REARING OF JUVENILE DARK CRABS, CALLINECTES RATHBUNAECONTRERAS, 1930, UNDER LABORATORY CONDITIONS

BY

SERGIO CHÁZARO-OLVERA1,2), HORACIO VÁZQUEZ-LÓPEZ1,3) andANGEL MORÁN-SILVA1,4)

1) Laboratorio de Ecología de Crustáceos, Facultad de Estudios Superiores Iztacala, UniversidadNacional Autónoma de México, Apartado Postal 314, Tlalnepantla, Estado de México, C.P. 54090,

Mexico

ABSTRACT

In the present study, we reared juvenile dark crabs, Callinectes rathbunae under laboratoryconditions. We determined growth rate, increase in carapace width, moult consumption, regenerationof appendages, and survival. The crabs were collected in March 2004 from the Alvarado LagoonSystem in the state of Veracruz, Mexico. Crabs were transported to the laboratory and acclimated to5 and 15 psu and a temperature of 25 ± 1◦C. Growth rate was determined by the difference in sizeat the time interval between the pre-moult and moult stages. Survival was assessed by counting thejuvenile crabs during rearing, moult consumption was determined after 24 hours, and regenerationof appendages at the next moult. The size of juveniles ranged from 1.7 to 6.4 cm. Results revealedthat carapace increase was greater at 15 psu, being 35.29% for the 1.7-2.8 cm size range. The meangrowth rate at 5 psu was 0.33±0.07 mm/day and 0.76±0.12 mm/day at 15 psu. Moult consumptionwas 50%. A 100% regeneration of appendages was observed after moulting. Survival was best at 15psu, with 78.31%.

RESUMEN

En el presente estudio se realizó el cultivo de cangrejos juveniles de Callinectes rathbunae encondiciones de laboratorio. Se determinó la tasa de crecimiento, el incremento en el ancho delcaparazón, el consumo de la muda, la regeneración de apéndices y la sobrevivencia. La colectase realizó en Marzo de 2004 en el Sistema lagunar de Alvarado, Veracruz, México. Los cangrejosfueron transportados al laboratorio y aclimatados a 5 y 15 ups y temperatura de 25 ± 1◦C. La tasade crecimiento se determinó por la diferencia de talla y el intervalo de tiempo transcurrido entre lapremuda y la postmuda, la sobrevivencia por el conteo de cangrejos juveniles durante el tiempo decultivo, el consumo de la muda después de 24 h y la regeneración de los apéndices a la siguientemuda. El intervalo de talla de los juveniles fue de 1,7 a 6,4 cm. Los resultados mostraron que el

2) e-mail: chazaro@campus.iztacala.unam.mx3) e-mail: hvazquez@campus.iztacala.unam.mx4) e-mail: amorans@servidor.unam.mx

© Koninklijke Brill NV, Leiden, 2007 Crustaceana 80 (2): 161-170Also available online: www.brill.nl/cr

162 SERGIO CHÁZARO-OLVERA ET AL.

incremento en el ancho del caparazón fue mayor en una salinidad de 15 ups con el 35. 29% enel intervalo de talla de 1,7 a 2,8 cm. Las tasa de crecimiento promedio a 5 ups fue de 0,33 ±0,07 mm/día y a 15 ups fue de 0,76 ± 0,12 mm/ día. El consumo de muda fue del 50%. Se observó un100% de regeneración de apéndices después de la muda. El porcentaje de sobrevivencia fue mayora 15 ups con el 78,31%.

INTRODUCTION

Crabs of the genus Callinectes are considered benthic macroinvertebrates,predominately present on the coasts of North and South America (Chávez &Fernández, 1976; Ettinger & Byle, 1981; Rosas, 1989; Rosas et al., 1994; Cházaro-Olvera et al., 2000). Eleven species of Callinectes have been recorded in Mexico;among these, C. rathbunae Contreras, 1930, C. sapidus Rathbun, 1896, and C.similis Williams, 1966 predominate in the Gulf of Mexico (Williams, 1974, 1984).

