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When we closely observe the behaviour of our aquarium fishes we soon get used to their swimming patterns and posture, recognising different ‘personalities’ in fish, such as boldness or aggression towards tank mates. Any departure from this usual state of affairs is often the first sign that there is a problem, and a fish that starts twitching, shimmying, shaking, rubbing, flicking or flashing against objects in the tank can often be a sign of a potentially serious issue. Fish flick and scratch for the same reasons that other animals including humans, they are trying to relieve irritation and dislodge foreign objects from the skin. Different fishes will show many varieties of this behaviour. Open water shoaling fishes may frequently visit the substrate of the tank and very rapidly rub their flanks against the gravel or sand – blink and you will miss it. More sedentary bottom dwellers can be observed ‘rocking’ against items of hardscape in the tank. Erratic behaviour in fishes may not always indicate a problem with their fish. Interestingly many Corydoras catfishes can often be observed darting up to the water surface incredibly quickly before resuming their bottom-dwelling location. This isn’t another form of the flicking/flashing behaviour, in fact, Corydoras under these circumstances are taking little gulps of air down into their intestine where a highly vascularised portion of the gut is able to extract the oxygen from the air. Should your Corydoras be showing this behaviour then consider increasing the aeration in the tank, but there should be no need to worry that the fish’s skin is being damaged or irritated. The skin of a fish provides numerous important functions; it is a barrier against the external environment, sealing the internal mileu of the fish and preventing infection by pathogens. Most notably the skin contains the scales, which form a tough outer armour present on most aquarium and pond fishes. The skin is the site of protective mucous secretion amongst other immune factors, it houses receptors for touch, smell and even taste. We can separate the skin of fishes into two principal layers, an inner dermis which contains blood vessels, nerves and sensory receptors, scales and connective tissues. Beneath this layer lies the muscle and above lies the epidermis, (‘epi’ meaning ‘on top of’). The epidermal layer contains many layers of cells that are toughened with the protein keratin in many species. Also present are mucous producing goblet cells in the epidermis. There are two principle irritants to the skin, water-borne pollutants and pathogenic infections. Flicking, flashing and scratching behaviours could be caused by irritation of the skin by high ammonia levels in the water, extremes of pH or residual chlorine in the water due to ineffective or absent tapwater conditioning. Clearly thorough testing of the water is going to be essential, for many fishkeepers water testing is only undertaken when problems such as this arise. Tetra’s new water testing app, used in conjunction with Tetra’s 6in1 test strips will allow rapid and accurate determination of the water quality using your smartphone, and provide recommendations on how to treat the water, such as adding Tetra EasyBalance to reduce the number of water changes and stabilise important water values. Any ammonia in the water is likely to be detrimental to the fish and causing skin irritation amongst many other deleterious symptoms. Admittedly, the toxicity of ammonia is pH dependent, however, it is best to regard ammonia as toxic, full stop! Obviously different fishes are adapted to varying pH ranges and this must be taken into account before considering if the pH value is extreme for the fish. In addition, the historical pH values will be important, if there is a rapid, sudden and large change in the pH this can cause considerable skin irritation to the fish whereas a slow onset change within the same values may be adapted to. When any fish are flicking and scratching in an aquarium the first action to take is a thorough appraisal of the water quality, this can hopefully be viewed in the context of historical readings. If water quality is the source of the problem then this will obviously need to be corrected. Ammonia levels can be high in new aquaria that have not been properly matured, in overstocked or overfed tanks and can commonly occur in tanks following a significant power cut. If the pH value is found to be substantially lower than the fish would prefer, then it is important to check the carbonate hardness (KH), also. Carbonate hardness is able to buffer the water against pH change, hence by monitoring and maintaining KH we can prevent sudden and severe plummets in the acidity of the tankwater. If the pH is found to be extremely high, then the most likely explanation is that some new calciferous rockwork has been added to the tank, this will have leached alkaline minerals into the water forcing the pH substantially upwards. It might be the case that this water quality analysis fails to turn up any obvious suspect parameter, perhaps a more sinister water parameter is to blame such as copper, or more likely the fish are infected with ectoparasites. There are numerous organisms that can thrive on the