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/A Diversity of Aquatic Life

Keeping Planktivores Fed

Foods and techniques for keeping the bellies of predominately plankton-feeding fishes full


 Bob Fenner    


            Likely more than half the species of fishes we keep as saltwater hobbyists are planktivorous feeders in the wild, relying on currents and hapless invertebrates in the water column for sustenance. Think about this. Popular groups like the Fancy Basses (Anthiinae), Fusiliers (Caesionidae), most of the Damselfishes (Pomacentridae) and Butterflyfishes (Chaetodontidae) are principally planktivorous.


Here in Fiji, a shoal of Lyretail Anthias, Pseudanthias squamipinnis bobs in the upwelling current, catching their planktonic fare along with the opened Nephtheid soft corals.


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            While it is certainly known that most all planktivores can and will learn to accept other fare, formats of foods in captivity, a good deal is lost in not providing such foodstuffs on a regular basis. Colour, growth, behavioral activity and likely reproductive fitness all suffer from a lack of “plankton”.

            Providing this fodder is not a difficult proposition. Much can be done easily by aquarists to promote and deliver these organisms, live even, let alone as dried, frozen/defrosted and other formats (palatable pellets, extruded sticks…) can be proffered a few times daily during “light hours”, when these fishes by and large are actively seeking such foods.

            Better still are methods of providing live planktonic foods on a punctuated basis several times daily. Some novel gear exists or can be fashioned DIY to store and meter out aliquots of dried planktonic foods or fluid, including metering systems with timers to simple in or out-of tank reservoirs that pump or drip into your main/display tank w/ a mix of foods suspended in solution.

Plankton: Some Definitions

            Classically plankton has been defined as any organism in the water column that can’t locomote any faster than the currents that push it about. Investigating this huge mass of material reveals it to be made up of microscopic Viruses and viroids, Monerans (bacteria, funguses, Blue-Green Algae), Protists of all sorts including algae and protozoans, Metazoans (animals) with most all phyla represented, and importantly, sex cells (gametes) and many MANY tons of their intermediate (and planktonic) developmental life stage individuals. Think how many groups and large species are dependent on this floating biomass for sustenance… the three largest fishes (Whale and Basking Sharks, the Manta Ray), the largest whales (baleens), including the Blue, the largest animal to ever have occurred on this planet, the myriad sponges, sea squirts, and most all stinging-celled life (“corals” to hobbyists) derive the bulk of their nutrition from planktonic sources, nearly all larval marine fishes are planktivorous as well as planktonic...

Phyto- Zoo- Who Knows Nano?

            Algal plankton, as opposed to benthic (i.e. attached on the bottom) is called phytoplankton. Animal types, mostly crustaceans, worms and mollusks to aquarists are zoo-plankton. Plankton is also characterized/classified according to size, and this can be extremely important, as their potential predators often can only catch/sieve a given range. They are further delineated by various aspects of their biology (e.g. bioluminescence)…

Planktonic Foods Added As Such:

            As stated above, there are various types and formats of planktonic foods that can be manually or automatedly added to your systems. Some of the foods available are highly palatable and nutritious. All these varieties and means of delivery have their potential downsides and limitations. Gear can/does fail at times, the foods run out, and there is something to be said re the periodicity of such feeders. Happily there is one great alternative to engage: the use of refugiums.


Foods by ‘Fuge:  Using Ancillary Live Sumps to Produce and Deliver Live Foods for Captive Marine Systems

Of all the several important uses of refugiums, those tied-in life-holding sumps used by reef et al. aquarists, is the production of both phyto- and zoo-plankton. I want to be clear here re both these; they can be easily produced in sufficient quantities for most all sizes, types of reasonably stocked systems. In particular, as regards phytoplankton, there is no need to supplement with other sources unless your system is over-stocked with life that can and will use such.

Sidebar: “Growing Fish Food in Refugia”


Some Guidelines for Optimizing Refugium Production


Size matters. Your refugium should be as large as possible/practical. There can’t be too big a ‘fuge, but the opposite is not so. Twenty percent of the main/display system is a good minimum for space dedicated for culture.


Choice of substrates & their renewal. Carbonate-based sand of several inches depth, calcium carbonate based live rock (or base), and macro-algae of a good choice (often Chaetomorpha, Gracilaria spp.) should be stocked, and the first two periodically (once a year to start) replenished (as they melt down) with new. Having all these media present will optimize your planktonic production.


Flow rates should be, in a word, “slow”. Three to five times turnover per hour (of the refugium itself) is about right… This gives enough circulation to produce gaseous exchange.


Stocking your refugium: In most cases providing your live rock is robust, you won’t find that you need to add any more life to your refugium. The “critters” in and on the rock will populate the sand substrate and macro-algae. Just the same, some folks prefer to buy a ‘fuge livestock kit’ from commercial sources, or borrow a “scoop” or two of sand from a fellow reefer to start off their biota. Unless there is some pressing reason, other types of life (read this as predators) should be left out of your refugium. Crabs, large shrimps, snails, starfishes, fishes of any kind… will detract from the fuges production and utility.



Almost always there’s sufficient life “recruited” as hitchhikers on live rock to populate a refugium. At right, some very active (as judged by the looseness of the substrate) burrowing Polychaete worms. Their reproductive products and bodies are a major source of nutrition in the wild and captive systems.



