Aquarium

Our large female Humbug Damsel (Dascyllus aruanus) laid eggs on the aquarium glass. Some of the eggs were collected and examined under a microscope; the eggs had not been fertilised (no visible embryo) and it is likely there are no mature males in the tank.

Towards the end of May, our large marine aquarium showed the expected increases in salinity and temperature due to the Maldives’ seasonal high ocean temperatures (31.0°C). To control the aquarium temperature, we reduced the water flow intake and occasionally added saline ice blocks on particularly hot days to give a monthly average water temperature of 27.9°C.

Fish Lab Population

High water temperatures continue to disrupt the Clownfish breeding, with lower numbers of eggs, unfertilised eggs, delayed hatchings and no new larval development. Three new breeding pairs are currently being fed plenty of krill to encourage spawning of healthy eggs.

Plankton production has remained constant, showing good health and deep pigmentation. Artemia numbers fluctuated due to indoor cooling effects, and relocating the buckets outdoors gave greater yields. Rotifer counts remain high, averaging 893/ml.

Kreisel Jellyfish Tank

We continue to rear our Moon jellyfish (Aurelia aurita) from the ephyra stage to juvenile medusa stage and we are keenly observing the anatomical and morphological advancements from 8.5cm medusae to 15cm bells. Despite the apparent simplicity of jellyfish, being composed of 95% water (and 5% protein) they experience extreme sensitivity to environmental parameters. We are currently researching the Aurelia nervous system, with relation to pulsation and navigation/orientation mechanisms.

Overall, our Moon jellyfish continue to grow steadily, albeit with some fluctuation in growth rate. We now have 33 individuals (larger than 2cm diameter) on display in our main Kreisel display tank. These individuals appeared to acclimatise well, however, their growth rate slowed for 2 weeks (perhaps feeding was more difficult due to the larger volume of water). To attempt to improve this, smaller individuals were occasionally removed from the tank and isolated for direct feeding, before being returned to the tank.

Between 21 April to 5 May, the water in the tank became cloudy, a sign of imbalance in nutrient cycling and bacteria function. At the same time, the jellyfish displayed greater bell curvature, and a reduction to 5 pulses per minute (down from the typical 8 to 20 pulses/minute). We also observed 5 jellyfish individuals completely detach the bell from their oral arm region (and they did not recover) whilst the others became inactive and shrunk in size (by 0.4cm on average). This suggests the jellyfish were stressed and not assimilating the Artemia, despite still catching and ingesting them.