I concur with Colin generally, but as loaches were the fish here I just want to make sure you (Kaszzaye) understand that this "greying out" is a very good thing when it comes to loaches because it is part of their inherent normal social interaction. Loaches really are incredibly social fish, as an excerpt from Seriously Fish I will cite below indicates. Fish losing colour/pattern is often due to serious stress issues, and that can apply to loaches too, but with what you initially described I am more inclined to consider it the "loach dance" grey-out.
The following is a lengthy but instructive summary for Botia almorhae but it applies basically to opther botid loaches and the Clown Loach.
Some behavioural routines exhibited by
Botia spp. have been recorded often enough that theyāve been assigned non-scientific terms for ease of reference.
For example during dominance battles (these occur most frequently when the fish have been introduced to a new
tank, or new individuals added to an existing group) the protagonists normally lose much of their body patterning and colouration, a phenomenon thatās come to be known as āgreying outā. Such displays will sometimes also happen within an established group as individuals seek to improve social ranking but are usually nothing to worry about.
Interestingly some observations suggest that the
character of the highest-ranked, or alpha, fish appears to affect that of the whole group though it must be said that scientific studies of botiid loach behaviour are virtually non-existent. It certainly seems that they display a degree of āpersonalityā with some specimens being naturally bolder or more aggressive than others, for example. The alpha is normally the largest
specimen within the group and often female.
āShadowingā is an interesting behaviour in which younger individuals swim
flank-to-
flank with older, mimicking their every movement. Some keepers report that more than one smaller fish may shadow a larger simultaneously, with even three or four on each side! The reason for it is unknown; it may relate to a group staying in touch with one another when rivers swell during times of flooding, perhaps reducing drag by swimming āin formationā or having some other communicative function. Itās been observed in aquaria with both high and low water flow and seems to be habitual to the extent whereby some individuals will shadow other fishes if no conspecifics are present.
Sound also appears to be an important factor in communication since these loaches are able to produce audible clicking sounds, these increasing in volume when the fish are excited. The behavioural aspects of this phenomenon remain largely unstudied but the sounds are thought to be produced by grinding of the
pharyngeal (throat) teeth or
subocular spines.
A further curiosity is the so-called āloachy danceā which involves an entire group swimming in a constant, restless fashion around the sides of the
tank, usually utilising the full length and height. The reasons for this are unknown and reports as to when it occurs vary but the most common triggers appear to be the addition of food, fresh water or new conspecifics, and it can last anything from a few minutes to a day or more.
