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In the last week of March I noticed that one of my Gobiodon okinawae was hanging around very closely to a Pavona minuta colony and not moving anywhere else in the tank as they normally do. Taking a closer look I noticed that the under surface area of one of the branches had some eggs attached to it. They have finally decided to start breeding.
A couple of years ago, when I had a large colony of the “green weed” Acropora sp. (A. dallaswarreni ;-)) I had a pair of these G. okinawae that made their nest in the central region of the colony. They appeared to breed regularly, but due to the location of their nest it was a bit difficult to monitor what was happening. Due to a variety of reasons, I eventually lost both of those fish and have been wanting to get another two since. They have great character and love any branching type of corals. However, as a word of warning, as with any coral gobies, they can be hard on the colonies in the tank. They may nip at other neighbouring colonies to the one they take up as their home and will remove tissue from the skeleton by rubbing up against the coral with their belly. This last behaviour I think is preparing the region for laying eggs.
Last year I finally got the chance to get another two and they have been in the tank now for about 6 months. I recall reading some time ago that Gobiodon spp. individuals are hermaphrodites, so there was no concern about having to get a pair as such, just any two fish should do. And this did prove to be the case. However, there has been some research done on G. histrio which found that as juveniles they are sexually indeterminate and will sexually mature into either male or female as required or allowed (Hobbs, Munday and Jones, Social facilitation of maturation and sex determination in the coral-dwelling goby, Gobiodon histrio, Australian Coral Reef Society 79th Annual Conference, 2002). The two fish added to the tank were just two taken from a store tank that held about 6 individuals. So they weren't collected or purchased as a pair as such. If the behaviour for G. histrio holds for G. okinawae as well, then either I was lucky enough to get a male and female or they were sexually immature and formed a pair after being placed in the aquarium.
With keeping these fish, you have to make sure that the overflow is well protected. They are very small fish, so will go over in a flash if it isn't protected correctly. I made and installed a narrow comb on the top of my overflow as a prefilter so that they can't get through. It works very well and wont block up with algae etc either, since the water level in the tank would just increase and the water would then flow over the top of the blockage.
Comb shaped prefilter on overflow to ensure the gobies don't get into the weir.
G. okinaeae are very small fish, being only about 30 millimetres long. Due to their size, they keep out of the way of any other fish in the tank. A reason why the fish aren't actually eaten by fish larger than them is that they are meant to be toxic or foul tasting. Even though these two are small fish, they are very comfortable in the aquarium, coming a long way out of cover without too much hesitation. One in particular will swim out into the open water to around 30 to 40 centimetres from the reef structure. However, majority of time is spent jumping around from spot to spot on the reef structure it self and the attached corals. They can swim suprisingly fast for their size when required. There is no need to target feed them in my system, as they will happily swim around the tank comfortably. Additionally, the manner in which I feed and the water circulation within the tank means that food is rapidly blown over the entire volume of the tank. So they can pretty much hang around where every they like to grab some food as it floats past. But they do swim out into the water column with the other fish and grab some food without hesitation.
The coral they have have adopted as their nesting site is a Pavona minuta. It is the only decently sized branching coral in the tank currently, so is the only appropriate location.
P. minuta, the coral colony used for nesting by the G. okinawae
At the end of March I noticed their behaviour change and discovered the presence of the eggs. The individual looking after the eggs stays very close to them, whereas the other one is up the other end of the reef structure, about 70 centimetres away perched on top of a plating/encrusing coral (yet to identify the species). Every couple of minutes the fish looking after the egg swims over them in a wriggling motion, most likely aerating them. They location they have chosen has actually very good water moment, you can see the eggs being moved around all the time. Have not observed them actually picking at the eggs with their mouth yet, like clownfish are know to do. So unsure if they pick out unviable eggs.
P. minuta with G. okinawae eggs and the fish looking after them.
Egg location circled.
The coral tissue under the area that the eggs are attached has been removed by the fish. The coral itself doesn't appear to be too perturbed by the presence of the fish, still extending its very small tentacles and growing very well (mainly encrusting currently).
Eggs magnified slightly.
After approximately 7-10 days of the eggs being there noticed in the morning that the eggs had disappeared. So it looks like the larvae were released at that point. The next morning though, I caught them spawning again just after the lights came on. So now that I have a better idea of the incubation time and their timing, should be able to monitor their behaviour more closely and learn more. I would love to be able to see if they have sexually matured into male and female or are hermaphrodites, but there are no visible markings on them that enables me to distinguish between the two.
The spawning behaviour appears to be very similar to clownfish. One fish would wriggle over the nest area, with their belly up against the surface. They would do this two or three times, then the other fish would push in and wriggle over the surface as well. This individual would also pick at the surface with its mouth, including the locations where the eggs were already attached. I suspect the first fish is the female, as its stomach was substantially more distended than the other. Didn't get a chance to see the end of the laying, but suspect the entire process probably took about 1 hour to perform. Will now be able to observe and take notes on the entire breeding cycle, including the appearance of the eggs and behaviour of the fish. Powered by AkoComment! |
