OLL LEWIS: Maternal cultratus?

Regular readers of the CFZ blog will be aware of the saga of our Alfaro cultratus or knife livebearers. About 6 weeks ago, during the Arctic conditions of late December, the thermostat on their tank's heater broke over night. Only 2 female knife livebearers, the apple snails and 2 rather heavily bred guppies survived the cold temperatures. If one were to make a Hollywood film about the trials and tribulations of our knife livebearers you would need the next scene to be uplifting to buoy your audience back up; and just that was to happen a few days ago when at least one of the females gave birth to a clutch of tiny fish.

This was most unexpected because we thought that we would not be getting any more fry until we had replenished the tank's males, but it is possible for some female livebearers to hold on to male gametes for around a month. The only other possible explanation as to where the male DNA could have come from is the guppies and they are meant to be physically incapable of breeding with the knife livebearers, according to Max Blake.

The fish are very small indeed and whereas they are not quite the smallest livebearer young I've ever seen, they are the smallest Jon has seen and being somewhat of a livebearer enthusiast he has seen many more species than I. Given the experience of Jon and I, I would be tempted to say anecdotally that they are probably among the smallest livebearer young in the world. So small were the young that as a precaution we have moved the guppies to another tank in case they decided to snack upon the young fish. With the guppies gone Jon was most concerned that the female knife livebearers would also start to snack upon their young and his worst fears appeared to be confirmed when he saw one of them apparently chasing a baby fish, which escaped into the clump of plants in the tank. In the hope of discouraging any feeding on young I upped the amount of fishfood I was putting in for the adults on the basis that if a fish is full of easy-to-catch-and-eat flake then they won't bother going after hard to catch fast-swimming little fish. It is a technique that worked for Barnum and other showmen when they made 'Happy Family' exhibits and is still employed by some zoos and aquaria today in their community enclosures and tanks.

Upon further observation of the fish, though, I noticed that we may well have been incorrect in our initial assessment of the threat to the fish from their mothers. One female stayed in amongst the clump of plants for a long time after the births and was so well hidden that she was impossible to spot until later in the day when she moved out of the clump a while after I had moved the guppies on. I witnessed something most interesting today (3 days after the births as I am writing this blog). One of the female fish started to chase a small fish that had ventured too far out of the plant clump. Initially I thought that despite the fact that I had just put food in the tank my efforts could be for nothing if the baby fish was more appealing than the fish flake; however, as I watched it became apparent that, far from trying to eat the tiny fish, it was trying to corral the fish back among the plants eventually attempting to gently waft the fish into them as it got close.

This behaviour could have 2 possible explanations: either it was a territorial dispute between the large fish and the tiny one due to the fact that the large fish wanted first dibs on the food recently been put in the tank or it was a maternal behaviour where the fish was attempting to get her baby back into the plant clump where at this small size it would be safer than in open water. I'm leaning towards the latter explanation at present as it makes more sense than the former when you consider that even when the tank had more large fish in there there were rarely any food-related disputes, and let's not forget the action of wafting the baby back into the plant clump. It did not seem like an aggressive action on the large fish's part.

If the fish was indeed trying to protect its young from potential predators then this is quite interesting as it is generally regarded that most livebearers show very little in the way of maternal instinct, happy to just plop out their young and leave them to get on with things. An instinct for maternal care is certainly within the realms of possibility, though, as a number of the livebearers I have bread for the CFZ will often require certain conditions to be met before they breed. There are the obvious ones like temperatures but there are also ones that a surprisingly large number of people forget about like plants. Often livebearers (with the exception of some species like guppies, of which a greater challenge would be getting them not to breed so much) will require a certain amount of plants or type of plant in their tanks that can act as a nursery, protecting baby fish from the attention of larger fish, before they will breed or give birth. This shows that there is certainly some degree of maternal care in many livebearer species even if it is limited to to ensuring a nursery site is available pre-birth so post-natal care may happen more often than we give livebearers credit for.