Fish Lab & Aquaria – Marine Life in the Maldives

December has been a good month for the fish-breeding program, with new protocols resulting in more consistent spawning and larval success.  The arrival of five common seahorses into Tank #32 has proved popular; they are juveniles, so it is currently difficult to determine gender (we may start to breed them when mature). The orange basslets were relocated to the main display aquarium; the new frogfish is growing well on a steady diet of adult artemia and has begun to move around the tank more.

Large Aquarium

During December, some of our fish residents sadly died, including the orange spine and powder blue tangs, a rabbitfish, and several cardinals. Post-mortems showed no obvious causes of death, although some small gill flukes were present on the rabbitfish. We have subsequently decided to repopulate the aquarium with smaller mid-water species.

The new fragments on the repaired mini coral frames are healthy and starting to self-attach. All soft corals added in November are healthy and well-adapted, although we relocated the large leather coral to give it more space.

Jellyfish – Aurelia aurita

At the start of the month, our large Kreisel display aquarium was completely emptied and cleaned, before being repopulated with four large jellyfish from our Fish Lab grow-out Kreisel system (with 362 individuals).
Water changes are maintained at 35% every two days, with a larger water change when required.

Plankton Production

Our production of algae and artemia is providing ample food for grow-outs; rotifer requirements increased, so production was scaled-up during December.

• Algae – continuing steadily on a four-day turnover, although there was a brief dip in production when one of the 2L bottles failed. This was countered within the next turnover, and has had no effect overall.
• Rotifers – Due to the increasing demand by both larvae and coral polyps, we split the current rotifer culture into two buckets, which are gradually increasing to the previous concentration. Regular harvesting has meant this is a slower process, but the recovery is continuing.
• Artemia – We transfer 100ml of two-day artemia to an 80L algae bucket every two weeks, to harvest at: the two-day stage, the two-week stage, and as full-size adults. This provides appropriately sized foods for our various marine residents.

Ornamental Fish Breeding

Following on from November, feeding frequency for breeding pairs has been increased from 2x to 3x a day, with the introduction of a prepared food ‘paste’ composed of fish, nori and pellet (we also plan to add prawn or calamari). The paste is made up of 60g fish, one sheet nori seaweed, and four teaspoons of pellet feed in hot water to promote the seaweed to become gelatinous to hold the paste together. This 200g mixture is then blended, excess water removed, and frozen into cubes (the 14 cubes last two weeks). One cube per day is defrosted in the fridge, and fed to all our fish breeding pairs, receiving positive responses. This provides more protein and fat to the brood stock fish to promote egg production, while also increasing vitamins A and C, and adding B6 and calcium to the diet – all proven to aid in proper egg and sperm formation, optimum fecundity, hatchability, and healthy development of larvae and fry.

The live food component of the diet has been increased in line with new protocols, with 100ml of adult artemia being fed to all breeding pairs every day (or every other day).

We have also tried new spawning surfaces, and a larval ‘snagger’ to move larvae with reduced stress (particularly with the damselfish larvae). The snagger was constructed using PVC pipe, a T-junction, 50um mesh, and a plastic bottle. This was then attached to the standpipe using an elastic band, and an airline was threaded through the piping (photo). This caused a flow of water to move up the piping and into the bottle; the water then flows out through the mesh while the larvae remain in the bottle for transfer. An underwater light was attached to the structure by the entrance, to lure any larvae that were missed the first time. A second attempt without an air stone on the line proved more effective.

• Amphiprion ocellaris (Common clownfish, Australia): The November batch continues to do well, with a stable population of 12 larvae that completed their metamorphosis and are now feeding on artemia (a good larval survival rate of 23%). The first rotifer feed now occurs at eight hours post-hatch (at roughly 4am). We studied the eggs under the microscope from day two to hatching, to create a development baseline to compare with other Amphiprion
  The female lays every four to six days (averaging 130 viable eggs per clutch), so we will remove the Ocellaris from the ‘breeding pair’ diet to slow production (they are a non-native Australian species, donated by an aquarist from Malé).
• Amphiprion clarkii (Clark’s clownfish): The breeding pair in tank #3 continue to produce eggs on a regular basis (every three to six days), increasing in number and quality with the new diet. One December clutch resulted in 12 larvae, which all died by day 15 (likely due to stress and insufficient growth).
  There is still an issue with parental predation of apparent healthy embryos (overnight on day five). To try to prevent this, on day five we introduced a mesh-sided box to separate the parents, while allowing water to flow (as it turned out, the flow was insufficient and we lost the eggs).
• Amphiprion nigripes (Maldivian clownfish): Several breeding pairs are starting to display mating behaviours, but we have seen no eggs this month. We are trialling new spawning surfaces (tiles) as an alternative to the pots.
• Pomacentrus pavo (peacock damsel): The two breeding pairs in tank #31 are each laying an egg clutch every six to seven days. One pair has used the PVC pipe as a spawning surface, which makes for easy collection of the larvae. (An air stone is placed under the pipe to maintain aeration of the eggs).
  The second pair has colonised the standpipe, and so egg collection is performed using the larval snagger. Despite success in hatching and collection, all clutches were gone by day three, likely due to inappropriate foods. The smallest food we currently produce is 80um rotifers, but pavo larvae feed on copepod nauplii (7-70um), so we have ordered some Thalassiosira weissflogii diatoms (7-20um).
• Stenopus hispidus (coral-banded shrimp): One batch of eggs hatched successfully, resulting in a number of first-stage nauplii (which were subsequently lost). Mating behaviour and moult were observed, and eggs are now visible as a blue tinge in the female, so another clutch is expected shortly (12 days after appearance of the eggs).

Aquarium One

This month, two colonies of bubble coral (Physogyra lichtensteini) donated by our Dive Team colleagues were introduced, and are now fully adapted.

• Mini coral frame – continues to show good health.
• Maldivian clownfish – has now settled on one anemone, and continues to grow and mature.
• Sea star (Linckia multifora) – has shrunk slightly, and appears less healthy this month.

Aquarium Two

• Corals – The Goniopora coral colony continues to thrive, but out of the five mushroom corals introduced last month, only two remain in the aquarium as the resident crabs constantly take them under the rocks!
• Coral banded shrimp – remains healthy and is feeding properly; the new convict tang (Acanthurus triostegos) and green chromis (Chromis viridis) have settled and started to grow.
• Mini coral frame – coral fragments continue to grow and encrust.
• Clark’s clownfish – laid eggs four times this month (at around 1430h); all eggs completed their development and hatched overnight. We are following the embryonic development.