skin of stressed fishes, some graze the mucous or epidermal cells, others burrow deeper to the dermal layer whilst large ectoparasites like the fish leech or the fish louse are seeking the fish’s nutritious blood supply. Effective diagnosis is the key, addition of an antiparasitic agent to treat flicking / flashing fish, when the real cause was ammonia poisoning or an extreme of pH, would be catastrophic, hence water quality problems must be ruled out first. Ironically many ectoparasites only infect fishes already pre-stressed by some other factor – most likely poor water quality! If water quality can be truly ruled out, the type of parasite causing the problem must be determined so the best treatment can be selected. Some ectoparasites are large enough to see with the naked eye, other

Before considering why we should ensure our fishes are fed whilst we are away from our aquarium or pond during the holidays it is worth reminding ourselves why we feed fish in the first place! The diet of any animal contains proteins, fats, carbohydrates, vitamins and minerals as these are required for the production of new tissue as the animal grows and repairs or recycles transient tissues such as blood cells. These nutrients are also used as energy sources to power muscle movement, nervous communication and numerous other physiological and biochemical processes. Different animals require variable amounts of these nutrients. For a community of fishes in the average tropical aquarium, goldfish tank or pond, fats and proteins are of prime importance as an energy source. These typical ornamental species have a gastrointestinal tract that is different from ours in one important respect – the majority of common ornamental fishes lack a stomach so are unable to store large infrequent meals. In the wild, many of our aquarium and pond occupants’ ancestors would have been constantly foraging and feeding on low nutritional value items which is why there was no need for a distensible-walled stomach. In addition, the lack of high protein in the diet means efficient protein digestion in an acidic environment is unnecessary. This is in comparison to carnivorous fish which eat infrequent, large, protein-rich meals and therefore require a distensible-walled, acid-containing stomach to store and efficiently digest their meal. When it comes to our typical community aquarium, goldfish aquarium or garden pond we are looking to feed our fish small regular amounts of food – as much as the fish will eat in 2-3 minutes 2-3 times per day. If we can feed less, with a greater frequency, even better as this caters for the constant foraging behaviour and the steady trickle of food through the gut. This is fine when we are around our tanks daily, feeding perhaps morning, afternoon and evening, however we do not want to be slaves to our aquaria or pond – us fishkeepers need a break too! One of the biggest concerns we hear at Tetra when talking with prospective new fishkeepers is “how do I feed the fish when I go on holiday?”. Imagine we have a matured tropical community aquarium with all the usual suspects within –various tetras, angelfish, corydoras and we have two glorious weeks in a sunny climate booked. Passport ready, suitcase packed, taxi booked – what options are open to us for feeding the fish while we are away? Let us consider the first option, to do nothing. Fish can survive periods with no food in the wild surely? The impacts of fasting on a range of fishes has been studied, but the effects are far from clear. Studies in carp (Cyrprinus carpio), show the short-term response to fasting involves mobilisation of fat reserves for energy primarily in the first phase which can be up to eight days. If fasting continues then the fish starts to raid its own protein stores for energy leading to muscle wasting. Many fishes are able to adapt to a lack of food in their environment and decrease their metabolism accordingly. However, this fasting usually accompanies some environmental cue such as a drop in temperature. Studies in salmon have shown that during winter fasting there are marked changes in the length, thickness and surface area of the intestinal layer. A finding that was interestingly also found in the marine blue damselfish (Pomacentrus coelestis) when they were fasted for 13 days mimicking the time in transit in the ornamental supply chain. In these species this has consequences for digestive efficiency when the fasting period is over and feed should be offered at progressively increasing fractions of the pre-fasting feed rate. In tropical fishes it can be a rise in water temperature as seen in the dry season that is associated with the lack of food and enforced fasting. Hoplias malabaricus, an Amazonian carnivore characin can survive up to 180 days without food, interestingly the drought season of its habitat rarely lasts longer than this. Therefore, if there is an ability of the fish to adapt to fasting this will usually be accompanied by environmental cues warning the fish that a dearth of food is coming. We do not have control of these environmental cues in the aquarium and especially in the garden pond and so fasting the fish is not an option. Holiday Foods  Holiday foods are one option for feeding fish over the period. These contain small food items of