Sex-ratio, reproduction and feeding habits of Pomadasys incisus (Haemulidae) in the Gulf of Tunis (Tunisia)

Istraživane su reprodukcija i prehrambene navike morskog hroktača, Pomadasys incisus (Bowdich, 1825), u tuniskom zaljevu od siječnja do prosinca 2003. Istraživanje gonada na 463 uzorka je pokazalo da je morski hroktač gonohorična vrsta i da odnos među spolovima nije značajno odstupao od razmjera 1:1. Mjesečna kolebanja gonadosomatskog indeksa i postotka različitih stadija razvoja gonada otkrivaju da se P. incisus mrijesti od kolovoza do listopada. Ova vrsta koristi energetske pričuve iz jetre i mišića kako bi osigurala sazrijevanje gonada. Izračunata dužina pri stadiju 50% zrelosti populacije (L50) iznosila je 15.33 cm za oba spola ukupno. Analizirani sadržaj želuca je pokazao vrlo visoki indeks ispražnjavanja tijekom godine (56.8%) sa značajnom razlikom između sezona (godišnjih doba). Ustanovljeno je također da se prehrana P. incisus sastoji od rakova, bentičkih i planktonskih organizama iz 19 taksonomskih skupina. Postotak učestalosti pojavljivanja pronađen za Crangon crangon, Hyperoche sp. i Geryon longipes (najzastupljenije u prehrani) ukazuje na značajne razlike među sezonama (χ2obs= 31.228, 29.471 odnosno 11.302, a bile su veće od χ20.05).The reproduction and feeding habits of the Bastard grunt, Pomadasys incisus (Bowdich, 1825), in the Gulf of Tunis were investigated monthly from January to December 2003. An examination of the gonads of 463 specimens showed that the Bastard grunt is a gonochoric species and the sexratio wasn’t significantly different from 1:1. The monthly variations of the gonadosomatic index and the percentage of the different gonadal development stages revealed that P. incisus spawning period occurred from August to October. This species uses its energetic reserves contained in the liver and the muscles to assure gonadal maturation. The size at first maturity (L50) was estimated at 15.33 cm for both sexes pooled. The stomachs examined showed a high vacuity index throughout the year (56.8%) and presented a significant difference between seasons. The stomach contents analysis revealed that P. incisus’ diet was especially constituted of crustacean species as well as benthic and planktonic organisms that belong to 19 taxa. The percentage frequency of occurrence (F) computed for Crangon crangon, Hyperoche sp. and Geryon longipes (the most abundant prey in the diet) showed significant differences among seasons (χ2obs=31.228, 29.471 and 11.302 respectively, were superior to χ20.05)

Sex-ratio, reproduction and feeding habits of Pomadasys incisus (Haemulidae) in the Gulf of Tunis (Tunisia)

Istraživane su reprodukcija i prehrambene navike morskog hroktača, Pomadasys incisus (Bowdich, 1825), u tuniskom zaljevu od siječnja do prosinca 2003. Istraživanje gonada na 463 uzorka je pokazalo da je morski hroktač gonohorična vrsta i da odnos među spolovima nije značajno odstupao od razmjera 1:1. Mjesečna kolebanja gonadosomatskog indeksa i postotka različitih stadija razvoja gonada otkrivaju da se P. incisus mrijesti od kolovoza do listopada. Ova vrsta koristi energetske pričuve iz jetre i mišića kako bi osigurala sazrijevanje gonada. Izračunata dužina pri stadiju 50% zrelosti populacije (L50) iznosila je 15.33 cm za oba spola ukupno. Analizirani sadržaj želuca je pokazao vrlo visoki indeks ispražnjavanja tijekom godine (56.8%) sa značajnom razlikom između sezona (godišnjih doba). Ustanovljeno je također da se prehrana P. incisus sastoji od rakova, bentičkih i planktonskih organizama iz 19 taksonomskih skupina. Postotak učestalosti pojavljivanja pronađen za Crangon crangon, Hyperoche sp. i Geryon longipes (najzastupljenije u prehrani) ukazuje na značajne razlike među sezonama (χ2obs= 31.228, 29.471 odnosno 11.302, a bile su veće od χ20.05).The reproduction and feeding habits of the Bastard grunt, Pomadasys incisus (Bowdich, 1825), in the Gulf of Tunis were investigated monthly from January to December 2003. An examination of the gonads of 463 specimens showed that the Bastard grunt is a gonochoric species and the sexratio wasn’t significantly different from 1:1. The monthly variations of the gonadosomatic index and the percentage of the different gonadal development stages revealed that P. incisus spawning period occurred from August to October. This species uses its energetic reserves contained in the liver and the muscles to assure gonadal maturation. The size at first maturity (L50) was estimated at 15.33 cm for both sexes pooled. The stomachs examined showed a high vacuity index throughout the year (56.8%) and presented a significant difference between seasons. The stomach contents analysis revealed that P. incisus’ diet was especially constituted of crustacean species as well as benthic and planktonic organisms that belong to 19 taxa. The percentage frequency of occurrence (F) computed for Crangon crangon, Hyperoche sp. and Geryon longipes (the most abundant prey in the diet) showed significant differences among seasons (χ2obs=31.228, 29.471 and 11.302 respectively, were superior to χ20.05)

