Complete Larval Development of the Palaemonid Shrimp Macrobrachium Carcinus (L.), Reared in the Laboratory (Decapoda, Palaemonidae) by P
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COMPLETE LARVAL DEVELOPMENT OF THE PALAEMONID SHRIMP MACROBRACHIUM CARCINUS (L.), REARED IN THE LABORATORY (DECAPODA, PALAEMONIDAE) BY P. C. CHOUDHURY Zoology Department, University of the West Indies, Kingston, Jamaica INTRODUCTION Twenty six species of the palaemonid genus Macrobrachium are known from America and the West Indies. Macrobrachium carcinus (L. ) is a shrimp which lives in fresh and brackish waters of eastern America from Florida to Southern Brazil and in the West Indies. These shrimps are very large and specimens of 23 cm long have been recorded by Holthuis (1952). In Jamaica M. carcinus lives in fresh water rivers and streams where they are not very common and are caught occasionally during the rainy season only. Lewis & Ward (1965) have described the developmental stages of this species. They have described only the external morphology of the larval stages. The larval stages described by them were based on the age of the larvae in days rather than on morphological changes in the larvae during development. Lewis (1961) has given a preliminary account of attempts to rear M. carcinus. Lewis et al. (1966) have reported a study on the breeding cycle, growth and food of M. carcinus. Ingle & Eldred (1960) have noted its potential as a shrimp suitable for artificial cultivation. Mercado (1959) reported his plan for artificial culture of this species in Mexico, but no further information is yet available on this plan. M. acanthurus (Wiegmann) is the only other species of this genus in the western hemisphere whose complete larval development has been reported on (Choudhury, 1970). Ling & Merican (1961) have described the developmental stages of larvae of the eastern species, M. l'osenbel'gii (De Man). The purpose of this present paper is to give an account of the complete larval development of M. carcinu.r, the larvae of which were reared in the laboratory from hatching through all stages until metamorphosis to juveniles. MATERIALSAND METHODS Berried females were caught in the Black River, in the Parish of St. Elizabeth, Jamaica, and were transported to Kingston in large plastic containers with strong constant aeration. Only one berried female was kept in each aquarium (60 cm X 30 cm X 30 cm) containing fresh water. The animals were under constant aeration and were fed with chopped fish only once a day. Unused food and faecal materials were siphoned out once a day. 52 Hatching always took place during the early hours of night. The newly hatched larvae were induced to concentrate at one corner of the aquarium by focusing a light on that corner and shading the rest of the aquarium with black paper. The larvae were then siphoned out and kept in clean fresh water overnight. The fol- lowing morning the larvae were slowly acclimatized to salinity 140/0o to 160/00 contained in aquaria (40 cm X 30 cm X 30 cm), in which they were reared through all stages until metamorphosis to juveniles. Larvae reared in salinities higher or lower than 140/00 to 160/0o failed to survive until metamorphosis. All larvae were under continuous moderate aeration supplied from an air compressor. The larvae were fed on nauplii of Artemicc salina (L.) and particles of food prepared from fish and crustacean muscles by the method described by Ling (1961). Unused food particles, exuviae, dead larvae, larval faecal matters and dead Artemia salina were siphoned out twice a day. It was not possible to control temperature and this varied from 24°C to 28°C; pH of the water was checked every alternate day and was found to vary from 7.0 to 8.5. All illustrations were made with the help of a camera lucida mounted on a binocular compound microscope. Notes on chromatophores and other detailed characters were made from live or freshly killed larvae. Measurements were made with an ocular micrometer. Total length of the larvae was measured from the tip of the rostrum to the posterior edge of the telson without setae. DEVELOPMENTOF LARVALSTAGES From the time of hatching until metamorphosis into juveniles, twelve distinct larval stages have been discovered, detailed morphological descriptions of which are given below. Development of larvae was very regular until stage VI. From the time of hatching until stage VI each moult resulted in a new larval stage. Thereafter larval development became irregular and every moult did not give rise to a new larval stage. Sometimes moulting took place without any morphological change, or with insufficient morphological changes resulting in production of larvae of intermediate stage. Larvae metamorphosed to juveniles in a minimum of 56 and a maximum of 66 days from the time of hatching. First Larval Stage (figs. 1, 2). Age: 1-3 days from hatching. Length: 2.0-2.1 mm (from tip of rostrum to tip of telson, excluding setae). Body slightly bent on abdominal segment 3. The larvae are more or less transpa- rent except for a few localized chromatophores and pigment. Distribution of chromatophores and pigment is as follows: one small red chromatophore on the outer corner of the distal end of the antennular peduncle; one small red on either side of the base of the rostrum; one large dark red with dendrites on the junction of the eyes with the carapace; two pairs of bright red with long dendrites on the dorsal side of the abdominal segment 3; one small red on the region of the anus; one small red on the inner ramus of both the biramous buds of pereiopods 1 and .