Feature Article: Behavior And Breeding Of Peppermint Shrimp
As a reefkeeping enthusiast I have delighted in coral propagation for the last several years and my hobby led me to become Invertebrate Director at our city's largest aquarium store. There I have had a chance to enrich my hobby in many ways. Surrounded by an array of aquarium products, livestock, and literature I have been able to move on to the "next level" of aquaculture, breeding a true marine ornamental, the familiar Peppermint Shrimp. Thanks to a particularly inspiring article by Matthew Wittenrich in the summer 2002 Seascope newsletter profiling his successes breeding these shrimp, I decided that this was something I had to try. One of the challenges I've faced being in charge of the shrimp we sell at the store is understanding their behavioral interactions and this experience has given me a keener understanding of how to keep and breed these fascinating arthropods.
In this article I hope to not only add to the present body of literature on the topic of peppermint and Lysmata shrimp breeding in general but to focus a greater emphasis on behavioral interactions of the shrimp communities in broodstock and growout scenarios. Also I will explain some unique techniques I've developed that have contributed to my success.
I began my project last year by creating a 55 gallon broodstock tank for the adult shrimp and placed as many as 28 individuals in there at first. I was not surprised to witness progressive cannibalism amongst them over time which has confirmed my strong belief that you can only house just so many shrimp within a given amount of tank space. Today my conclusion drawn from this is that just under ten adult peppermint shrimp can be successfully housed in a tank of this size. It is during molting episodes when cannibalism most often occurs and this is also when mating occurs as well so there seems to be a fine line between sex and murder in the shrimp world depending on the density of individuals in a given captive environment. Naturally hunger is also a strong factor and underfed shrimps are certainly more prone to cannibalistic behavior. Feeding the adult shrimps daily with quality feeds, vitamin and lipid enriched, is a big part of success with large hatches and healthy larvae.
Perhaps the most fascinating thing I've been able to witness is the actual reproductive process in front of my eyes at night in the tank. Since there are no other fish or organisms of any kind in the broodstock tank the shrimp are free to exhibit uninhibited sexual behavior without fear of predation. When an adult starts to hatch larvae from the swollen mature eggs attached to its pleopods (swimmerets), it is chased around the tank by the other shrimp no doubt in hopes of capturing a tasty larval meal as well as the phenomenal attraction of mating with that shrimp after its subsequent molt. All the shrimp exhibit a very high activity level, swimming in a racetrack manner around the tank. Once hatching is complete the "mother" shrimp will exit its exoskeleton even as another shrimp is right on top of it waiting for its chance to mate by grabbing the soft-bodied "female phase" shrimp and contacting it crossways from underneath. As simultaneous hermaphrodites, these very same two shrimp may have their male/female roles reversed within so many days to a week as the eggs reach maturity on the adult that had previously enacted the fertilizing male role!
Exciting as all this was, only until I could isolate the larvae, known as zoeae by biologists, would I really be in business to raise them. Inevitably after such evenings of observation it became obvious when a hatch was imminent or in progress. I managed to collect my first batches of larvae by the simple, albeit tedious method of cutting off all pumps in the tank and concentrating them at a spot under a light to which their phototrophic nature attracted them and then dipping them out with a cup to transfer to their larval rearing tank. It became quite apparent that a more efficient method of larval collection would be necessary so I constructed a device for this purpose designed after Joyce Wilkerson's "Larval Snagger" detailed in her book on raising clownfish. Another book I was reading at this time, "How to Raise and Train Your Peppermint Shrimp" by April Kirkendoll. It described the use of a larval collection device as well. This acrylic box sprouting siphon tubes, a fine mesh strainer, a small powerhead, and a nightlight for larval attraction seemed bizarre if not questionable for the purpose it was intended. When even after the very first night it was installed I discovered it full of tiny zoeae, I was overjoyed and have come to firmly believe in the need to employ a larval collection device if one is going to regularly raise these shrimp. Although the Wittenrich article describes an alternate method of adult transfer to a rearing tank for larval collection, I tend to agree more with Kirkendoll's recommendation of broodstock tank larval collection to minimize undue stress to the adult and frankly it seems far more practical than trying to capture a specific adult from the main tank.
