Shoaling: species number, behaviors, and science

Tifftastic

Tifftastic

"With your powers combined . . ."
Sep 9, 2008
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Now that I have completed, and submitted my dissertation and am only still running on the fumes of yesterday's energy drinks to stay awake long enough to help a few of my buddies with finalizing their work, I thought I would take this time to talk about what I have already read about shoaling behavior in experimental environments. Most of this relates to startle behavior, and I have a few different species that have been studied.

I'll try to keep these small. But this comes from a comment on this thread, discussing what is an appropriate school size and how we know that. Basically, are we just assigning an arbitrary number? Since I am currently researching something similar to this, I thought I would share what I have learned. Here's the quote:

wesleydnunder said:
There are some "must-nots" and "musts" which have crept into the hobby over the years which most folks will parrot for lack of a better reason than they read it somewhere on the internet. Examples:

1. For a schooling species, you "must" always keep at least SIX of that species. The thinking behind this reasoning is that schooling species form large schools in nature as a defense mechanism. The constant movement and densely-packed cloud of fish confuses predators and increases an individual's overall chances of surviving to reach the breeding phase of its life. It stands to reason that this behavior is instinctive and follows the species from the wild to the aquarium. These fish seem more "comfortable" with members of their own kind. Thanks to one of OrionGirl's contributions to this thread, we get an idea of how some of our "rules" come into being. But why the number 6? Why not 5...or 7? ...or 20, for that matter? Did anyone ask the fish? Has anyone put a particular schooling species into a very large tank and, starting with one fish, added individual fish of that species and studied the behavior of the school? . . . .
Click to expand...

*Please try not to judge if my sentences get jumbled, I am running on an average of three hours of sleep a night for the last 2 weeks. Just one more night and then it's time for a break and an absolutely fantastic night out.

Shoaling in guppies:

  • Group demographics: 10 feral individuals in each group, all comprised of a single sex
  • Methods: Individual measures
    • Boldness: starting box with a lid on a pull in an environment that the fish had never been in. Lid lifted, and the time it took the fish to emerge from the box into the novel environment was recorded. The shorter emergence time, the bolder the fish.
    • Activity: number of crosses over a grid line in a ten minute period
  • Methods: Sociability: 6 unfamiliar female guppies placed in tank where they could see, but had no physical or chemical contact. sociability was measured as the time in 10 minutes that the fish spent in proximity of the shoal
  • Methods: Group exploratory behavior: Three "pools" separated by "riffles", create by connecting three fish tanks. Two shoals made of 2 males and 2 females each, position of each fish was recorded every twenty minutes.

    Having identified that key individuals within the group control
    exploration tendency, when then examined how these individu- als contributed to social dynamics as the fish moved around in the flume. To do this, we tabulated how often singletons were observed, how often all 4 fish were found in the same compartment, and the mean elective group size of each shoal over the observation period
    Click to expand...
Conclusions:
Surprisingly, no significant correlations were found between group exploratory behavior and any of the group mean personality scores (boldness, activity, and sociability). Rather, the exploratory behavior of the shoal was controlled by the personality traits of key individuals within the shoal
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Brown, C. & Irving, E. (2014) Individual personality traits influence group exploration in a feral guppy population. Behavioral Ecology, 25, 95–101.

Essentially, this study suggests that what is important in group dynamics is having a bold individual in the group. Even in small groups, a bold fish will encourage others to explore and be less wary of new environments.

I plan to keep adding to this thread as I gain more info and have more time. Hopefully will include my own research not too long from now.
 
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Following this with barely-contained enthusiasm.

Mark
 
Just out of my limited experience, I've found schooling behavior to be more displayed when there is a "threat". That is, even in a small group of say 3-5 tetras, they will venture out alone frequently when alone. Introduce a larger fish (even in my current case with a GBR and 3 black neons) and the tetras will rarely be found by themselves.
 
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This has been scientifically suggested to the basis for the evolution of schooling/shoal/group/flock behaviors in animals. Those that exhibit the antipredator defense of grouping, reduce predation by risk dilution, predator confusion and other means. This means that animals that have disposition that increases their conspecific social behaviors will have increased survival and pass those traits on to their offspring. Additionally, this behavior reduces the energetic costs associated with predator detection (observatory behavior can be split between members of the group) and all individuals will have increased amounts of energy that can be allotted to foraging and finding mates, again increasing the chances of reproducing their genetic "stuff."
 
Wow, interesting topic and cool of you to stay up late and help out your friends.

I have a school of 4-5 inches SD's regular silver dollars and they would shoal together from time to time but disband once in a while. My big 9 inches oscar would reign around the tank and before you know it, the oscar gets a little close to them and sometimes they start shoaling away along with my tinfoil, red hook SD.. definitely like to know more about the science of shoaling! Subscribed haha.
 
Tifftastic said:
This has been scientifically suggested to the basis for the evolution of schooling/shoal/group/flock behaviors in animals. Those that exhibit the antipredator defense of grouping, reduce predation by risk dilution, predator confusion and other means. This means that animals that have disposition that increases their conspecific social behaviors will have increased survival and pass those traits on to their offspring. Additionally, this behavior reduces the energetic costs associated with predator detection (observatory behavior can be split between members of the group) and all individuals will have increased amounts of energy that can be allotted to foraging and finding mates, again increasing the chances of reproducing their genetic "stuff."
Click to expand...

Curious, and way under schooled on the subject, to be up front. Are you suggesting that no threat is needed? Or the schooling behavior is exhibited until a "safe" atmosphere is concluded? I've introduced much larger fish to big tanks of numerous small schoolers/shoals, who had been in there so long they never did. Instant school/shoal and they began exhibiting level characteristics.
 
The research is still ongoing an much of what I have been reading is brand new 2015/2014 research, but essentially there is still a bit of a lack of understanding of group level behaviors in fish and other mammals. But here is what is thought as of now:
  • Group behaviors and cooperation evolved, essentially, to increase survivorship and reproduction (both are accounted for in the term "fitness" that you hear from Darwinian evolutionary theory).
  • Evolution will "favor" traits or characteristics that increase fitness, because those individuals will survive longer and reproduce more, transferring there genes to future generations.
  • The favoring of group behavior in some species has led them to evolve to have a genetic predisposition to "desiring" to conform to a the group. These individuals will likely produce offspring that also desire to conform to the group.
  • The strongest form of this desire is exhibited in fish that shoal and birds that flock.
  • Additionally, these animals can learn shoaling/flocking behaviors by observing others in the group and conforming to their behavior.
  • Lastly, shoaling behavior, as it is a predator avoidance behavior/threat response, will be exhibited more strongly when the fish are presented with a novel environment or a threatening stimulus.
This is just the basics and there is much more work to be done, but basically what the research is suggesting is that shoaling is an avoidance behavior for risky situations. The fish are always aware of where others in the group are, through means sensations on the lateral line and possibly chemical and olfactory cues, but may not school/shoal very tightly unless a stimulus is present.

*I'm also working on summing up another article relating to this at the moment.
 
Interesting...so you can conclude things without the stimulus present?
 
Camera riggings in a natural environment have allowed for the measure of the average distance between individuals (nearest neighbor distance or NND) in shoals of fish. It has been suggested, again work is still being done, that in most species the NND is about 1.5x the body length of the fish. Measures after a startle, in the presence of a predator, or when being placed in a novel environment in the lab indicate that the distance will be much less (statistically significantly less) than in an environment where their is a threat, or the environment is unfamiliar. I actually have a really good paper on that, and maybe I will summarize that one first. . .
This has also been studied with communal spiders and bird flocks and I think I have a paper that talks about minks and rodents.
 
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