Callinectes rathbunae is a species (Raz-Guzman et al., 1992) distributed fromthe south of Texas to the Laguna de Términos in the state of Campeche, Mexico(Williams, 1974; Powers, 1977; Raz-Guzmán et al., 1992; Rocha et al., 1992;Cházaro-Olvera et al., 2000). The largest abundance of C. rathbunae has beenrecorded in the Alvarado Lagoon, state of Veracruz, Mexico (Chávez & Fernández,1976; Rosas, 1989). From an ecological point of view, these organisms areclassified as euryhaline, and are found in shallow waters of the coast, estuaries,and lagoons, at depths between 0.40 and 90 m and at temperatures above 20◦C(Cházaro-Olvera & Peterson, 2004).

Callinectes fisheries in Mexican waters are restricted almost exclusively to theGulf of Mexico; it is estimated that more than 90% of the total catch consumed inthe country comes from the states of Veracruz and Tamaulipas (Cházaro-Olvera etal., 2000). The dark crab, C. rathbunae and the blue crab, C. sapidus are the mainspecies supporting commercial crab fisheries in Mexico (Álvarez & Calderón,1996).

In recent years the crab fishery has been increasing in Mexico, because ofthe closed-season imposed on the shrimp fishery (Cházaro-Olvera, 2002) and theincrease in yields through soft-crab catches. It therefore becomes relevant to knowand improve the rearing techniques currently used to increase productivity, anddecrease maintenance costs. The present study was aimed at assessing the increasein carapace width of C. rathbunae juveniles, their growth rate, survival, percentageof moult consumption, and regeneration during the rearing time in a continuous,re-circulating system at 5 and 15 psu.

REARING OF CALLINECTES RATHBUNAE 163

MATERIAL AND METHODS

Juvenile Callinectes rathbunae were collected in the Alvarado Lagoon System,state of Veracruz, located at 18◦50′-18◦52′N 95◦42′-95◦58′W; the systems majoraxis is parallel to the coast (fig. 1). The maximum recorded water temperature was30◦C and the minimum 19◦C; maximum salinity was 34.2 psu (practical salinityunits) and minimum 0.0 psu; average current flow was 0.65 m/s; and dissolvedoxygen averaged 7.11 mg/l.

Crabs were collected in the juvenile stage in the northeastern part of the lagoonsystem between 6:00 and 11:00 h, which are the main catching hours used bythe fishermen. Collection was accomplished with “crab rings”, which have anapproximate diameter of 40 cm and a net mesh size of 1.35 cm.

Crabs were transported in 5-l plastic containers, with 20 specimens per con-tainer, each provided with a portable aeration pump (Elite 801). In addition, waterfrom the sampling site, previously filtered through a 250-µm mesh, was trans-ported in 50-l containers, which allowed for total water exchange every two hoursduring transport to the laboratory. Once in the laboratory, the organisms were ac-climated slowly until reaching a temperature of 25 ± 1◦C and salinities of 5 and15 psu. Salinity was maintained by preparing water with Instant Ocean® salt.

Five class intervals were set up with the sizes recorded (Canavos, 1988),obtaining the frequency per interval and the sex ratio (Dreux, 1984).

To rear the crabs, we constructed a continuous circulating system (fig. 2). Waterwas supplied through a submersible pump, “Little Giant” model 2E-28N, placed on

Fig. 1. The Alvarado Lagoon System, state of Veracruz, Mexico.

164 SERGIO CHÁZARO-OLVERA ET AL.

Fig. 2. Continuous recirculation system as used in the rearing experiments.

the lower part of the system in a 40-l container. Eight juvenile crabs were placed inthe container when carapace width was smaller than 2 cm and four juveniles whensizes were 3-6 cm. Water was completely exchanged every 10 days to maintainadequate water quality.

