Effect of group size on behaviour and welfare of fish

Byron

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The number of fish needed for species "x" to be healthy and less stressed in an aquarium is a topic that enters quite a number of threads on TFF. Some of us realize how vitally important the number of fish for a particular species really is, but having scientifically-controlled studies that provide concrete evidence has been largely lacking. One such study is "The effect of group size on the behaviour and welfare of four fish species commonly kept in home aquaria," authored by Amelia Saxby, Leoni Adams, Donna Snellgrove, Rod W. Wilson, and Katherine A. Sloman in the journal Applied Animal Behaviour Science, 125 (2010), pp. 195-205. This paper is available online (free) and I will include the link at the end of my post. The authors are marine biologists or similar, based in the UK, and the majority of the following is cited directly from this paper.

"Functioning-based” approaches to animal welfare aim to ensure the animal is functioning naturally on a biological level while a “natural behaviour” approach defines good welfare as being when an animal is free to fulfil its natural behaviour (Duncan and Fraser, 1997). More recently the “five freedoms” approach to animal welfare has been put forward where in order to guarantee welfare, animals should be free from: (a) hunger and thirst; (b) discomfort (an appropriate environment including shelter should be provided); (c) pain, injury and disease; (d) restriction of normal behaviour (including lack of space); (e) fear and distress (Farm Animal Welfare Council, 2009).

The welfare of four commonly kept species of ornamental fish (neon tetras, white cloud mountain minnows, angelfish and tiger barbs) was investigated in relation to group size. Behaviours including darting, aggression, shoaling and latency to feed were found to vary with group size in a species-specific manner. Each species was kept in specific group sizes in individual tanks. For neon tetras and white cloud mountain minnows, group sizes were one, two, five and 10 fish per tank; for angelfish the group sizes were one, two, three and five fish per tank, and for tiger barbs they were initially one, five and eight fish per tank.

It is important to note that for "ethical reasons," the Tiger Barb groups of one and five were removed and only the tank with ten was used; elevated aggression between groups of two and three individuals was noted as soon as they were placed together in the tank. Therefore, as holding tiger barbs at these stocking densities was likely to result in lasting harm, these treatments were terminated immediately. [Sound familiar?]

Neon tetras and white cloud mountain minnows displayed reduced aggression and darting and spent more time shoaling in the larger groups. Both species were most aggressive when held in groups of two and five. Behavioural patterns were more variable in angelfish and tiger barbs although larger group sizes resulted in increased shoaling. The results indicate improved welfare in larger groups of neon tetras, white cloud mountain minnows and tiger barbs. In angelfish, aggression was not reduced with greater numbers, but recognizing that this species naturally requires greater shoal numbers suggests that the need to defend territories or maintain social position causes aggressive actions to persist regardless of the shoal size.

I have dealt with aggression as this is a significant aspect of keeping these fish; the study delves into the other aspects which are equally interesting. There is a lot to be learned here.

 
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The number of fish needed for species "x" to be healthy and less stressed in an aquarium is a topic that enters quite a number of threads on TFF. Some of us realize how vitally important the number of fish for a particular species really is, but having scientifically-controlled studies that provide concrete evidence has been largely lacking. One such study is "The effect of group size on the behaviour and welfare of four fish species commonly kept in home aquaria," authored by Amelia Saxby, Leoni Adams, Donna Snellgrove, Rod W. Wilson, and Katherine A. Sloman in the journal Applied Animal Behaviour Science, 125 (2010), pp. 195-205. This paper is available online (free) and I will include the link at the end of my post. The authors are marine biologists or similar, based in the UK, and some of the following is cited directly from this paper.

"Functioning-based” approaches to animal welfare aim to ensure the animal is functioning naturally on a biological level while a “natural behaviour” approach defines good welfare as being when an animal is free to fulfil its natural behaviour (Duncan and Fraser, 1997). More recently the “five freedoms” approach to animal welfare has been put forward where in order to guarantee welfare, animals should be free from: (a) hunger and thirst; (b) discomfort (an appropriate environment including shelter should be provided); (c) pain, injury and disease; (d) restriction of normal behaviour (including lack of space); (e) fear and distress (Farm Animal Welfare Council, 2009).

The welfare of four commonly kept species of ornamental fish (neon tetras, white cloud mountain minnows, angelfish and tiger barbs) was investigated in relation to group size. Behaviours including darting, aggression, shoaling and latency to feed were found to vary with group size in a species-specific manner. Each species was kept in specific group sizes in individual tanks. For neon tetras and white cloud mountain minnows, group sizes were one, two, five and 10 fish per tank; for angelfish the group sizes were one, two, three and five fish per tank, and for tiger barbs they were initially one, five and eight fish per tank.

It is important to note that for "ethical reasons," the Tiger Barb groups of one and five were removed and only the tank with ten was used; elevated aggression between groups of two and three individuals was noted as soon as they were placed together in the tank. Therefore, as holding tiger barbs at these stocking densities was likely to result in lasting harm, these treatments were terminated immediately. [Sound familiar?]