a low nutrient value bound to a matrix. The low nutrient value is important as it is quite possible that the fish will not eat the holiday food as it is presented in a format markedly different to the normal diet and they can be wary of novel items in their environment. If the food is uneaten and contains the high protein levels seen in flake, pellet or crisp diets then a mass of food applied will cause a serious depletion in water quality. TetraMin Holiday food for instance has a protein concentration of 3% whereas the TetraMin flake protein level is 47%. The matrix used in some holiday feeder blocks can affect water chemistry in the tank as they dissolve and so it’s important to test a holiday feeder block before the holiday to give the fish a chance to accustom to it, realise it is a safe food source and for the fishkeeper to be on hand should any problems arise. TetraMin Weekend is a great solution to this lasting up to six days. Another option is to get a friend or neighbour to feed the fish, if they are a fishkeeper also, then fine, they will know about things like not overfeeding and ensuring the filter is working. You would not want a novice fishkeeper making elemental mistakes on your tank! Perhaps if the helper has not looked after fish before, give them instructions to feed up to three every day, once

Little snacks between meals are very popular with humans and animals alike, and fish are no exception. Treats for aquarium inhabitants to snack on add variety to their daily menu and broaden their diet. Aquarists can also benefit from spoiling their creatures with treats every now and then. Tempting treats Fish snacks come in a wide variety of shapes, flavours and colours – from natural foods to adhesive tablets and even gel foods. Despite all of these differences, they have one thing in common: they add variety and make feeding even more fun. Face to face with fish Fish, crustaceans and other aquatic creatures are not the only ones who benefit from the snacks: by feeding their creatures treats such as adhesive tablets, aquarium owners also get the chance to see them from a different perspective. Watching the creatures so close to the glass is great fun, especially for children. What’s more, the fish chasing after their snacks can make extraordinary subjects for aquarists who enjoy taking photos of their finned friends. Special snacks sometimes even help to lure more timid creatures in front of the lens. By sticking a treat onto the aquarium glass to examine the fish more closely, you are more likely to be able to spot a sick fish at an earlier stage. Healthy treats for fish The same principle applies to treats as to any other food for aquarium creatures: it is important to avoid causing any problems or spreading any illnesses through feeding. When using frozen foods, for example, the cold chain must always be maintained, otherwise the food will spoil. Natural foods (e.g. live food that you have caught yourself or natural food that has not been adequately checked) may be contaminated with pathogens that are harmful to the creatures in your aquarium. If these pathogens end up in your aquarium, you may introduce a fish disease as a result. It goes without saying that natural, certified-quality foods should always be free from pesticides and heavy metals. All in all, it is crucial for your fish treats to be of impeccable quality, as this helps to keep all of the creatures in your aquarium healthy. Tetra treats – certified quality and processes Our treat product tips: ideal treats for your fish include the meticulously tested and checked Tetra adhesive food tablets, the Tetra FunTips Tablets, Delica natural food and Tetra FreshDelica germ-free gel food.

Mucous membrane and gill parasites Symptoms: Sometimes, aquarium fish can be infected with mucous membrane and gill parasites without you noticing anything. This is because minor infections tend to be without symptoms and most of the potential pathogens are microscopic. The symptoms only become apparent in severe cases and None are indicative of a specific parasite. They include a dull mucous membrane, rubbing against objects in the tank and heavy, unnatural breathing. Cause: The best known of these mucous membrane and gill parasites includeSingle-celled organisms such as Costia, Trichodina, Chilodonella as well as Ichthyophthirius and Oodinium (the latter two are described below). The multi-celled organisms include skin and gill worms of the Gyrodactylus and Dactylogyrus genera. Remedial action: You can find suitable medication in pet stores. Please remember that well-kept fish have a healthy immune system and can therefore often keep pathogens at bay by themselves. White spot disease Symptoms: Your fish have white, pinhead-sized dots on their skin and fins. Their mucous membrane may also be peeling off in places. They are rubbing against objects and breathing heavily. Please note that the white spots only develop in the course of the infection. You should also watch out for ‘Ichthyo’ (white spot) when the initial unspecific symptoms appear and start the treatment as quickly as possible. Cause: The symptoms are caused by a single-celled skin parasite called Ichthyophthirius, which is generally introduced when adding a new stock of fish. ‘Ichthyo’ infects virtually