The crabs were fed with small fishes of the family Poecilidae: Poeciliopsisgracilis Heckel, 1848; Poeciliopsis balsas Hubbs, 1926; Poeciliopsis lucida Miller,1960; and Poecila formosa Girard, 1859. Once a day, crabs were fed an amountequivalent to 10-15% of their own weight (Cházaro-Olvera, 1996). After 24 h, thecarapaces of moulted individuals were measured with 0.1-mm precision Verniercallipers.

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Growth rate in millimeters per day and percentage increase per moult wereassessed according to the criteria proposed by Paul (1981). We determined thepercentual moult consumption after leaving the moult for 24 h in the container. Thepercentage of regenerations was determined at the time of the next moult in thoseindividuals that lacked an appendage. The percentage survival was obtained bycounting juveniles throughout the rearing period (Alvarez et al., 1995), subjectedto analysis of variance (ANOVA); data were arcsine transformed prior to analysis(Sokal & Rohlf, 1995).

RESULTS

We caught 140 juvenile Callinectes rathbunae. The class intervals and theirrespective abundances were integrated as follows: In the 1.7-2.8 cm interval, a3.26% abundance was recorded; 2.9-4.0 cm, 13.04%; 4.1-5.2 cm, 63.05%; 5.3-6.4 cm, 18.47%; and 6.5-7.6, 2.17% (fig. 3). Seventy specimens were used foreach salinity treatment; the sex ratio was 1 female : 0.94 male. For the 5 psu trial,the highest increase in carapace width was for the 1.7-2.8 cm interval with 28.96-34.26% and the lowest increase for the 5.3-6.4 interval with 14.54-20.83%. Forthe 15 psu trial, the highest increase in carapace width was also for the 1.7-2.8 cminterval with 29.32-35.29% and the lowest increase for the 6.4-7.6 cm interval with7.45-12.30% (table I).

The growth rate obtained for both sexes at 5 psu averaged 0.33 ± 0.07 mm/day;the mean was 0.39 ± 0.09 mm/day for females and 0.29 ± 0.05 mm/day for males.

Fig. 3. Callinectes rathbunae Contreras, 1930. Size frequencies of juvenile crabs caught in theAlvarado Lagoon System, Veracruz, Mexico, during 2004.

166 SERGIO CHÁZARO-OLVERA ET AL.

TABLE ICallinectes rathbunae Contreras, 1930. Increase in carapace width at 5 and 15 psu

Size interval (cm CW) Percentage increase: 5 psu Percentage increase: 15 psu

1.7-2.8 28.96-34.26 29.32-35.292.9-4.0 18.10-37.50 8.33-16.664.1-5.2 8.51-22.40 7.69-13.635.3-6.4 14.54-20.83 13.79-34.486.5-7.6 15.46-23.15 7.45-12.30

Fig. 4. Callinectes rathbunae Contreras, 1930. Survival of juvenile crabs: 2, at 15 psu salinity; ", at5 psu salinity.

The growth rate at 15 psu for both sexes was 0.76 ± 0.12 mm/day, with a mean of0.66 ± 0.10 mm/day for females and 0.86 ± 0.11 mm/day for males.

Survival was 54.45% at 5 psu and 78.31% at 15 psu (fig. 4): this means asignificantly lower percentage survival for C. rathbunae (P < 0.001) at 5 psu.

All appendages regenerated fully through the next moulting cycle at bothsalinities. The average percentage of exuvia consumption was 50% for bothsalinities; a higher exuvia consumption frequency was observed for the 4.7-5.2 cmsize interval.

DISCUSSION

Only 20% of the Callinectes rathbunae catch was above 6.0 cm. The highestsize frequency was recorded between 4.1 and 6.4 cm. Román-Contreras (1986)used similar catching gear in the Laguna de Términos, Campeche, and recorded

REARING OF CALLINECTES RATHBUNAE 167

the highest abundance of juvenile crabs in sizes between 2.0 and 6.0 cm; García-Kauffman & Franco-López (1989) found, in the Camaronera Lagoon, crabsbetween 1.5 and 7.5 cm using crab rings of the same characteristics as we did.