A tall, bare 15 gallon tank wrapped in black plastic trash bag material (to shield it from side lighting) filled with saltwater and an air stone serves as the larval tank. At first I created a siphon design to transfer water to and from the broodstock tank in hopes that the biological stability of the adults' system would prevent ammonia and nitrite from poisoning the larvae. A fine mesh strainer kept the larvae from being siphoned back through. Well intentioned as this may have been, this piggy-backing system design turned out to be deadly to my adults as the heavy feeding of the larval tank polluted the broodstock tank so much that I ended up losing all my adults to disease! This was my first major setback, but nevertheless I successfully managed to bring 76 larval shrimp to metamorphosis in this first trial. I now follow the so- called hobbyist method of larval tank rearing as advocated by both Wilkerson and Kirkendoll where the larval tank is an independent entity receiving daily bottom siphonings and water change to insure water quality. In the future I plan to design a dedicated larval filtration system to enhance their life support and environmental stability. I also would like to design a multi-tank larval system utilizing the "planktonkreisel" concept of conical larval tanks with upwelling water movement used in advanced aquaculture laboratories.
Whether the larval tank has its own filter or not, frequent bottom siphonings will be necessary especially when dead foods are offered. Cloudy water is also a familiar situation that further indicates need for additional water change. Virtually every single day I am changing some percentage of larval tank water. If ammonia or nitrite is an issue an ammonia detoxifying conditioner can be added.
A battery-powered airpump check valved into the airline will save the lives of larvae if the power goes out. Larvae can only last so long without the gentle rolling of the water that the airlift creates. Without this they will eventually settle to the bottom and die. The type of airpump that automatically kicks on when sensing power loss is the one that is required.
Although for a brief time I was culturing rotifers and phytoplankton in the thought that this would be a necessary part of the process, the Kirkendoll book confirmed that this was not needed and that the zoeae are started on new hatch artemia from day one. That has proven to be a boon as phytoplankton culture seemed particularly tedious and prone to culture crashes. Brine shrimp are easy to hatch but it is important to always have a newly hatched batch of artemia nauplii the morning following a peppermint shrimp hatch. When I am collecting larvae I force myself to start a new hatch of brine shrimp as a daily morning ritual so that the batch from the day before is ready to feed to my shrimp larvae. Brine shrimp nauplii that may be ready for feeding before larvae are obtained can be fed to my reef systems otherwise. Since the peppermint shrimp breed so regularly hatches can be obtained every few days. Collected larvae can be added to the same larval tank for up to a month and although there may be some cannibalism of the smaller younger zoeae, if food items are supplied in daily abundance this doesn't seem to constitute much of a problem.
Kirkendoll's recommendation of a fine bubble diffuser in the corner of the tank works well for my larvae and I use a limewood air block for that purpose. A gentle air output seems to be best for these little guys which can be increased somewhat as they mature, but not so strong as to batter them against the sides of the tank. One of the great things about peppermint shrimp larvae is their willingness to grab onto and eat various dead foods which are easily offered. During my first batch of larvae that I raised I used as many as three airstones with vigorous output in order to keep certain frozen foods suspended which the larvae did actively feed on but in retrospect this was surely far too turbulent for them. Without this vigorous output the frozen foods just settled on the bottom. I was somewhat disappointed with flakes too. Although they would float for a while which was good they too would eventually sink to the bottom unavailable to the larvae. Then I had an inspiration. Since they obviously enjoyed flake foods and the challenge was to have a continuous presence of such in the tank, why not utilize an automatic flake feeding device as used for freshwater fish? I used a rotary flake feeder that I modified so that every compartment on the dial would dispense flakes continuously all day long into the larval tank. It was a resounding success! The only drawback to this was the absolute necessity of a nightly bottom vacuuming as a thick layer of flakes quickly built up. As long as the nightly siphoning was performed I never had any problems with larvae getting tangled up in it or mortality due to excess pollution.
