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Survival and growth of postlarvae (PL) of Macrobrachium rosenbergii (De Man 1879) were investigated under different alkalinity (25 to 500 mg·L − 1 and total hardness (25 to 1000 mg·L − 1 ). 45 days old PL feed with a rich protein diet (38%) comprising mussels, green beans and commercial shrimp pellets, where individually held in deionised water flow through systems with chemicals added according to the HMSO (1969) formula to make up the required calcium and carbonate concentrations. Increasing alkalinity reduced the growth rate and survival of PL of M. rosenbergii . An alkalinity concentration of 250 mg·L − 1 or above was lethal for PL of the species as total harness increased. Total hardness as high as 1000 mg·L − 1 however, did not have a significant effect in the growth rate or survival as long as the alkalinity was 100 mg·L − 1 or lower. Thus suggesting that water with high hardness and low alkalinity in different countries could be used for the production of the species. Statement of relevance Water suitability for the production of freshwater prawn Calcareous exoskeleton in crustaceans provides protection and support, but also imposes severe limitations, since growth is only possible by moulting. Total hardness and alkalinity of the water are important considerations in the culture of Macrobrachium rosenbergii , since they represent the concentrations of cations (calcium-magnesium) and anions (carbonates), necessary for the mineralization of the exoskeleton. M. rosenbergii has a wide range of tolerance to most of the critical parameters in aquaculture. However, the optimum levels of combinations of both alkalinity and total hardness factors for the species are yet to be fully identified. Therefore, the chemical composition of the different water bodies, and their variations, demonstrate that site selection is of paramount importance for the culture of crustaceans, depending on their requirements for alkalinity and total hardness, and the aim of this study was to investigate the effects of environmental alkalinity and total hardness in the development of PL of M. rosenbergii , as well as to identify the maximum tolerance limits and the optimum range of levels of both factors, individually and as a synergistic effect for the prawns. It was found that alkalinity levels of 250 mg L − 1 as CaCO 3 were lethal for the species and that PL of the species could grow and survive at total hardness levels of 1000 mg L − 1 as CaCO 3 as long as the alkalinity was lower than 100 mg L − 1 as CaCO 3 . [ABSTRACT FROM AUTHOR]

The African River prawnMacrobrachium vollenhoveniiis the largest of the local Palaemonidae prawns along the Cameroonian coast and an important target species for fisheries and aquaculture. A preliminary study on larviculture of this species was carried out at the IRAD-AQUASOL hatchery in Kribi, Cameroon. Berried femalesM. vollenhoveniiwere obtained from the Lobe and Lokoundje Rivers in the Southern Region, typical Lower Guinea rainforest streams. The larval rearing system consisted of a single recirculation system of four 65 L cylindrical plastic containers connected to a submerged biological filter container (65 L). Experiments were conducted three times in the same condition, with two batches of larvae reared separately in duplicate per experiment, at a density of 40/L, temperature 26°C, and salinity 16%. Larvae were fed from 1 day after hatching until metamorphosis to postlarvae (PL) with newly hatchedArtemia nauplii, three times daily at the rate of 5 nauplii per mL water. The number of newly hatched larvae per female body weight unit was not affected by the female size and ranged between 531 to 1349 larvae g−1. The six batches succeeded from hatching to metamorphosis, and the 11 distinct larval stages described forM. rosenbergiiwere found. Larvae in all the batches developed more or less at the same pace up to stage V. However, a clear difference in the timing of appearance of the developmental stages was observed between batches and individuals of the same batch during the subsequent stages. The transition from stage V to stage VI and from stage IX to stage X was longer than the passage to other stages and seems to be the critical rearing period ofM. vollenhovenii. From day 20 onward to sampling, the larval stage index (LSI) showed that larval development of the batch 1 was significantly faster than for all other batches. The time for first appearance of postlarvae was variable between batches (41–74 days), and batch 1 larvae passed through metamorphosis within a shorter span of time (41 days). Survival up to postlarvae was variable among batches, ranging between 3%–9%, and was better in batch 1 (9.31 ± 1.09). The general poor performance in terms of survival and metamorphosis rates of larvae seems to be related to the wild condition of broodstock. To improve performance of larvae, domestication of stock may be necessary. This result is the first recorded success in larviculture ofM. vollenhoveniiin Cameroon. [ABSTRACT FROM AUTHOR]

The livelihoods of a large number of farmers are associated with freshwater prawn (Macrobrachium rosenbergii) farming in gher (modified rice fields with high, broad peripheral dikes) systems in southwest Bangladesh. Most farmers integrated prawn with fish and rice in their gher and followed extensive methods using low inputs. Although farmers have improved their social and economic conditions through prawn farming, constraints include high production costs, low supply of wild fry and snail meat as prawn feed, lack of technical knowledge of farmers, and negative environmental impacts. [ABSTRACT FROM AUTHOR]

Forty post-larval giant freshwater prawns (Macrobrachium rosenbergii) were weighed, measured, marked and placed in groups of 4. Social interactions were screened daily, moults were recorded and the nature and stability of dominance interactions characterised. Half of the prawns were screened for resting oxygen consumption before group formation. In most groups, one or two individuals ('dominants') consistently won the majority of interactions in which they were involved, while others (`subordinates') consistently lost; the remainder were classified as of intermediate social status. Prawns lost more fights on the day before a moult, but despite this, rank was retained after moults. Neither initial size nor growth rates varied with status, but prawns that became dominant had significantly higher resting metabolic rates before group formation than those that became subordinate. Thus in M. rosenbergii the outcome of aggressive interactions can be predicted from the metabolic physiology of the animals although whether the relationship is causal remains to be determined. [ABSTRACT FROM AUTHOR]