The sex ratio (1 : 0.94) was quite close to 1 : 1. Ramírez & Hernández (1988)reported a 1 : 1 sex ratio in a sample of 741 C. rathbunae in the Alvarado Lagoon,in the state of Veracruz.

The percentages in carapace increase found in the present study are similarat both salinities, with highest values for the 1.7-2.8 interval (28.96-35.29%).Guerin & Stickle (1997a, b) found that, at 5 psu, Callinectes similis increased16.00 ± 1.40% and at 30 psu the increase was 19.69 ± 1.64%. Tagatz (1968)reported a 24.3% increase for C. sapidus in 5.0-5.9 cm organisms maintainedat 18.8 psu and a temperature of 26.8◦C. Dittel & Epifanio (1984) observed anincrease in carapace width in C. arcuatus Ordway, 1863, of 21-44.8% at 25 psu.Ramírez & Hernández (1988) calculated a 22.5 ± 3.5% increase, at 25 psu for C.rathbunae.

The growth rates obtained in this study were higher at 15 psu. Van Engel(1958) and Tagatz (1968) reported a growth rate of 0.33 mm/day in C. sapidus inFlorida waters. Quijano-Fernández (1985) reported for C. arcuatus a growth rate of0.33 mm/day in males and of 0.26 mm/day in females in the Huizache-Caimaneroregion, state of Sinaloa, Mexico; Paul et al. (1983) observed, for the same species,values of 0.53 mm/day for males and 0.59 mm/day for females. Darnell (1959)and Jaworski (1972) mentioned that C. sapidus presents a growth rate between0.53 and 0.56 mm/day in Louisiana (U.S.A.). Perry (1975) reported a highergrowth rate for C. sapidus (0.83 mm/day) in the Mississippi river. Vázquez (1996)recorded, under laboratory conditions, a growth rate of 0.39 and 0.50 mm/day forC. sapidus females and males, respectively. C. similis presented a growth rate of0.30 mm/day for females and 0.28 mm/day for males, and C. rathbunae showed arate of 0.26 mm/day in females and 0.30 mm/day in males. However, these growthrates are lower that those found for C. rathbunae in the present work at 15 psu.Raz-Guzman et al. (1992) mentioned that C. rathbunae can be found at a salinityrange of 0 to 16.7 psu, hence it can develop satisfactorily at 15 psu.

It was observed that exuvia consumption increased at the lower salinity. Vigh& Dendinger (1982) indicated that this is related to a need for higher calciumincorporation for somatic purposes, such as the production of tissues, and forphysiological functions, such as ionic regulation. The percentage of appendageregeneration was 100% at both salinities. It is worthwhile mentioning that theseorganisms have the capacity to get rid of their appendages (autotomy) as an escapestrategy; these are then regenerated in the course of one or more subsequentmoulting cycles. However, regeneration does not occur when specimens are in

168 SERGIO CHÁZARO-OLVERA ET AL.

adverse conditions (Skinner, 1985), as in the case of diseases or parasitism causedby rhizocephalans (Reinhard, 1950; Overstreet, 1993).

The highest survival was recorded at 15 psu with 78.31%. Ramírez & Hernández(1988) reared C. rathbunae in an open culture in Alvarado, Veracruz, and recordeda survival of 80% in organisms of the 7.2-12.05 cm class, which is similar to theobservations made in this study. On the other hand, Guerin & Stickle (1997a, b),who reared C. sapidus under laboratory conditions, confirmed the link betweensalinity and survival; they recorded a survival of 41, 66, and 75% at salinities of 2.5,10, and 30 psu, respectively.

ACKNOWLEDGEMENTS

Funding for this research was provided by the PAPIME EN203804 project ofthe UNAM. We acknowledge numerous students at the U.N.A.M.-FES-Iztacalacampus for their assistance in this project.

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First received 11 May 2006.Final version accepted 26 September 2006.