules/waste. If even a single type of molecule were to not be metabolised by bacteria or plants, it is capable of holding up to toxic levels.

Erasmus Erasmus : Feral snails. If the population of a single organism such as a snail increases exponentially, it threatens the balance of the system. The snails use resources which are then unavailable to other animals. If the snails die, their necrotic biomass will pollute the system. And hungry snails cavorting around the fish tank, can jump on fish and attack and eat them if the opportunity arises. All creatures on planet Earth sleep. While asleep, animals such as fish cannot protect themselves, and can be susceptible to attack by even slow-moving but silent opportunistic “predators”.
Erasmus Erasmus : pH. The acidity of the water in the fish tank is a critical factor. Minerals, salts, bicarbonate and even living creatures such as algae can all buffer the system. That is, they can reduce the capacity of pH to change in response to acid/alkali inputs into the system.
Considering this in spaceship terms, your colonists need clean water and a clean environment for safety and survival.

Erasmus Erasmus : Base of the fish tank. Generally, 2 to 4 cm of small smooth rounded gravel pebbles are preferred on the base of the tank. Larger rocks at the bottom of the tank (with spaces between rocks), can allow fish to get drawn into under gravel filters and can get fish trapped between rocks.

The larger rocks can also allow influx of stagnant contaminants from the under-gravel filter zone into lower levels of the tank. A fish caught in a pocket of stagnant water coming up out of an under-gravel filter, will suffocate and die.

In short, sharp rocks and large rocks are not preferred on the bottom of the fish tank except as occasional aesthetic decorations.

Snails and other creatures can find a home between the rocks and make them difficult to remove. In the event of you disturbing larger rocks at the bottom of the tank, creatures such as snails can be caught resulting in a mass extinction event – triggering water pollution.

Kinkajou Kinkajou : There really are a lot of technical issues that need to be solved to maintain a fish tank. I can imagine maintaining an atmosphere in a closed environment such as a spaceship would be much more complex – especially on long missions. Travelling to the closest star system would qualify as being a long mission – requiring years of maintenance of the spaceship’s Biosphere.
To travel in small spaceships for long distances may be possible, but the biological recycling systems would need to be incredibly efficient for any long journey.
Erasmus Erasmus : Sewage processing systems are based on oxidation of bacteria over rocks. One very basic sewerage system is to spray effluent over rocks in a circular tank repeatedly to allow bacteria to degrade other bacteria. You face “sewage recycling “issues in fish tanks as well. Undergravel filters and the rocks at the bottom of the tank create a similar sewage over rocks system - similar to existing sewerage treatment systems near human cities. 

Kinkajou Kinkajou : The problem for fish being that they need to live with the sewerage processing system polluting the water around them, even as it does its job.

Erasmus Erasmus : The bacteria and biomedia in a tank need to be selected to the extent that this is possible. Some bacteria such as Pseudomonas bacteria can be a direct threat to fish. Some worms can be parasitic.

Micro plankton is important in the biology of a tank – especially in feeding baby fish.

Not all lifeforms are favourable to the continued survival of your fish, (or to humans on a spaceship). If you’re able to control your environmental biome, this can considerably enhance your safety and fish safety / survival.
Erasmus Erasmus : Toxic molecular build-ups. Bacteria form the basis of system that recycles organic molecules. Some molecules in the human body have a very long half-life. That is the body has a limited ability to metabolise and destroy them. Often these molecules are excreted by glucuronide conjugation. This is a simple process whereby the toxic molecule is attached to a sugar molecule and then dumped from the body by the liver and kidneys.

The original molecule still exists. Imagine if your biome did not have the capacity to process organic molecules such as aflatoxin – one of the most carcinogenic chemicals known to man, (generally sourced from fungal contamination of peanuts). If this chemical, is not broken down, even microscopic quantities could have disastrous consequences for our spaceship crew and colonists.

Just conjugating this toxic molecule with some sugar and excreting it from the body is not good enough. It is a molecule that needs to be processed and destroyed / fully inactivated.

Kinkajou Kinkajou :Many molecules can of course be incinerated. But how do you concentrate them sufficiently to incinerate them?
Erasmus Erasmus : There are ways, but it is complicated. Biological recycling is much more flexible, cheap and able to deal with micro inputs to the system.


Erasmus Erasmus : Inadequate food and nutrition. If you’re feeding your fish from “one” food source, (or your spaceship colonists with an artificially produced foodstuffs), you run the risk of a deficiency of vitamins / minerals and of essential “unknown” organic molecules.

If you’ are feeding your fish, you should be using at least two different foodstuffs (i.e., not just flake food day and night).

If you’re feeding your human colonists, it is quite likely we do not understand the consequences of the inadequate provision of many of the organic chemicals present in foodstuffs. For example, many of the green vegetables such as cabbages contain organic molecules that activate cytokines and leukotrienes. But I think that even today we do not understand the consequences of a restricted supply of these types of chemicals.

It is almost impossible to eat a limited diet on planet Earth. But in a spaceship, with limited variety and limited production of foodstuffs, it is an all too possible long-term scenario.

Erasmus Erasmus : Energy cost. The setup and maintenance of system requires energy to run it. Whether it is just electricity for pumps and filters in the fish tank or complex maintenance systems in the spaceship, you need to consider the maintenance cost of your systems. Yes it is possible to do many things. But in the long run we need to do as many things as possible - as efficiently as possible – to make the system sustainable.
Erasmus Erasmus : Shop and buy some spare parts. But in a spaceship with limited materials and the need for 100% recycling, you need to plan for the systems that can cycle/recycle and recreate new materials as industrial stock feeds. A spaceship may well need a supply of timber, metals, plastics, and silica related material such as glass.

New systems such as 3D printing may deliver a range of technical fabrication systems even to small ecosystems - such as space ships. But not everything can be fabricated in this fashion.

Filtration in Action
Filtration in Action

Erasmus Erasmus : Filtration. Filtration is necessary to purify the water, remove algae, and remove waists and contaminants or to accelerate the recycling of them naturally. Technology can create some amazing solutions.

In a fish tank, filtration can be done through fibreglass wool, ceramic or plastic biological substrates (as in bio filters), or charcoal systems. Reverse osmosis can remove solute and salts from a fish tank. A spaceship has a similar need to remove chemical particulates, smoke particulates, organic odour molecules, volatile organics, and even bacteria (Legionella is renowned for colonising showerheads. Older people breathing in shower mist can easily develop Legionella pneumonia).

Goo the Numbat Goo : So, we’ve gone through some of the factors which keep fish alive in a fish tank. In many ways these are relevant to keeping human beings alive in a spaceship. We need to take up the challenge of creating self-sustaining biomes with full recycling systems. If we are to go into space, bio- recycling becomes critical.