all freshwater and brackish fish, and can also escalate rapidly. Remedial action: Carry out a partial water change without delay and buy a suitable medicine from a specialist retailer immediately to treat the infection. Please make sure that you stick to the exact usage and treatment instructions specified on the product. In most cases, several consecutive treatment cycles are required. Fin rot & mouth decay Symptoms: The fins of infected fish look frayed and the edges of the fins may appear whitish. Many fish also have open wounds, especially at their fin base. The mucous membrane and eyes may look cloudy. In cases of mouth decay, fish often have a whitish, cotton wool-like covering and tissue damage on their mouth. Cause: These infections are caused by bacteria. However, they are often signs that something else is amiss because they predominantly target fish that have a weakened immune system, are infested with skin and gill parasites, are kept in poor conditions or are generally stressed. Remedial action: Apart from using a suitable medicine, it is vital to take measures to improve the environmental conditions, reduce stress and boost your fish’s health. These include carrying out a partial water change, cleaning the substrate, generally improving the water quality, providing a diet that improves the fish’s health and checking the fish stock (avoiding overstocking, taking social compatibility into account). Specialist retailers can provide effective medicines that must be used in line with their instructions. You should never use antibiotics unless prescribed by a vet. Fungal infections Symptoms: Cotton wool-like patches appear on the skin and fins. These often subsequently form around the edges of wounds or in inflamed areas. Cause: Fungal infections are triggered by fungal spores, e.g. of the Saprolegnia genus, which are always present in the water. They mainly affect fish with a weakened immune system or which are injured and have damaged mucous membranes. Remedial action: Fungal infections can be treated with suitable medicines from specialist retailers. However, you should always remember that these are secondary infections and therefore the main cause needs to be found and treated. This means that you need to improve the living conditions, e.g. the water quality, and that you should bear in mind that your fish may also have a parasitic or bacterial infection. You should also check your fish stock: check whether your fish get along together well and how they react to measures to boost their fitness (e.g. feeding). At the same time, you need to establish the cause of the problem. Are the water values correct? Is the temperature suitable for the species of fish? Could the fish be wounded? Fish tuberculosis Symptoms: The fish have sunken or bloated bellies. They may develop bulging eyes or bellies and parts of their fins may be shortened and frayed. They seem pale or their skin is inflamed. In many cases, their scales stick up or even fall off. The fish appear lethargic and isolate themselves. Take note: in the early stages of the disease, your fish may seem fighting it as the pathogens initially spread in the internal organs. Cause: Fish tuberculosis is caused by bacteria of the Mycobacterium genus. These bacteria are naturally present in the tank and mainly affect fish with a weakened immune system as well as stressed or old fish. Fish tuberculosis may progress slowly or very quickly or even lie latent, but it is always infectious. Remedial action: Fish tuberculosis itself cannot be treated with medicine, but you can certainly stop its progress. It is vital to improve the living conditions. Offer your fish the water values they need, carry out regular partial water changes and feed them only top-quality brand foods. Check the stocking density, for example. Please note that in extremely rare cases, mycobacteria may infect open wounds in humans, triggering a harmless, local and treatable skin inflammation and skin hardening. If you have a wound on your hands, you should always wear suitable gloves when putting your hands in the aquarium, for hygiene reasons. ‘Hole in the head disease’ Symptoms: Cavities start to develop, particularly on the head of the fish, small at first then increasingly bigger. In many cases, a whitish, pimple-like coating becomes apparent. Fish look as though the tissue around the head is eroding away. Cause: The exact cause of ‘hole in the head disease’ is far from clear, but a group of single-celled intestinal parasites, e.g. Hexamita, are thought to be at least partly responsible. Bacteria and potentially a lack of minerals or nutrients could also be the

