Fish Lab & Marine Aquaria

Clownfish Breeding

During February, we recorded 2 spawning events from each species; our breeding pairs of Clark’s clownfish (Amphiprion clarkii) successfully produced 500 larvae, but the parents of the Maldivian (Amphiprion nigripes) and Common clownfish (Amphirion oscellaris) ate their eggs.
The first spawnings of all 3 species produced weakly coloured eggs and low hatching rates, possibly due to unmet dietary requirements. After introducing krill into their diets, the second spawnings produced much better-quality eggs, so we are currently revising their diet plans.

This month, we also collected 3 new breeding pairs of Maldivian clownfish from anemones on the house reef.

Large Aquarium

During February, we collected a variety of fish for our main display tank, with more to come in the following weeks. Our current focus is to introduce more bottom-feeding species to clean up the algae, namely gobies (Valencienna sexguttato) and goat fish (Mullidae). We will also be increasing the numbers and varieties of brightly coloured fish species to create an authentic representation of a Maldivian reef.

• Black eye rabbitfish (Siganus puelloides) – With a diet of sponges, tunicates and algae, they are often found on algae-rich reefs.
• Checkerboard wrasse (Halichoeres hortulanus) – Capable of changing appearance and sex depending on environment and reproductive needs. Native to the Indian ocean and central Pacific.
• Emporer angel fish (Pomacanthus imperator) – First identified in 1787, this species has been a favourite due to its elegant colours, earning it the imperator title. Their appearance changes so much, that the juvenile stage was considered a different species until 1933.

Small Aquarium One

A new zoanthid colony (Zoanthus mantoni) was added at the beginning of the month, and a new mystery juvenile Maldivian clownfish (Amphiprion nigripes) has appeared! The giant fluted clam (Tridacna squamosal) was removed, as it was growing very large and remained unattached to the substrate (presenting a hazard to other occupants).

Our mini coral frame of 26 fragments now has 21 fragments encrusted over their zip ties plus 1 fragment still to encrust (5 fragments show some dead tissue). The 4 fully dead fragments have now been replaced with other Acropora species.

Small Aquarium Two

The Clark’s anemonefish (Amphiprion clarkia) have laid eggs again twice this month, which we have harvested to observe under the microscope. For the first two days, the eggs show little development in situ, maintaining the homogenous yellow colour of the yolk sac. By Day 4, the eggs had visible muscular contractions and heartbeat, which was previously not observed until Day 5, and indicates that the eggs undergo rapid non-linear development between Days 3 to 4. In the aquarium, some eggs appear to hatch by Day 7 or Day 8, when the larvae either get eaten or swept into the outflow, so they cannot mature.

Our mini coral frame now has 12 fragments encrusted over the zip tie; 1 fragment is partially bleached and 1 fragment is dead. In general, the fragments appear to have a similar success rate in both the aquarium and out in the lagoon (albeit with a very small sample size of just 2 mini frames). This is surprising, considering the aquarium mini frame has fewer obvious limitations to growth compared to the lagoon (for example: sedimentation, predation, breakage from wave action).

Linckia multifora sea stars

SS1 (large specimen) – appears to have lost an 8mm portion of one arm. This could be part of the sequential loss of parent arms for asexual reproduction, commonly seen in this genus and previously observed by our team. It is, however, typically the largest arm that autotomises, resulting in loss of the whole of the arm (Crawford 2007). So in this instance, the missing arm portion may have been predated by another individual in the aquarium (perhaps the mantis shrimp).

SS3 (large specimen) – slight decrease in average arm length this month of 0.2mm. With continued decrease in growth rates the past few months, this now puts SS3 at the same average arm length as October 2019 when it was 32.8mm. It could be that growth rates are stagnating as the sea star reaches its maximum size, and may indicate that it will soon donate a new arm.

SS4 (autotomised arm) – average increase of 1.2mm this month, and although the parent arm again decreased in size by 2mm, it continues to differentiate its new arms into the ‘comet-phase’.

School Visits

As part of the Manta Trust’s “Ocean School” awareness program, our Landaa team had the pleasure of welcoming the lovely students from Kamadhoo school. The 25 students spent the afternoon at our turtle rescue centre, learning about our marine conservation programmes, and had an interesting hands-on experience transplanting their own coral frame.