FECUNDITY AND FERTILITY OF Macrobrachium amazonicum ( CRUSTACEA , PALAEMONIDAE )

In Brazil, studies with native freshwater prawn species were discontinued due to great importance of Macrobrachium rosenbergii. Therefore, it is necessary to continue investigations about our species, in order to develop technology adequate to our reality and in a future allow prawn farmers to culture other species. The aim of this study was to determine the fecundity and fertility of Macrobrachium amazonicum captured monthly from June 1999 to June 2001 from Jaguaribe River, Itaiçaba, Ceará, Brazil. Prawns were collected using fishing net and transferred at Biological Science Laboratory, Ceará State University (Fortaleza, Ceará, Brazil). Among the ovigerous M. amazonicum females, 60 were randomly selected to determine fecundity. The eggs adhered to the pleopods were taken out and they were then placed in a Gilson solution, and then stored in alcohol 70%. Individual fecundity was determined from the total egg counting, using a stereoscopic microscope. To determine fertility, ovigerous M. amazonicum females were stored in individual 10 L-glass tanks maintained under strong aeration. After the hatching, the larvae were siphoned and counted. The data referring to total length and weight of all the females, storage date, coloration and number of eggs, weight and coloration of gonad and number of hatched larvae were noted. With respect to average fecundity (F) by length classes, the lowest and highest number of eggs observed was 696 and 1,554, respectively. As for fecundity by weight classes, the lowest number of eggs observed was 760 and the highest, 1,690. The highest number of eggs observed individually per hatching was 2,193. Average fecundity/total length (L) and average fecundity/total weight (W) may be expressed by a linear relationship. The adjusted equations are: F = –411.6 + 203.1 L (p < 0.0001) and F = 566.4 + 157.3 W (p < 0.0001), respectively. In the analysis of average fertility (N) per length classes, the lowest and highest number of larvae observed was 374 and 1,301, respectively. With respect to fertility per weight classes, the lowest number of larvae was 581 and the highest, 1,391. In this work, the maximum number of larvae observed per hatching for females kept in laboratory was 2,594. Average fertility/total length and average fertility/total weight may be expressed by a linear relationship. The adjusted equations are: N = –1042.7 + 264.9 L (p < 0.0002); N = 384.1 + 160.3 W (p < 0.003). From these results we can deduced that fecundity and fertility of M. amazonicum are lower than ones commercial species, nevertheless it can be captured during all year long. The number of captured prawns was large in the months whose level of water was low; the inverse was observed in the months that the river was with a high volume of water.


