The palaemonid shrimp Macrobrachium macrobrachion is widely distributed in coastal rivers, estuaries and inland waters of West Africa. This species is economically important because it is the one of the two main freshwater shrimp commercially exploited by artisanal fisheries in southern Benin, besides showing great potential for aquaculture. Despite this, little is known about its reproductive biology in the natural environment. Considering these facts, the present study aimed to establish some breeding parameters for M. macrobrachion in Benin. Overall, 2424 specimens were collected between May 2015 and October 2016. Monthly changes in gonado-somatic index (GSI) and hepato-somatic index (HSI) suggest that the breeding season runs from July to October. In the Ouémé River Delta, the estimated size at first maturity is 8.16 cm TL in females, while it is 7.47 cm TL in males. In the Mono River/Grand-Popo Lagoon complex, the size at first maturity is 7.27 cm TL in females while it is 6.56 cm TL in males. The structure of the ovary as observed in females from either site just before spawning, shows the presence of two types of oocytes at different sizes and various developmental stages. Analysis of such ovarian structure suggests that M. macrobrachion has a synchronous oogenesis with a breeding season limited to a few months of the year. Fecundity was found to be between 3144 and 26 489 eggs in the Ouémé Delta, while it goes from 3124 to 22 660 eggs in the Mono River/Grand-Popo Lagoon complex. The present study provides important information on the reproductive biology of M. macrobrachion and of freshwater shrimp in general, and can also serve as a significant foundation for the aquaculture of species of freshwater shrimp.

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Knowledge of the diet of Macrobrachium macrobrachion (Herklots, 1851) in its natural environment is a key factor facilitating its successful breeding. We have analysed the stomach content of 452 specimens collected from the Ouémé River Delta (ORD) (338 stomachs) and from the Mono River/Grand-Popo Lagoon complex (MGLC) (114 stomachs), from February to October 2016. The analysis enables to calculate the coefficient of vacuity for the ORD (3.50%) and for the MGLC (3.50%). The results show that M. macrobrachion has a detritivore-omnivore type of diet, feeding mainly on phytoplankton (diatoms and cyanophytes) and detritus. However, the diet of the young shrimps, composed mostly of insect larvae, differs from that of adult. In the adult M. macrobrachion, the pace of feeding activities is greatest in the morning (6.00 to 9.00 am), low in middle of the day (10.00 am to 13.00 pm), and there is a slight trophic activity between 17.00 and 22.00 pm. Outside of the above periods, i.e., from 14.00 to 16.00 pm and 23.00 pm to 5.00 am, the species is at rest. Juveniles feed at dawn. In the nighttime and at dusk, groups of shrimps of varying sizes do feed. The findings of this study suggest that live prey is the best feed for the larvae of M. macrobrachion in captivity and should be distributed preferably early in the morning.

The weight-length relationship and the condition factors are fundamental parameters with several uses in biology, fish ecology and fisheries management. Thus, in the Special Wildlife Reserve of Gueumbeul (SWRG) in Senegal, the weight-length relationship and condition factor were established for Mugil cephalus (Linnaeus 1758). A total of 311 individuals (97 females and 214 males) of M. cephalus were collected by the artisanal fishery using cast nets. The total length and weight ranged from 11.1 to 25 cm and 15.9 to 145.26 g, respectively. The results showed that in the SWRG, both in females (b = 2.60) and males (b = 2.899), M. cephalus had negative allometric growth. The analysis of variance showed no significant difference (p > 0.05) in the coefficients of determination between females (R = 0.96) and males (R = 0.84). Condition factors (K) were 3.07 and 1.23 for males and females respectively for M. cephalus in the reserve.

The freshwater prawn Macrobrachium macrobrachion (Herklots, 1851) is widely exploited in the Oueme Delta and the low Mono in Benin. The structure and population parameters of M. macrobrachion were evaluated to provide accurate scientific information for the better exploitation and rational management of freshwater prawn species in these areas. In Oueme Delta (1928 specimens) and low Mono (1045 specimens), 2973 specimens were sampled by artisanal and experimental fishing and analysed. The prawns were caught between January and December 2016. Total length and total weight were taken from each specimen. Global and monthly size–frequency distributions showed that recruitment in both populations takes place from August to October with a peak in September. The population parameters obtained by analysing frequency data with FiSAT II software (FAO‐ICLARM) showed an L∞ = 15.50 cm, K = 0.35 year−1, t0 = −0.56 year in Oueme Delta and L∞ = 15.30 cm, K = 0.45 year−1, t0 = −0.43 year in low Mono. The growth performance index (Φ′) was 1.93 and 2.02 for the Oueme Delta and low Mono populations, respectively. The exploitation rates (Emax and E0.5) suggest that more than half of the M. macrobrachion population was exploited in the two areas. Natural and fishing mortality rates showed that both populations of M. macrobrachion were vulnerable to natural and fishing death. The estimated first capture size (Lc) revealed that the majority of the two populations of M. macrobrachion were captured before they reached the size at first sexual maturity (L50), reflecting fishing pressure on small individuals and growth overfishing in both areas. These results showed that the used fishing gears and the fishing frequencies in both areas did not allow the majority of the prawn to grow and reproduce at least once before being caught.