Neon tetras and white cloud mountain minnows displayed reduced aggression and darting and spent more time shoaling in the larger groups. Both species were most aggressive when held in groups of two and five. Behavioural patterns were more variable in angelfish and tiger barbs although larger group sizes resulted in increased shoaling. The results indicate improved welfare in larger groups of neon tetras, white cloud mountain minnows and tiger barbs. In angelfish, aggression was not reduced with greater numbers, but recognizing that this species naturally requires greater shoal numbers suggests that the need to defend territories or maintain social position causes aggressive actions to persist regardless of the shoal size.

I have dealt with aggression as this is a significant aspect of keeping these fish; the study delves into the other aspects which are equally interesting. There is a lot to be learned here.

Great article. Emailed it to myself to read in greater depth later. Thanks for the post.
 
Any of the Characins' ( Tetras ) are best kept in large schools ideally more than 20 individuals, they do best in schools of 100 or more, but how many of us can do that.
Cichlids are talked about a lot on this forum site, I think it is cruel to keep an individual Cichlid. Cichlids are clever and do best with company. I think if you don't have a tank large enough to accommodate a group don't keep them. Also it is important to have a back up plan with these fish, so having a second tank is important.
Bettas, I have never liked the idea of keeping Bettas Full stop. The concept of keeping a fish alone for our entertainment doesn't go down well with me.

Fish have one purpose in life and that is to reproduce, if we are going to keep fish then it is important for the welfare of the fish that we give them the opportunity to fulfill their purpose of life, by keeping fish alone in a glass box is a far cry from this.
 
Any of the Characins' ( Tetras ) are best kept in large schools ideally more than 20 individuals, they do best in schools of 100 or more, but how many of us can do that.
Cichlids are talked about a lot on this forum site, I think it is cruel to keep an individual Cichlid. Cichlids are clever and do best with company. I think if you don't have a tank large enough to accommodate a group don't keep them. Also it is important to have a back up plan with these fish, so having a second tank is important.
Bettas, I have never liked the idea of keeping Bettas Full stop. The concept of keeping a fish alone for our entertainment doesn't go down well with me.

Fish have one purpose in life and that is to reproduce, if we are going to keep fish then it is important for the welfare of the fish that we give them the opportunity to fulfill their purpose of life, by keeping fish alone in a glass box is a far cry from this.
The majority of cichlids don’t do ‘groups’, especially once they’re sexually mature. They do pairs that separate themselves from others of their species.
As for giving fish the opportunity to reproduce, I agree in principle, but if you can’t find homes for all the fry it’s a terrible idea.
I fully agree with not keeping a fish on its own. Even the Black Piranha has sex once a year...
 
Speaking of cichlids I am probably going to buy this tank setup from a local guy. It has 20 cichlids in 90 gallons with a smaller sump tank. Sounds like a whole lot of fish to me. If so, I will buy other tanks. They are African & South American.
5F8BA80D-96E2-403E-BDF1-6F83F4A88601.jpeg
 
Speaking of cichlids I am probably going to buy this tank setup from a local guy. It has 20 cichlids in 90 gallons with a smaller sump tank. Sounds like a whole lot of fish to me. If so, I will buy other tanks. They are African & South American. View attachment 142001
I would be interested in knowing the different species in the tank, African and American Cichlids are very different from each other.
 
90 gallons plus the sump 20 fish should be fine. Well they are fine because there they are. It is interesting how people mix Cichlids and manage to make them all survive.
 
The majority of cichlids don’t do ‘groups’, especially once they’re sexually mature. They do pairs that separate themselves from others of their species.
As for giving fish the opportunity to reproduce, I agree in principle, but if you can’t find homes for all the fry it’s a terrible idea.
I fully agree with not keeping a fish on its own. Even the Black Piranha has sex once a year...
Cichlids actually do do groups and are happiest that way from my experience, these guys for an example
056.JPG
 
I would be interested in knowing the different species in the tank, African and American Cichlids are very different from each other.
Me too! This guy isn’t very communicative. When I asked what kind of fish, all he said was most of one group and some of the other. Forgot, but it’s in a text. Looks like me & the husband will be helping him take the it apart. He said that’s a big job. So we’ll know how to put it back together. Maybe he can tell me more then.

I would greatly appreciate suggestions on how much water to take home. We are thinking many 5 gal buckets and Coleman chests. The husband says buckets. The seller says he always uses chests.
 
Me too! This guy isn’t very communicative. When I asked what kind of fish, all he said was most of one group and some of the other. Forgot, but it’s in a text. Looks like me & the husband will be helping him take the it apart. He said that’s a big job. So we’ll know how to put it back together. Maybe he can tell me more then.

I would greatly appreciate suggestions on how much water to take home. We are thinking many 5 gal buckets and Coleman chests. The husband says buckets. The seller says he always uses chests.
I always use what we call jerry cans ( 20 liter ). Try and get about half the water if you can
 
Cichlids actually do do groups and are happiest that way from my experience, these guys for an example
View attachment 142006
Ifvyou read my post again you’ll see that I said the majority of cichlids don’t do groups once they mature, which is true. You’ve giving one species as an example of the minority that do.
 

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