Search

Macrobrachium vollenhovenii (Herklots, 1857), the largest of the indigenous West African Palaemonidae prawns, has a high potential for aquaculture. This work was carried out to assess the effect of temperature on embryonic development and offspring quality of this species. In the phase one experiment, females at stage V of gonadal development incubated their eggs at three experimental temperatures and their embryonic development was evaluated. Seven embryonic developmental stages were observed: fertilisation, mitosis, morula, blastula, gastrula, nauplius and larvae. The incubation periods were 19, 14 and 13 days at 26 °C, 28 °C and 30 °C, respectively. A temperature of 30 °C resulted in higher broodstock mortality (33.33%). In phase two, larvae were reared at the respective temperatures for 30 days at a stocking density of 30 larvae per litre of water. Offspring quality was significantly different between treatments from day five onwards, with the fastest development at 30 °C followed by 28 °C. However, larval survival rate was significantly higher at 26 °C (31.7%) followed by 28 °C (27.6%). A temperature of 28 °C could therefore be recommended as the most favourable for embryonic development and larviculture of M. vollenhovenii. These findings will help bridge the knowledge gap with respect to captive breeding and hatchery technology for M. vollenhovenii. [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]

Abstract This paper describes the successful use of two tagging systems, both produced by Northwest Marine Technology Inc., on larval and postlarval giant freshwater prawns, Macrobrachium rosenbergii. Visible implant (VI) elastomer tags (a coloured liquid that solidifies under the epidermis) were used on stage XI larval prawns (mean weight 0.01 g) and postlarval prawns (mean weight 0.07 g). VI alphanumeric tags (small biocompatible plastic labels also inserted under the epidermis) were tested on postlarval prawns (from a weight of 0.5 g). Tags were inserted using clove oil as anaesthetic, and survival, mortality and growth rates of tagged animals were compared with those of controls that were handled but not anaesthetized or marked. Twenty per cent of the larval prawns (the smallest of the group) died just after tagging, but thereafter the remaining prawns survived well, as did all the tagged postlarval prawns. Visibility of the VI elastomer tags in larval prawns deteriorated with time, though 79% of marks were still visible to the naked eye 70 days after tagging. VI elastomer tags in the postlarval group remained clearly visible for up to 100 days. Visibility of the VI alphanumeric tags fell shortly after tagging, but remained adequate thereafter. Moult rates in control and tagged animals were the same in larvae with VI elastomer tags and postlarvae with VI alphanumeric tags, but the moult rate in the postlarval prawns given elastomer tags was slower than in controls. Rates of growth were similar in tagged (elastomer and alphanumeric) and control postlarval prawns, once the size-dependent mortality of tagged larval prawns was taken into account. We conclude that VI elastomer tags could be used to mark small numbers of individual larval and immediately postlarval prawns for periods of several months, and that VI alphanumeric tags could be used to mark an unlimited number of individuals from a size of approximately 0.5 g. [ABSTRACT FROM AUTHOR]