Throughout December and January, we have been very busy refurbishing our large marine aquarium (dimensions: 3.3m x 1.04m x 0.9m, totalling approximately 3 cubic metres (108 cubic feet).
In aquariology, there is a “Fish only” [FO] aquarium and “Reef” aquarium [R] whereas we were developing the more complex “Fish-only with live rocks” aquarium [FOWLR]. This latter type is designed to showcase fish along with living corals naturally colonised by a variety of marine life (sponges, invertebrates, beneficial nitrifying bacteria). This creates a natural-looking environment and provides excellent supplemental filtration to help maintain a stable eco-system. Usually, a FOWLR aquarium does not contain living corals or invertebrates as these may get eaten by the fish, so to prevent this we will be feeding the occupants daily with a variety of foods.
- Create a safe environment for marine life, staff and visitors;
- avoid stagnant water and sedimentation areas; easy to clean and to keep clean; hide pipes and pumps;
- representative of Maldivian waters.
Options – materials for the aquarium background
- Expanded polystyrene (inexpensive, but artificial in appearance and not durable);
- prompt natural cement [PNC] (porous, lightweight and easy to model, but not available in Maldives);
- grid with stones (natural elements, but heavy and bulky installation with sedimentation areas);
- polyurethane foam (natural in appearance, durable and lightweight, but expensive and potentially toxic).
From these potentials materials, we choose to make the background with “polyurethane foam”, which is commonly used in public aquaria (as well as in home furniture). This foam is made from two separate ingredients that harden when mixed together and allowed to dry. Before drying, the foam can be modelled and shaped to cover the walls, hide technical equipment and give a natural appearance. Whilst modelling, we were careful to keep the thickness of the foam to a minimum (<10cm) to allow the maximum space for the fish to swim around. Finally, to neutralise any potential toxicity of the foam, we applied four coats of “Epoxy resin”, commonly used in marine aquaria for waterproofing.
Basic schematic showing aquarium dimensions
Carla and Aku hard at work
The live-rocks were taken from different places of our house reef, and we mainly chose dead coral plates and porous stones. We drilled the coral plates and supported them around a central PVC pipe acting as a supportive column.
300kg of sand was taken directly from the sea to keep its biological benefits. We then added soft and hard varieties of living corals, along with anemones and other marine life beneficial to the ecosystem. We chose different species of corals, sponges and ascidians, to represent Maldivian biodiversity. Crustaceans, echinoderms and molluscs were also added, to facilitate in the tank cleaning process and help to create a balanced and stable ecosystem.
The fish population was carefully selected according to temperament, ability to live together and biological function in the food chain. We avoided carnivorous predators and chose smaller sized fish – a mixture of filter-feeders, detritivores, herbivores and omnivores. Once the fish were caught, we acclimatised them in our turtle pool to become accustomed to dry foods and a closed environment. Aggressive fish and those which did not acclimatise well were returned back to the sea. (As a bonus, having fish in the turtle pools was also beneficial for our rehabilitation turtle residents, as they keep algal growth under control and remove parasites from the turtles).
The Construction and Refurbishment Process
Sample of fish caught (left, click to enlarge)
Maori wrasse (* top), Picasso triggerfish (left),
Brown butterflyfish (middle), cleaner wrasse (left-middle),
Regal angelfish (right), Emperor angelfish (bottom),
Honeycomb grouper (* bottom right).
(*) The grouper and the Maori wrasse were released due to their size and predator function.
– Acropora species, Cap-like mushroom coral (Halomitra pileus), Porites species, Artistic coral (Platygyra daedalea).
– Green Pavona (Pavona maldiviensis), Angular coral (Favites halicora), Sun coral (Diploastrea helipora), Flower-pot coral (Goniopora species).
– Bubble coral pearl (Physogyra species), Blue coral (Heliopora coerulea), Mushroom leather coral (Sacrophyton species), Long-lobed cladiella (Cladiella species).
– Sea anemone (Heteractis magnifica), Sponge (Acabthella klethra), Red pencil urchin (Phyllacanthus imperialis), Mathae’s sea urchin (Echinometra mathae).
– Sea star (Choriaster granulatus), Giant clam (Tridacna squamosa), Sea cucumber (Isostichopus badionotus), hermit crab (Dardanus lagapodes).
– Picasso triggerfish (Rhinecanthus aculeatus), Blotched porcupinefish (Diodon liturosus), Crescent perch (Terapon jarbua), Emperor angelfish (Pomacanthus imperator).
– Blue-streak cleaner wrasse (Labroides dimidiatus), Maldivian cardinal fish (Apogon maldivienses), Saddled pufferfish (Canthigaster valentini), Brown tang (Zebrasoma scopas).
Updates February 2017
On 12 February, we upgraded our pumps to more powerful models, so now the tank volume is renewed every 1.5 hours, giving us a better supply of oxygenated water. We also introduced some new inhabitants this month:
- White-spotted pufferfish (Canthigaster janthinoptera)
- Adorned wrasse (Biochoeres cosmetus)
- Six-spots sleeper-goby (Valencienna sexguttata)
- Bird wrasse (Gomphosus caeruleus)
- Imposter blenny (Plagiotremus phenax)
- Monocle bream (Scolopsis bilineata)
- Eye-line surgeonfish (Acanthurus nigricauda)
- Crested sabretooth blenny (Petroscirtes mitratus)
The water parameters are checked daily, and remain safely within the range for the health of our aquarium inhabitants.
Updates March 2017
Throughout March, the coral life in our aquarium remained stable, except for Acropora and Pocillopora species which showed some bleaching. Using a stronger light to increase the activity of their zooxanthellae (which provide 90% of their energy) did not help, so we chose to transplant them onto our coral frames out in the lagoon. The soft corals which were the most affected in January and February have now recovered.