INTRODUCTION
The freshwater prawn farming has already become in the last years a major contributor to global aquaculture, in terms of quantity and value (New, 2000).
Historically the freshwater prawns production was 5% of the whole prawn production in the world (New, 1995).However according to FAO data (2000), cited by Valenti (2002), world production of freshwater prawn between 1990 and 2000 increased from 21,000 to 118,500 tons per year, which corresponds to an increase of about 500%.Although these data refers only to Macrobrachium rosenbergii, the most cultivated species in the world, another two species are becoming increasingly more popular in some Asian countries, M. malcolmsonii in India and M. nipponense in China (Kutty et al., 2000).
An special prawn species is considered economically feasible for farming when it presents some characteristics such as fast growth rate, easy repro-duction in captivity, high fecundity, rusticity, low aggressiveness, resistance to diseases and commercial value (Coelho et al., 1981;Valenti, 1985).
The freshwater prawn farming is simpler than saltwater prawn, with lower costs, since the ponds may be built in small, medium and large size properties, located on the coast or inland (Amaral & Neves, 1989;Valenti, 1990).
Freshwater prawns are decapode crustaceans belonging to the Palaemonidae family.Although they are also called prawns as their saltwater counterparts, they are closer to lobster regarding their evolution, thus presenting many similarities mainly with respect to reproduction habits (Jalihal et al., 1993;Valenti, 1996;Pinheiro & Hebling, 1998;Ismael & New, 2000).The vast majority of freshwater prawn species of commercial interest belong to the Macrobrachium genus is founded in the tropical and subtropical regions of the world (Bowman & Abele, 1982;Chace, 1992).
In Brazil, studies with the three most important indigenous freshwater prawn species M. acanthurus, M. amazonicum and M. carcinus started in the beginning of the 70s, with the objective of developing a farming technology adequate to our reality (Cavalcanti, 1998).However, these investigations were discontinued in 1977 due to import of M. rosenbergii post-larvae, an exotic species with welldeveloped farming techniques throughout the world (Valenti, 1993).Currently, M. rosenbergii is the only freshwater prawn species used in commercial farming, since their biology and farming technology are well known compared to other species (Valenti, 1990).Therefore, it is necessary to continue investigations about occurrence, life cycle, reproduction, growth and habitat of our native species, in order to develop technology adequate to our reality, and in a near future allow prawn farmers to cultivate other species.
From the Brazilian indigenous species, M. amazonicum is currently preferred for farming, due to fast growth and easy maintenance in captivity.Although total growth is less than for M. acanthurus and M. carcinus, the species does not present the aggressiveness characteristic of those, in addition to being more resistant to diseases and predators (Lobão & Rojas, 1991).
M. amazonicum is indigenous in South America, and can be found in several rivers of the continent from Venezuela to Paraguay (Rodriguez, 1980;Romero, 1980;Gamba, 1984).In Brazil, the species can be found in rivers and lakes of the North, Northeast and Midwest, which indicates the species has preference for hot climate regions (Kensley & Walker, 1982;Bialetzki et al., 1997).
The researches about M. amazonicum have been developed in the last years with the involvement of universities, institution of research and agencies of development.In Pará, Brazil, M. amazonicum postlarvae of that species are produced in commercial pounds (Moraes-Riodades & Valenti, 2001).
M. amazonicum was brought from the Amazon basin in the 40s and introduced by the Fishery Service from the Departamento Nacional de Obras Contra as Secas (DNOCS) in several dams of the Northeast as forager species for carnivore fishes (Paiva & Campos, 1995).Due to adaptation and facility to reproduce in confinement, the species disseminated throughout the rivers and lakes of the region, thus becoming an important food source and reaching wide commercialization in the Northeast (Valenti, 1985).
According to Lombardi et al. (1996), in Brazil, population of river banks has subsisted on freshwater prawn fishing either as food or bait used for fishing.The majority of prawns used in such activities belong to Macrobrachium genus.Still, according to these authors, there are several research institutions that investigate indigenous species to elaborate farming techniques that in addition to commercial ends also help to replace natural stocks.
According to Vazzoler (1982); Lobão et al. (1985) and Valenti et al. (1989) the knowledge of species fecundity is important to evaluate its potential for commercial farming, as well as an estimation of reproductive potential and the stock size of natural population.In addition, it can also be utilized to determine the minimum number of adults necessary to maintain the recruitment and egg survival rates until adulthood.Santos (1978) defined fecundity as the number of eggs laid by one female per hatching.However, Bond & Buckup (1982) defined fecundity as the number of eggs laid per hatching that was found to adhere to the female pleopods, definition to be used in the present work.Lobão et al. (1986) observed that not all eggs incubated by one female are viable, and sometimes the number of hatched larvae may be inferior to the number of eggs produced.For this reason, it is important to evaluate female fertility, that is, the number of larvae produced in the same hatching.
Due to lack of work about reproductive biology of M. amazonicum in Ceará state, this work aimed at determining fecundity and fertility of this species and their relationship with animal length and weight.

Sampling period and local
M. amazonicum were captured monthly from June 1999 to June 2001, from Jaguaribe River, Itaiçaba, Ceará, located above Work Channel dam, at 200 m altitude and 04º40'28"S and 37º49'21"W.
Jaguaribe River is 633 km long and is divided into three sub-basins: High, Medium and Low Jaguaribe, this is 137 km long and flows into the Atlantic at Aracati town.Contrary to the other two, this sub-basin is characterized by predominance of sedimentary soil compared to crystalline (Atlas do Ceará, 1995).