La dieta de Pagellus acarne (Sparidae) en el golfo de Túnez, Mediterráneo central

The feeding habits of the axillary seabream, Pagellus acarne (Risso, 1810), from the Gulf of Tunis were investigated in relation to season, sex and fish size (juveniles TL < 14.5 cm and adults TL &#8805; 14.5 cm). A total of 536 specimens (males, females, unsexed and hermaphroditic), ranging between 11.0 and 25.2 cm TL, were collected with trammel nets from June 2005 to July 2006. Their stomach contents were analysed. Of the total number of examined stomachs, 279 stomachs were empty (Vacuity index, VI = 52%). The VI did not reveal significant seasonal differences when all of the specimens were analysed together; however, significant seasonal variations were observed for females. The diet of the axillary seabream was composed of 36 different prey species. The most important prey were Arthropoda, Mollusca and Echinodermata. Both the dietary indices and the Spearman’s coefficient of correlation indicated seasonal variations in the diet. The diet was more diversified in adults than in juveniles. The axillary seabream fed on a wide range of prey items, endofauna and nekton, and can be considered a carnivorous and euryphagous predator.Se estudió la dieta del aligote, Pagellus acarne (Risso, 1810), del golfo de Túnez en función de las estación del año, del sexo y de dos grupos de talla: juveniles (LT < 14.5 cm) y adultos (LT ≥ 14.5 cm). Entre junio 2005 y julio 2006 se recolectaron con trasmallos, un total de 536 ejemplares (machos, hembras, sexos no determinados) cuya longitud total oscilaba entre 11 y 25.5 cm. Se analizó el contenido estomacal; 279 estaban vacíos (índice de vacuidad, VI = 52.0%). Este índice no reveló diferencias significativas en relación a la estación del año. Sin embargo, se observaron importantes variaciones estacionales para las hembras. Se identificaron un total de 36 especies de presas en la dieta. Las más frecuentes eran artrópodos, moluscos y equinodermos. Los índices de alimentación calculados, así como la aplicación del coeficiente de correlación de Spearman, mostraron variaciones estacionales. El análisis específico de las presas evidenció que la dieta de los machos era diferente a la de las hembras y era más variada en los adultos que en los juveniles. P. acarne se alimenta de un amplio espectro de presas, endofauna y necton, y podría considerarse como depredador carnívoro y eurífago

Impact of a blood-sucking parasite on the chemical composition of fatty acids in the white muscle of garfish (Belone belone, Belonidae) from Tunisian coasts (Central Mediterranean)