In aquariology there are 3 different filtering methods:
- Mechanical Filtration (foam, sand, bag): the first step, trapping organic matter particles suspended in the water avoids sedimentation in the tank [we use: 4 sand filters (10μm) followed by 4 ultrafiltration filter bags (5 μm)].
- Biological Filtration (ceramic, bio-balls, living stones): bacterial action transforms dissolved organic matter to cycle Nitrogen [we use: living stones inside the tank].
- Chemical Filtration (charcoal, zeolite, ultraviolet): to modify the chemical parameters of water. Activated charcoal removes organic dyes; ‘green’ water is sterilised with UV [we use: a UV filter].
In order to maintain good water quality in the aquarium, we perform regular cleaning tasks ranging from daily backwashing to annual sand filter cleaning. During March, we cleaned 2 of the 4 sand filters. Each filter contains 450kg of sand, and it took 2 full days of hard work to clean all of the sand from just one filter. We also discovered that some fish had made a home in the filters! (The two puffer fish were moved to our aquarium).
Aquarium – new arrivals
- Long-nose filefish (Oxymonacanthus longirostris)
- Yellow-tail basslet (Pseudanthias evansi)
- Two-colour cleaner wrasse (Labroides bicolor)
- Turn-worm blenny (Plagiotremus rhinorhynchos)
- Two-colour combtooth blenny (Ecsenius bicolor)
- Lined soapfish (Grammistes sexlineatus)
- Red fire-goby (Nemateleotris magnifica)
- Yellow-head butterflyfish (Chaetodon xanthocephalus)
Updates April 2017
Throughout April, we recorded an increase in water temperature of our large marine aquarium. Water is pumped directly from the sea, and as the seasonal ocean temperatures have risen, so too has the temperature of our tank. The average sea temperature for April is 1.4°C higher than last month, with a maximum value of 30°C recorded on 19-20th April. Thankfully, in the controlled conditions of our aquarium, it is relatively straightforward for us to lower the water temperature with a water chiller or simple ice bucket, and the coral life remains healthy and stable. However, the corals and marine creatures out in the lagoon must cope with and adapt to the increased water temperatures on their own…
We recently caught and released our small Honeycomb grouper (Epinephelus merra) after 4 months, as we think this predator was responsible for the disappearance of some of our aquarium’s smaller occupants! In addition, our Porcupine fish (Diodon liturosus) sadly died after 89 days, maybe due to lack of food (we manually feed during the daytime, and this fish is nocturnal). We also noticed our six-spot sleeper gobies were looking skinny, maybe through a lack of nutrients; these limnivorous (mud-eating) fish need a rich soil substrate, so we decided to put more food at the bottom of the tank.
Some of our new inhabitants this month include:
- Green puller (Chromis viridis)
- Arrow goby (Ptereleotris evides)
- Wrolik’s wrasse (Platyglossus chrysotaenia)
- Moon wrasse (Thalassoma lunare)
Our infamous Honeycomb grouper (Epinephelus merra), before release
Updates May-June 2017
In response to the rise of ocean seawater temperatures observed in April-May, the coral life in our main aquarium was affected –
- Favidae has some necrosis but is globally recovering its green colouration;
- Halomitra and Platygyra species have started bleaching throughout May;
- Porites is now in intermediate condition, part-covered by filamentous algae;
- Poicilopora (re-introduced last month) is recovering from bleaching.
In addition, we introduced a new anemone (Heteractis aurora) found at Madhirivadhoo reef, and another soft coral (Sacrophyton sp.)
With the help of the water sports team, we caught 57 new fish during three 2-hour fishing excursions. We now have a school of Orange Basslet juveniles and different juvenile wrasse species, known to be peaceful in captivity. Our aquarium volume is 3 cubic metres, so to avoid any oxygen problems (tank anoxia) we are careful not to exceed a total fish biomass of 30 kg.
- Orange Basslet (Pseudanthias squamipinnis)
- Coral Hogfish (Bodianus axillaris)
- Many-spined angelfish (Centropyge multispinis)
- Peacock flounder (Bothus lunatus)
- Chestnut eyelash blenny (Cirripectes castaneus)
- Oriental sweetlips (Plectorhinchus vittatus)
- Nudibranch (Phyllidia varicose)
- Blue-ribbon wrasse (Stethojulis trilineata), Checkerboard wrasse (Hemitautoga hortulanus), Speckled wrasse (Anampses meleagrides), Dusky wrasse (Platyglossus annularis), Queen rainbow wrasse (Allocoris formosa), Checkerboard wrasse (Hemitautoga hortulanus), Exquisite wrasse (Cirrhilabrus exquisitus), Splendid leopard wrasse (Macropharyngodon bipartitus).
Updates July 2017
The increased water temperatures recorded in the aquarium during the last three months have negatively affected the coral life. Some of our coral species (Agaridae, Porites, Platygyra) have shown necrosis and algal growth. The newly introduced Pocillopora colony has also developed some algal growth and our bleached Halomitra (Cap Coral) specimen was returned to the ocean. By contrast, the Acropora specimens have been growing well, which is interesting as this species was the most affected by the 2016 coral bleaching event.
Certain fish species are unsuitable for life in the aquarium, and need releasing back into the ocean after several weeks. This catch-and-release is a lot of work, but provides a showcase to increase public awareness of our diverse Maldivian reef fish. The current population size is 104 fish, and recent new arrivals include:
- Tall-fin Batfish (Platax teira)
- Moorish idol (Zanclus cornutus)
- Powder-blue surgeonfish (Acanthurus leucosternon)
- Long-nose butterflyfish (Forcipiger flavissimus)