Sampling material
Prawns were collected by a fisherman using fishing net and transferred to Biological Science Laboratory, at Universidade Estadual do Ceará (LABIO/UECE).
In laboratory, live prawns were placed in 500 L-tanks, equipped with biological filter and plenty aeration.Daily, at the end of the afternoon, individuals were fed artificial ration for aquatic organisms at a ratio of 10% of the biomass of each tank.

Fecundity determination
Among the ovigerous females collected monthly, 60 were randomly selected to determine fecundity.
Using a caliper rule with 0.05 mm precision, it was determined: abdomen length (Lc) defined as the distance between distal extremity of rostrum and the medium point of posterior part of carapace; the length of abdomen + telson (La + t) defined as the distance between the medium point of supero-anterior edge of the first abdominal segment and the distal extremity of telson.Total length (Lt) was defined as Lc + La + t.Also, for each individual, total weight (Wt) was determined using a 0.1 g precision scale.
From each female, the eggs adhered to the pleopods were taken out using tweezers and scissors.Eggs were then placed in a plastic container filled with Gilson solution to ease the dissociation and stored in alcohol 70%.
Individual fecundity was determined from the total egg counting, using a stereoscopic microscope (10 X) with the help of a plastic camera to facilitate visualization and counting.The data referring to length of cephalothoraxes, abdomen, total length and weight of the females, coloration and number of eggs, weight and coloration of gonad were noted in an appropriate form.
To determine average fecundity, females with eggs were grouped in length (cm) and weight (g) classes.

Fertility determination
To determine fertility, M. amazonicum ovigerous females with eggs were transferred alive from the sampling place to Biological Science Laboratory and stored in 500 L-fiberglass boxes equipped with biological filter and plenty aeration.Daily, prawns were fed commercial ration at ratio of 10% of the biomass contained in each box.
Later on, females with eggs were transferred from the boxes to individual 10 L-glass-fish tanks maintained under strong aeration.Females were fed daily with fish and artificial ration for aquatic organisms.Waste ration and feces were siphoned daily and the water replaced.In addition, the general condition of the females was observed to notice the occurrence of hatching.
When hatching occurred, the larvae were attracted to the sidewall of the aquarium using directed light, since they present positive phototactism.After that, they were siphoned to a container filled with water to count the number of hatched larvae by transferring them with the help of a pipette to a second recipient.For each female that hatched, length and weight data were determined for fecundity analysis.
In a identical procedure used for fecundity analysis, data related to length of cephalothoraxes, abdomen + telson total length and weight of the female, storage date, egg color, hatching date, gonad color and number of hatched larvae were also noted in appropriate form.
From the individual data for fecundity and fertility, it was determined average fecundity and fertility for M. amazonicum females by weight and length classes.The analyzed individuals were grouped in 0.5 cm length and 0.5 g weight classes.After that, the relationship between average fecundity -length and weight, as well as average fertility -length and weight were also determined.

Influence of rain on the sampling collection
In spite of M. amazonicum females have been caught every month, the amount of prawns captured from June 1999 to June 2001 was not constant during this period.During the months of April and December 2000 and in March 2001, when the river was strongly affected by the heavy rains in the region, a total absence of individuals was observed.Apparently, this fact may be related with increasing water level due to rainfall.When the level of the river was lower, fishing was more abundant and the opposite was observed when the level was higher and consequently, the current stronger.

Average fecundity determination
Average fecundity (F) of M. amazonicum females, originated from Low Jaguaribe collected between July 1999 and June 2001, by length and weight classes can be seen in Tables 1 and 2, respectively.
For all observed length and weight classes, average fecundity was always higher than average fertility (Figs. 1 and 2).
With respect to average fecundity by length classes, the highest and lowest number of eggs observed was 1,554 and 480, respectively.As for fecundity by weight classes, the lowest number of eggs observed was 619 and the highest, 2,128 (Tables 1 and 2).
Average fecundity/total length and average fecundity/total weight may be expressed by a linear relationship represented in Figs. 3 and 4, respectively.The adjusted equations are: F = -411.6+ 203.1 L (p < 0.0001) F = 566.4+ 157.3 W (p < 0.0001) where F = average fecundity; L = total length (cm); and W = total weight (g).

