Some aspects of the biology of the female blue crab Callinectes amnicola(De Rocheburne)from the Cross River estuary,Nigeria

Objective:To investigate some important aspects of the biology of Callinectes amnicola(C.amnicola)such as fecundity,carapace length-weight relationship,condition factor and carapace length frequency distribution from the Cross River estuary,Nigeria.Methods:A total of one hundred and twenty ovigerous females of C.amnicola,freshly caught with basket traps,lift net trap,and gill net were collected from the catches of the artisanal fisheries in the study area between June 2012 and May 2013.Fecundity,carapace length-weight relationship,condition factor and carapace length frequency distribution were determined and analyzed following standard methods.Results:Fecundity(F)ranged between 73090 eggs for crab of carapace length 8.1 cm and total weight 34 g and 809450 eggs for crab of carapace length 16.1 cm and total weight 395 g with a mean of 311808.93±17693.94 eggs.There was a positive significant relationship between fecundity and carapace length,total weight and condition factor as follows:F=6839.7CL^(1.4403)(r^(2)=0.2145,P<0.05),F=15302TW^(0.5798)(r^(2)=0.4079,P<0.05),F=147255K^(0.2788)(r=0.2717,r^(2)=0.0738,P<0.05).A significant linear relationship between carapace length and weight of C.amnicola is given by the equation:Log W=2.0447LogL–0.1389(r^(2)=0.3357,P<0.05).The crab exhibited a negative allometric growth pattern(b=2.0447).Condition factor ranged between 21.48 to 104.95 with a mean value of 47.21±2.17.The carapace length frequency distribution showed a unimodal class size distribution.Conclusions:Findings of this study is crucial in assessing the population dynamics and development of management strategies of the the Blue crab,C.amnicola from the estuary such as mesh size regulation,fishing season and fishing ground regulation in the Cross River estuary.Also,findings of this study will be useful in evaluation of the aquaculture potential of the Blue crab C.amnicola,which is a valuable shell fish for the inhabitants estuary.

Monogenean parasites of the African catifsh Clarias gariepinus from two ifsh farms in Calabar,Cross River State,Nigeria

Objective:To determine the prevalence,mean intensity,and abundance of monogenean parasites in Clarias gariepinus(C.gariepinus)from two selected fish farms in Calabar,Cross River State,Nigeria.Methods:Eighty specimens of C.gariepinus from the two farms(40 each)were necropsied for parasitological analysis.Skin,gill and fin biopsies were prepared from each specimen following standard methods for microscopic analysis.Parasitological indices including dominance(D),prevalence,mean intensity and abundance were calculated according to standard formulae.Data were analyzed using the Fisher's exact test.Results:C.gariepinus from the two farms were infested with a total of ninety individuals of monogenean parasites belonging to three species including Macrogyrodactylus clarii(M.clarii),Gyrodactylus sp.and Dactylogyrus sp.D index showed that the three monogenean species were eudominant(D-value>10%).Gyrodactylus sp.was more abundant(46)followed by Dactylogyrus sp.(23)while M.clarii was the lowest(21).Prevalence,meaning intensity and abundance of monogenean parasites in the two farms,varied insignificantly higher(P>0.05).Prevalence in both farms were higher in female C.gariepinus than that in male.Monogenean parasites exhibited organ specificity as M.clarii and Dactylogyrus sp.were recovered from the gills while Gyrodactylus sp.colonized the skin and fin.Conclusions:High abundance of these parasites may lead to poor growth performance and high mortality in C.gariepinus,leading to huge monetary loss and low profit margin by increasing production cost due to the cost of treatments.