Dr Alex Jordan, of the University of New South Wales, Australia, takes a look at the interesting social life of the Tanganyikan cichlid Neolamprologus pulcher.
Neolamprologus pulcher is endemic to Lake Tanganyika, a region in which fish have filled the majority of ecological niches. Perhaps as a result of competition, the fish there have evolved a wide range of interesting life histories.
N. pulcher is rare among lake fish because it lives in groups with ‘helpers at nest’ — non-breeding individuals that help rear the brood of the dominant pair as well as undertaking territory maintenance and defence. This is known as alloparental care.
Are group members related?
Relatedness within groups is quite low on average, with large males usually the most distantly related to others in the group.
Obviously when born the young are related to their parents, but as they mature they typically move away from their natal group into a new one.
What affects their choice as to what group to join?
I have been conducting experiments in Lake Tanganyika looking at factors that influence the decisions dispersing helpers make when joining new groups.
These include social rank in the new group, because access to food, shelter and mates depends on social position, likelihood of acceptance or rejection — and external factors such as predation risk in different groups.
What challenges do they face when they join a group?
N. pulcher are very territorial so visitors to groups are often vigorously driven away. There is evidence that fish visit a group many times before attempting to join it, perhaps to become familiar with the group’s members, which may reduce aggression.
In my own experiments I expected N. pulcher to join groups in which they would be most senior and therefore receive the least aggression — but they did quite the opposite!
When I gave the fish a choice between groups of smaller or larger helpers they chose those with larger helpers, thereby accepting a lower social rank and receiving far more aggression.
It seems they tend to pick groups offering the greatest safety from predation, even though they receive aggression from their own species as a result.
How is their chance of breeding success affected and what does this research show?
By joining lower down the ranks the new fish have a longer wait to obtain a breeding position and also possibly reduced access to food, which would further slow their growth.
However, they are likely to enjoy higher survival rates in groups of fish larger than themselves, so it might seem a well thought out trade-off to lay low for the time being and surviving as against going straight to the top and probably getting eaten before getting a chance to breed.
This result demonstrated a very complex reasoning process in these groups, which is not entirely unexpected given the complex social structure of N. pulcher groups.
Is it possible to keep Neolamprologus pulcher in social groups in the aquarium? If so, how do I go about it and what's the minimum sized tank I would need?¨
It certainly is, but if you have too small a tank you will soon see a darker side to the inappropriately named 'Princess cichlid'!
Both N. pulcher and N. brichardi form extended social groups in the wild, but there is often conflict within these groups, and members join and leave periodically.
In the wild this isn’t a problem as the lake is big enough for them to move away, but in captivity if a group member wants to leave, or is forced out, they may have nowhere else to go. Indeed, even in a 180cm/6' tank it would be difficult to peacefully maintain two separate groups of N. pulcher.
For a single group I would suggest no smaller than a 90cm/3' tank, but given that groups in the wild can be as large as 15-20 individuals, you might be better with an even larger tank.
To form a group, first make sure you have a pair (obtained most easily by rearing a group of young and waiting for the first pair to form, then removing all others), and then wait for them to spawn.
As they grow, remove most of the young, but leave some behind to help rear subsequent broods.
You could try to introduce smaller adults to the tank with an extablished group, but in my experience in aquaria and the wild, the pair will probably react very aggressively and may kill the newcomer, so be careful! Otherwise enjoy keeping a marvellous natural spectacle.