THE LARVAL HATCH FECUNDITY OF A STOCK OF THE GIANT FRESH WATER PRAWN Macrobrachium rosenbergii By. George B. Brooks, Jr. Ph.D. Environmental Coordinator/Aquatic Scientist Gila River Indian Community Adjunct Assistant Professor Wildlife and Fisheries Resources University of Arizona, Tucson

Introduction n n With few major Macrobrachium hatcheries in the continental U.S., shortages of available seed could occur if there were a sudden increase in demand for postlarvae. n n Therefore to support a viable local prawn industry, local seed sources (hatcheries) must be developed. n n Successful hatchery management requires a knowledge of the number of brood stock required to produce a defined number of postlarvae.

Larval Hatch Fecundity (LHF) n n In Macrobrachium rosenbergii, fecundity is a function of body weight. Larval Hatch Fecundity (LHF) is defined as the number of larvae released from the egg mass following incubation (Malecha 1983). n n The literature reports two average LHF values for M. rosenbergii. – –1,000 larvae per gram (New and Singholka (1982) and D’Abramo et al 1995) – –405 larvae per gram (Malecha 1983)

Purpose of Study n n The purpose of this study is to determine the larval hatch fecundity of one stock of M. rosenbergii available in the United States in comparison to reported LHF values.

Materials and Methods n n In March of 1998, 6 females with dark near ripe eggs, were captured as part of periodic sampling from an Arizona fish farm were, weighed and individually isolated in 37 liter (10 gallon) tanks until their eggs hatched. The newly hatched larvae were counted volumetrically (New 1990).

Materials and Methods Cont. n n Larval Hatch Fecundity is the number of larvae hatched, divided by the after hatching mass of the female M. rosenbergii as measured in grams (Malecha 1983). The LHF value for this stock of prawns was defined as the average of the individual LHF values from the reproductive females.

Results Figure 1. Average # of Larvae produced per gram of female weight

Discussion n n As seen in Figure 1, The average number of viable larvae per female was 430 per gram of body weight gram. Though preliminary, these results suggest the LHF value is far nearer the 405 larvae/g value than the 1,000. n n Possible Reasons for the differences: – –Stocks within the native range for the species (Anuenue (Hawaii), Australian A, Australian B, and Palau. demonstrate differences in larval development rate (Malecha 1983, Sandifer and Smith 1985). This suggests the possibility of genetic divergence. Genetic divergence could also be responsible for differences in LHF. – –The literature and communications with prawn producers suggest the parental prawns used in this study probably originated with Anuenue stock from Hawaii, the same stock used by Malecha (Malecha 1983, Sandifer and Smith, 1985, Craig Upstrom, owner Aquaculture of Texas, Personal Communication). Origination from the same stock could in part account for the similarities in LHF.

Discussion (Cont.) n n An additional possibility accounting for differences and similarities in LHF are regional culture conditions. Growth rates, survival and other biological factors can be affected by how the animals are cultured. Placing genetically similar animals under similar conditions may produce similar results. If the growout conditions and spawning conditions provided by Malecha (1983) were similar to those in this study, then similar results could be expected.

Literature Cited n n D’Abramo, L. R., Daniels, W. H., Fondren, M. W. and M. W. Brunson Management practices for culture of freshwater prawn (Macrobrachium rosenbergii) in temperate climates. Mississippi Agricultural and Forestry Experiment Station Bulletin September. 12pp n n Malecha, S Commercial seed production of the freshwater prawn, Macrobrachium rosenbergii, in Hawaii.Pages in: J.P. McVey eds, CRC Handbook of Mariculture, Vol.I, Crustacean Aquaculture. CRC Press, Inc., Boca Raton, FL. n n New, M.B. and S. Singholka Freshwater prawn farming. A manual for the culture of Macrobrachium rosenbergii. FAO Fisheries Technical Paper No.225. Sandifer, P.A., and T. I. J. Smith Freshwater prawns. Pages in: J. V. Huner and E.E. Brown eds: Crustacean and mollusk aquaculture in the United States. AVI Publishing Company Inc. Westport, Connecticut.