Average fertility determination
Average fertility (N) of M. amazonicum females, originated from Low Jaguaribe collected between June 1999 and June 2001, by length and weight classes can be seen in Tables 1 and 2, respectively.
In the analysis of average fertility per length classes, the lowest and highest number of larvae observed was 397 and 1,301, respectively.With respect to fertility per weight classes, the lowest number of larvae was 401 and the highest, 1,915 (Tables 1 and 2).
Average fertility/total length and average fertility/total weight may be expressed by a linear relationship represented in Figs. 5 and 6, respectively.The adjusted equations are: N = -1042.7 + 264.9 L (p < 0.0002) where N = average fertility; L = total length (cm); and W = total weight (g).

DISCUSSION AND CONCLUSION
The fecundity of Macrobrachium prawns is very variable.The hightest fecundity in species of this genus is observed in M. rosenbergii and M. carcinus, which females can lay between 80,000 and 100,000 eggs in each spawning when they are fully mature.In the first spawning they can be lay not more than 5,000 and 20,000 eggs (Ismael & New, 2000).Valenti et al. (1986Valenti et al. ( , 1989) ) observed M. acanthurus females hatched about 18,000 egg, while Shokita, cited by Scaico (1992) observed females with 13,600.Although M. amazonicum captured in Lower Jaguaribe presents a smaller fecundity than those species, it presents higher fecundity than M. shokitai, whose fecundity is lower than 60 eggs, and M. jelski, M. iheringi, M. borelli, M. potiuna, and M. australiense, whose absolute fecundity is lower than 200 eggs (Shokita, cited by Scaico, 1992).
In our study, the highest number of eggs observed individually per hatching of M. amazonicum was 2,193.This result was below the 6,000 eggs per hatching reported by Coelho et al. (1982b) for M. amazonicum.However, the results reported in this work are higher than the values reported by Romero (1980) and Gamba (1984), who reported 953 and 1,000, respectively.Lobão et al. (1986) reported 1,344 eggs per hatching for females hatched in laboratory originating from Belém, Pará, and Porto (1998) reported a average fecundity of only 114 eggs.
According to Magalhães (1985), contrary to larger species, M. amazonicum may have their entire life cycle restricted to freshwater and present monthly hatchings.According to Romero, cited by Magalhães (1985) and Lobão et al. (1986) monthly hatchings may compensate for the lower fecundity, thus making commercial culture feasible.Maximum fecundity found in this work is close to results reported in literature.According to Lobão et al. (1986), the variations found for fecundity may be attributed to different conditions of female maintenance in the laboratory, female physiological conditions and season, among others.Graziani et al. (1993) explained that in Macrobrachium species the fecundity is extreme associated with the female age, and that it can increase while the female becomes mature.
The fertility of Macrobrachium prawns is very variable too.According to New (1990) the hightest fertility in this genus was observed in M. rosenbergii whose mature females can produce 80,000 larvae, while M. carcinus, with 70,000 is the second more fertile female.One other native specie, M. acanthurus has the fertility lower than the preceding species, Dugan et al. (1975) andHagood &Willis (1975), cited by Graziani et al. (1993) observed that a female can hatch 10,000 and 14,500 larvae, respectively.
According to Scaico (1992), M. amazonicum has lower fertility compared to other species of commercial value, such as M. rosenbergii.This observation is expected, as shown by the M. amazonicum fecundity is lower than those others species too.However, as this specie hatchings monthly this fact may compensate for the lower fecundity, thus making commercial culture feasible too.
Based on our results we can deduced that M. amazonicum females fecundity and fertility are lower than ones commercial species, nevertheless they can be captured during all year long.The number of captured prawns varied with the level of water in the river, it observe a large number of animals was observed in the months whose level of water was low; the inverse was observed in the months that the river was with a high volume of water.