This article originally appeared in SeaScopeTM, Volume 11, Summer 1994, Aquarium Systems, copyright 1994. All rights reserved by Aquarium Systems, Mentor, Ohio. Permission to reproduce is granted by the publisher to The Breeder's Registry and is not transferrable.
by Cecilia M. Riley
University of Texas Marine Science Institute
There is an expanding interest in breeding techniques for certain high value fish and invertebrates. The pressures on natural populations of coral reef animals and their increasing popularity in the aquarium trade have contributed to this interest. We have worked with many types of fish at the University of Texas Marine Science Institute, but one of our first successes with invertebrates was the cultivation of peppermint shrimp.
The peppermint shrimp (Lysmata wurdemanni) is a Caridean shrimp in the family Hippolytidae occurring from New Jersey through the Gulf of Mexico and the Caribbean to Brazil (Williams 1984). This popular ornamental shrimp is associated with hard coastal substrata such as rock jetties and outcroppings, piers and buoys, and with tubular sponges, especially of the genus Aplysina (Sefton and Webster 1986).
Collection and Maintenance
Adult peppermint shrimp were collected in shallow water from the Port Aransas jetties and maintained in our laboratory at The University of Texas Marine Science Institute. We have found adults to be most abundant in June or July when water temperatures are 25-30°C (72-86°F). They are easily collected after dark using a flashlight and dip nets. Once in the laboratory, adults are kept in 20 gallon aquariums, with standard undergravel filtration, a few rocks, and a lush growth of the marine algae Caulerpa sp. Adult females approximately 5 centimeters (cm) long and the smaller males 4 cm long are housed together with 15-20 in each 20 gallon tank. Adults are fed once or twice daily with chopped raw bait shrimp or fish, and a tropical fish diet prepared in our laboratory.
Egg Production
Adult peppermint shrimp (Lysmata wurdemanni) with clutch of eggs. (Photo by: Cecilia Riley) |
Adults are reproductive year-round with egg production every 10-12 days. They are fed frequently. The water is maintained at 20-30°C (67-86°F) with a salinity of 33-37 parts per thousand (specific gravity of 1.0244 to 1.0275). They are on a cycle of 12 hours daylight and 12 hours dark. The bright green eggs are easily visible through the carapace (shell) and mature in 9-11 days while still attached to the pleopods (rear appendages) of females. Clutch size has varied from 579 to 1707 eggs at each spawning event. When the eggs are mature they become a light tan color, at which time females are moved to larval rearing chambers to spawn. Egg hatching occurs after dark. The next morning the adult is returned to the broodstock aquarium where she will molt and repeat the cycle of reproduction.
Over the course of our work an interesting observation was made concerning the reproductive biology of this species. After the first spawning/molting event several females were isolated from the community tank that contained both sexes. These female shrimp, in the absence of males, then produced at least three additional clutches of fertilized eggs.
Production of eggs by isolated females suggests three possible reproductive strategies for L. wurdemanni. One plausible explanation would be the ability of females to store sperm, a method also employed by other non-Caridean shrimp. Two other possibilities include simultaneous hermaphrodism, where two individuals take turns acting as male and female, each producing the gametes of both; or instantaneous hermaphrodism, the production of male and female gametes by an individual that self-fertilizes. We hope to obtain the answer to this puzzle in our continued study of this species.
Larval Development
The larvae of the peppermint shrimp go through seven major stages prior to metamorphosis into postlarvae (PL). These stages are determined by differences in the development of the major appendages, antennae, rostrum, and tail fan and have been described in detail by Crompton(1992). At hatching the larvae are approximately 2.2 millimeters (mm) long, and within days develop large compound eyes extended on stalks, and the largest pleopod (leg) becomes elongate and paddle shaped. After the final molt, to PL, the compound eyes are on the head rather than stalked, and the paddle-like appendages form the front claws typical of adult shrimp. At this time the shrimp are no longer pelagic (floating suspended in the water column) but instead settle on the bottom and sides of the rearing chambers. This new controlled mobility aids in the switch-over to larger, more diverse foods and increases the animals' feeding ability.
Larval Rearing
When hatched, larvae float in the water column and are such poor swimmers they would be easily sucked down into undergravel filters or damaged by the bubbles of airstones. To avoid physical damage, our larvae are reared in 20 liter round PVC rearing chambers 30 cm in diameter with 150 micron mesh windows on the sides and bottoms to retain larvae and their food in a calm environment. Up to four of these rearing chambers are placed inside a well aerated 400 liter circular fiberglass tank with an external biofilter. An entire clutch is reared together at relatively high densities (40-60 larvae/liter).
Not all individuals of a single clutch mature at the same time. Metamorphosis occurs intermittently from 40 days to 65 days after hatching, by which time all individuals have completed this final larval molt. Our two most recent attempts yielded a 22% survival rate to metamorphosis. After metamorphosis, the young shrimp are moved immediately for maturation into small aquariums with undergravel filtration. Few if any young shrimp are lost after this stage.
From the first day of hatching to six days posthatch larval shrimp are fed newly hatched brine shrimp nauplii less than 6 hours old. These larvae feed at the surface in a strange upside-down manner because their mouths are located on their ventral surfaces. Older larval shrimp are fed progressively larger brine shrimp that have been enriched with algae (Isochrysis galbana, Nannochloropsis oculata) and Super Selco, a food manufactured by Artemia Systems N.V. After metamorphosis, the diet of young shrimp mirrors that of the adults, consisting of finely minced bait shrimp and fish. At this point young shrimp are quite adept at foraging on just about any size or type of particle and will feed on a variety of commercially prepared tropical fish pellets and flakes.
We hope that this information will lend encouragement to the growing number of amateur and professional aquarists to continue captive production of reef animals, despite the many difficulties we have all shared in this field.
Literature Cited
Crompton, W.D. 1992. Laboratory culture and larval development of the peppermint shrimp, Lysmata wurdemanni Gibbes (Caridea: Hippolytidae). Unpublished Masters Thesis, Corpus Christi State University, Corpus Christi, TX.
Sefton, N. and S.K. Webster. 1986. Caribbean reef invertebrates. Sea Challengers, Monterey, CA.
Editor's Note: Ms. Riley will speak at MACNA VI, October 15 and 16, 1994 in Cleveland, Ohio, on the topic of cultivation of marine ornamentals.