The objective of this study was to compare the composition of fatty acids in the garfish (Belone belone) white muscle removed from parasitized and non parasitized specimens. The chemical analysis results revealed low contents of total fatty acids for both parasitized and non-parasitized specimens. Their values, less than 2 g/100 g of fresh muscle, allowed the classification of the garfish as a lean fish. High ratios of saturated fatty acids were found in the garfish muscle reaching 58.4% of total fatty acids. These fatty acids were represented mainly by lauric, miristic and palmitic at a level of 50.3%. As a lean fish, garfish contains 16% polyunsaturated fatty acids (n-3). Two major fatty acids are docosahexaenoic and eicosapentaenoic with respective percentages of 9 and 1.17% of total fatty acids. The parasitized garfish showed increase in their fatty acids, mainly in pentadecanoic, pentadecenoic, docosahexaenoic and arachidonic acids and decreases in saturated acids especially lauric, miristic and palmitic. This drop is correlated with a very significant increase in PUFA from 16 to 26% of total fatty acids. In order to obtain 0.5 g/day of EPA + DHA, the amount of garfish required is 641 g of non-parasitized and 436 g parasitized fish.Key words: Garfish, blood-sucking, parasite, parasitized fish, fatty acid analysis, Tunisia

Crecimiento y contenido de larvas de atún rojo (Thunnus thynnus) y atún blanco (Thunnus alalunga)

The waters surrounding the Balearic archipelago are considered to be prime spawning habitats of the bluefin tuna (Thunnus thynnus) and other tuna species such as albacore (T. alalunga) in the Mediterranean. During the 2003 bluefin and albacore spawning season, a tuna larval survey (TUNIBAL 0703) was carried out to assess the distribution of bluefin larvae in relation to hydrographic mesoscale features. Tuna larvae were collected by means of surface plankton tows with a bongo gear with a quadrangular mouth measuring 1 m diagonally. The otolith microstructure of 157 and 71 field-captured larvae of Mediterranean bluefin and albacore, respectively, were analyzed to estimate the daily growth pattern. Furthermore, biochemical analysis to estimate DNA, RNA and protein content was done on another batch of 114 bluefin and 132 albacore larvae. The size range included pre-flexion to post-flexion larvae, from 2.8 to 8.6 mm in body length. bluefin and albacore larvae grew linearly in standard length (0.35 and 0.33 mm/day, respectively) and potentially with respect to dry weight. No significant differences between species were observed in the size-weight relationship, or in the allometric relationship of body size and weight to otolith radius. However, the relationship of DNA and RNA to body size and weight showed a significant difference between species. Bluefin tuna larvae showed a greater nucleic acid content than albacore larvae. Protein content showed no significant differences with respect to body length.Las aguas de las Islas Baleares representan una de las zonas m&aacute;s importantes de puesta del at&uacute;n rojo (Thunnus thynnus) y de otras especies asociadas, como el at&uacute;n blanco albacore (T. alalunga). En julio del 2003, &eacute;poca de puesta del at&uacute;n, se realiz&oacute; la campa&ntilde;a TUNIBAL, con el fin de delimitar las zonas de puesta del at&uacute;n rojo, as&iacute; como su relaci&oacute;n con el modelo de circulaci&oacute;n en el &aacute;rea. Las larvas de atunes se muestrearon mediante arrastres superficiales con una red Bongo de boca cuadrangular (1 m en diagonal). Para el estudio del crecimiento diario, 157 larvas de at&uacute;n rojo y 71 larvas de at&uacute;n blanco fueron analizadas. Para el estudio de la condici&oacute;n larvaria (DNA, RNA y prote&iacute;nas), 119 larvas de at&uacute;n rojo y 138 larvas de at&uacute;n blanco fueron analizadas. Se analizaron larvas desde estados de pre-flexi&oacute;n a post-flexi&oacute;n, desde 2.8 a 8.6 mm de longitud est&aacute;ndar. Las larvas de at&uacute;n rojo y at&uacute;n blanco crecen linealmente en longitud est&aacute;ndar (0.35 y 0.33 mm/d&iacute;a respectivamente) y potencialmente en peso seco. No se encontraron diferencias significativas en la relaci&oacute;n talla-peso, o en la relaci&oacute;n del radio del otolito con talla o peso. Sin embargo, la relaci&oacute;n entre DNA y RNA con talla o peso mostr&oacute; diferencias significativas entre especies, siendo el at&uacute;n rojo el que mostr&oacute; mayores contenidos en &aacute;cidos nucleicos. No obstante, el contenido en prote&iacute;nas no mostr&oacute; diferencias significativas con la talla entre especies

First data on growth and nucleic acid and protein content of field-captured Mediterranean bluefin (Thunnus thynnus) and albacore (Thunnus alalunga) tuna larvae: a comparative study

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