Ideally the prescribed methodology for the maturation of Lysmata wurdemanni (or L. rathbunae ) zoeae through live foods entails feeding progressively mature artemia as the shrimp larvae mature and that the culturist would have successful artemia cultures in growout for this purpose. Good as this would be, it's not a necessity either especially if you are feeding other foodstuffs as described above. I feed new hatch artemia daily for the first four weeks (or longer if there are new larvae still being added to the tank) in combination with the flakes. After the fourth week the zoeae are usually big enough to handle adult brine shrimp which then can be offered. Raising brine shrimp to adulthood is a challenge even for advanced aquarists due to the fouling of culture water and I must admit that this has still proven to be a stumbling block. Fortunately, working at an aquarium store where live adult brine shrimp are available every week has simplified this issue for me. When the peppermint larvae are old enough for adult brine I just switch them over to that while feeding the flakes all along and they do just fine with that. Having access to live adult brine shrimp is obviously going to be a big advantage if one is trying to raise peppermint shrimp. The adult brine should be fortified with HUFA-enriched feeds and phytoplankton.
The larval tank should be shielded with dark or black material throughout the shrimps' larval stages, but it is okay to pull the front cover aside for temporary viewing. Biofilms will noticeably build up on the front glass after a week and zoeae can become coated in this material as they swim against the front glass due to side lighting while viewing. A quick easy cleaning of the front glass with an algae magnet I have found to be a great way to improve visibility as well as minimize biofilms that can coat and harm larvae during viewing. Algal growths of any length should also be scraped off the sides of the tank to keep newly hatched larvae from getting tangled.
Typically my shrimp larvae will metamorphose (the final of many series of molts) into tiny little shrimp along the sides of the tank after their fifth week. I wait until all the shrimp have metamorphosed before they are transferred to their growout environment. Removing post larval shrimp will be problematic if there are still zoeal stage larvae floating around the tank.
Here I assert the importance of a dedicated site for growout of the shrimp. All the work put into raising the larvae will surely be for nothing if they are added too soon to a typical aquarium. Often they will just disappear never to be seen again. This I learned the hard way. Also you cannot expect to house fifty of them in a ten gallon tank either as the same issues with cannibalism will be played out until you are down to your last shrimp! I toyed with different ideas of keeping each shrimp in a separate cubicle but this wasn't very practical. I ended up creating an array of growout troughs, shallow plastic trays with plenty of space which were plumbed in line to a reef system and became a baby shrimp sanctuary. I collected rocks from the side of the road and laid these and numerous lengths of scrap vinyl hoses around in the troughs for the little shrimp to hide in and it has worked out very well. They just need a dedicated space of sufficient size proportions to allow them to grow to a marketable size to go into a regular aquarium. These subadult juveniles need to be fed every day to optimize growth and deter cannibalism.
The 2nd batch of shrimp I raised in 2003 occurred in the fall when I had a new population of adults and had perfected a more streamlined system of brine culture, larval collection, and better larval survival with the auto feeder. With this batch I brought a sizeable 220 shrimp to metamorphosis.
Another experiment I tried involved adding 11 juvenile shrimp back into the adult broodstock tank to see how they would interact. At first they coexisted in seemingly peaceful groups but after a few weeks it became apparent that the larger adult shrimp were attacking the younger juveniles, a spectacle I bore witness to during a night viewing session. Eventually all the juveniles disappeared. The lesson one can draw from this is the need for shrimp communities to be composed of individuals of comparable size for optimum survivability.
The raising of these shrimp over the past year has simply been one of the most rewarding things I have ever done. As each component in the process developed the excitement heightened until ultimate success and the creation of a systematic methodology became reality. Now I am looking forward to future attempts at other marine ornamental species.
- Kirkendoll, April, 2001. How to Raise and Train Your Peppermint Shrimp.
- Riley, C.M., 1994. Captive Spawning and Rearing of the Peppermint Shrimp (Lysmata wurdemanni). Seascope, Summer.
- Wittenrich, Matthew, 2002. Metamorphosis in 19 Days (Breeding Lysmata rathbunae Shrimp). Seascope, Summer.
- Wilkerson, Joyce D., 2001. Clownfishes (A Guide to Their Captive Care, Breeding & Natural History).