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Unialgnl additions in various concentrations were used to evaluate algal supplements in both static and recirculating water system larviculture of Macrobrachium rosenbergii. Larvae were reared in 60 liter, black fiberglass, rounded bottom tanks at stocking densities ranging from 50 to 75 larvae/l. Cultures were maintained at 12 ppt synthetic seawater at 28 ± 1°C with constant light and moderate aeration. Artemia salina nauplii were used as the primary ration and fed at concentrations of 10 to 15 nauplii/ml. Fish roe (Mugil sp. and Cynoscion sp.) were used as secondary rations after day 9/10 in all cultures. Results showed that unialgal supplements, particularly those of the Chrysophyta (i.e. Isochrysis galbana, Pseudoisochrysis paradoxa, and Phaeodactylum tricornutum), significantly increased survival of larvae and production of postlarvae in both static and recirculating water systems. Mean survival was highest in recirculating algal‐supplemented cultures (82.7%) and static algal‐supplemented cultures (78.8%) and lowest in recirculating and static control cultures (50.9 and 57.0%, respectively). Post‐larval production averaged 59/1 (78% of the stocking density) in recirculating and 47/1 (74% of the stocking density) in static P. tricornutm supplemented cultures while static and recirculating controls averaged 20/1 (39%) and 32/1 (41%) respectively. Peak production of post‐larvae occurred earlier (day 28) in algal supplemented recirculating cultures than in controls (day 34) indicating that algae may also decrease length of time to metamorphosis. Survival data from all experiments were analyzed by ANOVA with regression and indicated a positive, significant relationship between algal concentration and larval survival. Periodic monitoring of nitrogenous compounds (NH4, NO2, NO3) indicated that these aspects of water quality were not directly related to the enhancement of M. rosenbergii larval culture by algal supplements.

Canadian populations of Mercenaria deserve recognition as stocks distinct from the larger population of the U.S. Atlantic coast. Although the hard clam occupies a virtually continuous range from Florida to Massachusetts, its distribution north of Cape Cod becomes disjunct. Here, we use protein electrophoresis to determine gene frequencies a seven polymorphic enzyme loci in clam populations from Maine, USA, and New Brunswick and Prince Edward Island, Canada, and compare our results with previously published data from Massachusetts. The fit to the Hardy–Weinberg expectation within populations was very good. The Maine population showed small but statistically significant divergence from its putative source population to the south at most loci, with an apparent loss of two rare alleles. Both Canadian populations showed larger levels of divergence, with the loss of 6–12 alleles and significant reductions in overall heterozygosity. The recognition of a St. Lawrence stock of hard clams at Prince Edward Island may have important implications for the fishery.