A continuation of ‘Flying Elephants’: a story was never evidence, but now even photographs and videos need a documented origin. What counts as evidence in the age of artificial intelligence?

Not answers, but principles for finding them.

FMC can be useful, but simply bathing the fish proves very little. We examine the origins of the mixture, formalin and FMC regimens, the relationship between dose and exposure time, and how treatment becomes ritual when the drug replaces the clinical question.

Flashing is observable behavior, while “itching,” “gill irritation,” and “parasites” are already explanations. We examine what can actually be observed, which conclusions genuinely follow from the fish’s behavior, and where a familiar phrase turns into an unproven causal model.

A practical view of the scientific method: how to avoid being confidently wrong and distinguish knowledge from assumption.

When some reagents are unavailable, an examination is not necessarily useless. What matters is understanding the function of each step, the information it provides, and which conclusions are no longer justified if that step is omitted.

Granulomas do not necessarily mean mycobacteriosis. Shape, size, necrosis, and capsule development characterize a pathological process but do not identify its cause. Using examples of different lesions in fish, we examine the limits of morphological diagnosis and the danger of turning observations into ready-made diagnoses.

Health is not the absence of all microorganisms and parasites, but the ability of an organism to preserve its functions and resilience while continuously interacting with the environment.

In severe cryptocaryonosis, the first task is to keep the fish alive and reduce the number of parasites on its body; only then should the remaining life cycle of Cryptocaryon in the system be targeted.

A practical approach to fish necropsy: what is normal, what may be variation, and what indicates pathology.

Oocysts with elongated sporozoites are characteristic of Goussia. Microscopy-based interpretation and diagnostic features.

Not everything with a capsule is Cryptococcus. Morphology may resemble it, but conclusions require caution.

Hyphae in fish are not always saprolegniosis. It is important to distinguish colonization from invasive processes.

The examined fish showed no visible signs of disease during life. Mortality occurred predominantly at night. Gills were pale, and the fish were slightly emaciated. Necropsy revealed granulomas in the spleen and/or kidneys. Parenchymal organs were enlarged and anemic. The gross appearance was consistent with mycobacteriosis. However, Ziehl–Neelsen staining of impression smears from spleen and kidney did not reveal acid-fast bacteria. The granulomas were necrotic, a feature commonly associated with mycobacterial infections. ...

Intracellular microorganisms in fish: morphology, localization, and diagnostic interpretation.

Toggle Myth / Reality Fin Rot Is a Common Bacterial Disease Fin rot is considered one of the most common diseases of aquarium fish. Almost every aquarist encounters this problem sooner or later. The disease is usually believed to be easy to recognize even without special equipment. The main symptom is the destruction of the fins. At first the edges of the fins become uneven or frayed, then they gradually shorten. Sometimes the edges appear whitish or cloudy, and in more severe cases redness may appear at the base of the fins. ...

Fish do not need hexamitids. Parasites need fish. Why outbreaks are linked to introduction and imbalance rather than ‘activation’.

Toggle Myth / Reality Ichthyophthirius is present in every aquarium. This parasite is believed to be permanently present in the system and becomes active only when environmental conditions deteriorate. Stress, temperature drops, water changes, or conflicts between fish are thought to activate a parasite that had previously remained in a dormant state. It is widely accepted that Ichthyophthirius forms highly resistant cysts capable of persisting for long periods in substrate, filters, and decorations. Even after prolonged absence of clinical signs, the infection is assumed not to disappear but merely enter a latent phase. ...

Non-lethal fish diagnostics explained: why scrapes, smears and examinations are safe — and why severely compromised fish may die after handling.

If fish are dying in the aquarium for unknown reasons: Transfer all fish to another tank. Investigate what is happening. Mass mortalities can vary: Different species are dying simultaneously. Different genera and families have distinct lifestyles, physiology, and immune responses. If multiple species die at once, the cause is more likely water chemistry rather than a pathogen. One species dies quickly and massively. This is also often related to water chemistry — the most sensitive species reacts first. ...

Surgical Procedures on Aquatic Animals under Anesthesia: Gentle Technique and Cosmetic Suturing Precision and a gentle approach are critical in fish and aquatic animal surgery, especially for rare or valuable specimens. Standard “mattress” or rough sutures commonly used in hatcheries are not suitable—they increase the risk of complications, necrosis, and wound dehiscence. Operating Table Setup The main water box with a pump ensures a constant water flow. The working table has a cutout for positioning the fish on its back. The pump tube is inserted into the fish’s mouth, and water flows over the gills. Wet cloth covers the fish to prevent drying. An anesthetic is added to maintain the animal in a stable state throughout the procedure. The dosage of clove oil is 0.35 ml per 10 liters. Such fish are very sensitive to it. ...

Toggle Myth / Reality Myth “Only Fresh Fish Can Be Examined” There’s a common belief that if a fish dies in an aquarium, an autopsy is pointless. It’s often claimed that you must dissect immediately after death, otherwise nothing useful can be learned. The reasoning goes like this: fish decompose very quickly at room temperature — within minutes, tissues change, organs lose structure, and parasites either die or abandon the host. ...

The “perception loop” of medications: enthusiasm → widespread use → side effects → fear and rejection → rational balance. It’s time to move on to the final stage… Toggle Avers / Revers Medications as a Lifeline Methylene Blue Antiseptic and mild detoxifier. Supports tissue recovery and oxygen balance. Useful for diagnostics and treating fry. Methylene blue is one of the safest and most accessible dyes in fishkeeping. It helps in cases of nitrite poisoning, improves tissue oxygenation, and acts as a general antiseptic. Used for treating fungal infections on eggs, for short baths, and diagnostic staining. Easy to prepare, easy to use — even for delicate or juvenile fish. ...