Gonadal maturation and histological observations of the grey triggerfish Balistes capriscus Gmelin,1789(Teleostei:Balistidae)in the Gulf of Gabès,Tunisia

Objective:To determine the spawning activity using gonadosomatic index(GSI)and gonad histology the Balistes capriscus(Teleostei:Balistidae)of the Gulf of Gabès(Southern Tunisia,Central Mediterranean Sea).Methods:The reproductive biology of the species,based on 756(480 females and 276 males),collected from commercial catches at several fishing ports including Chebba,Kerkennah and Zarzis at respective GPS coordinates(34°14'N,11°06'E),(34°45'N,11°17'E),(33°41'N,11°48'E)was studied over 28 months(January 2008-April 2010)using GSI and gonad histology.Sizes used in this study ranged from 11.30 to 45.60 cm in fork length.Results:Both GSI and gonad histology suggest that spawning activity occurred mainly between July and mid-September with a peak in July,coinciding with summer time.The first maturation occurred at 20.26 cm fork length for females and 21.30 cm fork length for males.The monthly values of hepatosomatic index and condition factor(K)indicated that the liver is the main organ responsible for the mobilization process of the energizing reserves during the sexual cycle.Conclusions:It is the first inventory of gonadal maturation and histological observations of the grey triggerfish Balistes capriscus Gmelin,1789(Teleostei:Balistidae)in the Gulf of Gabès,(Southern Tunisia,Central Mediterranean Sea).

Preliminary observations on the feeding habits of the Mediterranean needlefish Tylosurus acus imperialis(Teleostei:Belonidae)

Objective:To present the first information on the feeding habits of the Mediterranean needlefish Tylosurus acus imperialis(T.a.imperialis)of Tunisia and to examine the diet variation in relation to the fish size,maturity and sex.Methods:Gut contents of 92 specimens of T.a.imperialis,collected mainly from May 2004 to July 2006 off the Gulf of Gabès,Southeastern Tunisian coast,were analyzed.Results:The results showed that 55.4%of them had empty guts and 44.6%contained food in their guts.The emptiness index did not vary significantly according to size classes or sexes of T.a.imperialis.Basic food consisted of teleosts(Mugilidae,Gobidae and Belonidae)(59.63%)followed by crustaceans(40.24%),mostly decapods Sycionia carinata(5.42%).A decrease in the feeding rate at the peak of the spawning season was observed for both sexes.A diet variation among juvenile and adult specimens of T.a.imperialis was found.Conclusions:This study enhances our knowledge on the biology of the Mediterranean needlefish T.a.imperialis.This fish is an active predator and an opportunistic feeder but the feeding rate declines at the peak of the spawning season.

Influence of season,size and sex on the dynamic of gill metazoan parasite infesting the Balistes capriscus(Teleostei:Balistidae)of the Gulf of Gabès(Tunisia)

Objective:To investigate the effects of season,size and sex on the dynamic of gill metazoan parasite infesting the Balistes capriscus(Gmelin,1788)(Teleostei:Balistidae)(B.capriscus)of the Gulf of Gabès(Southern Tunisia,Central Mediterranean Sea).Methods:A parasitological survey of the grey triggerfish B.capriscus from the Gulf of Gabès(Southern Tunisia,Central Mediterranean Sea)was conducted monthly from June 2011 to June 2012.A total of 1080 fish were collected from commercial catches by pelagic trawl net at different fishing ports at Chebba(34°14'N,11°06'E),Kerkennah(34°45'N,11°17'E)and Zarzis(33°41'N,11°48'E).The weight,size,sex,date and area of capture of each specimen were recorded.Then,B.capriscus was examined to search for ectoparasites.For each parasite species,parasitological indices were calculated.Results:The parasite species are indentified as two copepods:Naobranchia variabilis,Taneacanthus ballistae and a monogenean:Ancyrocephalus balisticus.The parasitological indices depend significantly on seasonality;the highest prevalence of Naobranchia variabilis,Taneacanthus ballistae and Ancyrocephalus balisticus(28.89%,35.93%and 55.56%respectively)was recorded during summer season(June–August),while the lowest prevalence of each(6.3%,4.44%,8.15%)recorded during winter season(December–February).Furthermore the parasitological indices depend significantly on the host size but not on host sex.Conclusions:Our data suggest that the dynamic of gill metazoan parasite infesting B.capriscus is a result of a complex of biotic and abiotic factors.It is the first study on the effects of season,size and sex on the dynamic of gill metazoan parasite infesting B.capriscus(Teleostei:Balistidae)of the Gulf of Gabès(Southern Tunisia,Central Mediterranean Sea).