Stress can affect our well-being, damage our health and cause diseases. This not only applies to humans but also to animals, including fish. But stress isn’t always a bad thing; in fact our well-being can even be increased when exposed to positive stress, known as “eustress”. For aquarium fish, a typical example of this is the feeding process. When we first appear in front of our aquarium to feed our fish, they often seem anxious and timid because the situation is unusual and stressful for them. Once feeding becomes a routine, they adapt to the “stress” and start to perceive it positively because they look forward to eating their food.   While a certain amount of stress can have a positive effect on the fishes’ organisms, continuous stress can put a serious strain on the creatures. If fish are exposed to stress over a lengthy period, this can weaken their immune system and cause “adaptation diseases”. As a result of chronic stress (or “distress”), the adaptation phase ultimately enters a tiredness phase because the stress inducers won’t go away and the organism cannot recover. At some point, the fish end up exhausting their energy reserves and their health deteriorates.   What are stress factors for fish?   Stress is caused by various excessive strains and/or stress factors which can be very different in nature. What’s more, each fish species responds differently to a certain strain. For example, a specific stress factor may trigger a high level of stress for one fish species, but have a very mild reaction for another species. Such strains mostly occur when fish are kept in unfavourable living conditions.   Combining fish species   One of the potential causes of stress is when fish are kept with incompatible species in an aquarium. A high level of stress arises, for example, when fish that are in a predator-prey relationship are kept together despite being incompatible due to their opposite ways of living. Keeping rival species together also puts a strain on fish. Since they have to share the same habitat, they evolve into predators that compete for food and space, stressing each other out.   Moreover, it is not advisable to keep very active fish together with species requiring peace and quiet. The active fish will expose the quiet fish to constant stress, causing them to withdraw and seek hiding places. A further stress factor is an overstocked aquarium, i.e. when there are too many fish given the size of the tank.   Poor water quality & dirty water   Poor water quality is another factor that can cause an increased state of stress. As fish are in direct contact with the water via their gills, they are very sensitive to fluctuations in water quality and poor water values. Dirty water, poor hygiene and/or harmful substances in the tank can therefore trigger excessive levels of stress.   Fish release harmful substances into the water themselves via their waste, but food remnants that are not removed contaminate it further. You should therefore make sure that the filter system is intact and measure/check the water values on a regular basis, e.g. using the Tetra Test 6in1.   Human handling   We humans are often also responsible for raising the stress levels in an aquarium. When we carry out water changes, transport and transfer fish, or add new fish to a tank, we can increase the creatures’ stress levels. We can also harm them due to a lack of oxygen, major fluctuations in pH value and temperature or an overly vigorous water flow.   A very unbalanced diet that does not meet the fishes’ needs or contain enough vitamins can lead to deficiencies and make fish more susceptible to diseases and viruses. An unsuitable aquarium design can be a further source of stress. Shoaling fish, for example, need plenty of space to swim, whereas other fish species prefer to be surrounded by dense plants in which they can hide.   Further stress inducers include an aquarium that is too small, lighting that is too bright and a substrate that is too light in colour. Water additives, such as medicines, fertilisers and algaecides, are also potential sources of stress and disease and should therefore be used very sparingly.   What are the symptoms of stressed fish? Pale coloring and anxiety stripes Fish in full colour If your fish are exposed to excessive or constant strains, this may weaken their immune system and make them more prone to disease. In this case, parasites, bacteria or pathogens that otherwise wouldn’t harm them could end up causing various diseases. Your aquarium fish could also exhibit weaker growth and suffer from reproduction problems. Stress can disrupt their behaviour, causing them to hide very frequently and become totally withdrawn. As well as behaving anxiously and timidly, creatures could also become aggressive, hyperactive or frantic. Other typical signs of disturbed behaviour include: clamped fins, rubbing against objects, skin changes or dull mucous membranes. Fish may even become paler in colour and start nibbling at their fins. How can I prevent stress and what are the best treatments? You should obviously take preventive measures from the outset to avoid your fish suffering from too much, or indeed any stress in the first place and getting ill as a result. One way of preventing diseases is to keep your fish in an appropriate habitat that is designed to meet their needs. Before you even purchase your fish, you should find out about their natural habitat and which species they can be kept with and which should preferably be avoided. Ideally, the fish in your aquarium should come from one continent to enable an appropriate fish stock. Furthermore, you should check the water values regularly and change the water if necessary because good, stable water values are crucial for reducing stress levels among fish. If the creatures in your aquarium do become highly stressed, it’s important to detect this problem rapidly and treat it directly. Any stress factors should be