About Light/Lighting: Providing low illumination (fluorescents of any kind are fine) on a reverse photoperiod w/ your main display system (off when it’s are on and vice versa) is important to not only growing photosynthetic life, providing food chain completeness, but also for timing the release of much of the life to be swept into the display/main tank during its light-cycle… Most all plankton et. Al biotic activity occurs during the night/dark cycle… And this is when your fishes are active in their light-cycle…



Refugiums need light… for all kinds of photosynthetic life (Mangroves at right at friend Dick Perrin’s “Tropicorium”) as well as for your viewing and working about your mechanicals and controllers. Simple fluorescents will do, set on a reverse daylight photoperiod, alternating and possibly overlapping some “day time” w/ your main/display tank’s lighting.



Feeding Your Refugium: Most aquarists eschew purposely putting foods into their refugia, counting on spill-over from the main system and primary production via photosynthesis in situ.; but I encourage you to introduce at least a bit of dried food (sinking pellets are my preference) on a daily basis.






Refugiums need not be expensive or difficult to fabricate. Here is a favorite set up using a Rubbermaid Brute trash can and a simple industrial “pinch clamp” light fixture and flood lamp under an earnest hobbyist’s display in Sacramento, CA.

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A brief personal history of marine aquarium keeping, leading to refugium use: 
An attempt to convince you of the veracity of my opinions and urgings here.

The mid 1960’s: Lollipop/Earl Kennedy, a marine livestock wholesaler in the Philippines. We used raw natural seawater, and lots of it; in the beach location, actually scooped up in buckets, and poured into one end of tanks, overflowing eventually back into the bay/sea. Additionally, screens (hung over the boat side) were employed to sieve out, collect plankton which was used to feed captive stocks.

In the latter 1960’s, working as a retail clerk at Polka Dot Nursery & Aquarium in San Diego, California. Tru-Vu/Aquaplex was in its infancy, selling acrylic aquariums, and we had two for marines, and Sander’s protein skimmers on them. Selling such skimmers/foam fractionators was difficult… hard to convince customers of new technology, especially w/ competitors decrying their use as unnecessary, even deleterious.

Ozone/Ozonizers… RedOx… a further “hard sell” through the 1970’s to date, though tried and true filtration value, in-use in almost all public aquariums, aquaculture facilities.

Andy Eyas of International Seaboard introduced George Smit and the Mini-Reef not-so revolution in the mid 1980’s… We should give credit where credit is deserved; the original glass sumps had a crushed coral area for fostering life as well as denitrification. Because of too-easy breakage, and weight/shipping considerations, these “wet-dry” units were quickly switched to acrylic manufacture and the use of other less-suitable media.

David Boruchowitz, editor of TFH allows me to write a one-pager re Refugiums ’95. Though sumps, with and w/o live components have been around ever since when, this piece marks one of the earlier documented efforts at their popularization.

Back in 2003, friends Steven Pro and Anthony Calfo and I set out to popularize refugium use, and “massage” marine aquarists into easier success with the release of the first book in the Natural Reef Aquarium series, “Reef Invertebrates”. The first hundred or so pages dedicated to design and use of refugiums.


Some Pertinent Notes re Refugiums:

A lesson in productivity: Manta dives in Kona, HI. I’d like to relate an object lesson that demonstrates the capacity for refugiums to produce foods vis a vis a similar situation in the wild. On the “Big Island” of Hawai’i on the west coast lies the town of (Kailua) Kona, with a myriad of dive opportunities. One “stock experience” is the Manta feeding off the Keohole Airport… with divers heading out during later afternoon, doing a getting-acquainted dive, and waiting out the intervening surface interval to rest and blow off nitrogen while others secure lighting on the bottom. There are three permanent anchor/buoys with sometimes more than one boat tied to each, almost every night here. As the sun goes down, the divers get situated setting on the bottom around the lights, and often a sea swirl of planktonic life about them… principally Polychaete worms and crustaceans… much of plankton is “positively phototactic” attracted toward light… In due course, usually a dozen or more “resident” Manta rays, and at times a trans-oceanic specimen or two of much greater size, swoop in repeatedly to scoop up this bounty as food. Now, think on this; there are actually tons of mass in these rays, going to the SAME area night after night, with this patch of sand and rock producing at least tens of pounds of food daily… Amazing? Yes.

            Similarly, though your refugium substrate may seem puny, there is considerable live foods production available on a continuous basis.


About Getting Twisted in the Pumping Process:

            Some refugium-users have expressed concern re biota getting mangled going through the pump on its way to their main displays… Not to worry. Most all arrives intact (enough) to stay alive, serve as food. For folks who still worry, there is the possibility of locating your sump/refugium at the level or above the main display, using the gravity overflow to deliver water from the refugium, pumping to it from the main/display tank.

About Skimmers & Plankton Removal:

            Efficient skimming can remove a good deal of smaller plankton, particularly phyto-. To those with big skimmers, I suggest you run them on a punctuated basis… a few hours on, a few hours off, or do what you can to discharge water from the refugium distal to the pick-up of the skimmer itself.



            The use of live planktonic foods is of tremendous benefit in providing nutrition, exercise and overall health to captive marine systems. Amongst other means, the ongoing production and delivery of such foods through refugiums is the best method available; being consistently dependable, of moderate cost, and providing a few other substantive advantages. All display systems can be improved via the use of said “live sumps” incorporating deep sand beds, live rock, macro-algae culture and reverse daylight photoperiodicity.

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