COBIA (Rachycentron canadum)

discontinuous germinal epithelium, although residual sperm are nearly always present in the lobulesand ducts. The presence or absence of sperm is not an accurate indicator of reproductive classes. Atthe periphery of the testis in the regression and regressed classes, the distal portions of lobuleselongate as cords of cells containing spermatogonia and Sertoli cells. All reproductive classes canbe identified in paraffin sections, although plastic sections provide better resolution. Usingmaturation classes defined by changes in the germinal epithelium to describe testicular developmentand spermatogenesis gives a more accurate picture than does using the traditional terminology.8. Brown-Peterson, N.J., Overstreet, R.M., Lotz, J.M., Franks, J.S. & Burns, K.M. (2001).Reproductive biology of cobia, Rachycentron canadum, from coastal waters of the southern UnitedStates. Fishery Bulletin, 99(1),15-28.Reproductive biology of the cobia, Rachycentron canadum, is described from four coastal areas inthe southern United States. Samples were obtained from recreational fishermen between December1995 and November 1997 from the southeastern United States (Morehead City, NC, to CapeCanaveral, FL), the eastern Gulf of Mexico (Ft. Myers to Crystal River, FL), the north-central Gulfof Mexico (Destin, FL, to Chandeleur Islands, LA) and the western Gulf of Mexico (Port Aransas,TX). Histological evidence of spawning occurred from April through September in all areas. Somefemale cobia (17-32%) throughout the Gulf of Mexico had spent or regressed ovaries by July.Gonadosomatic index peaked between May and July throughout the region. Ovaries of femalesfrom all areas contained both postovulatory follicles (POF) and oocytes in final oocyte maturation(FOM) during all months of the reproductive season. Batch fecundity was calculated by using threedifferent methods: oocytes >700 µm were fixed in 1) Gilson's fixative or 2) 10% neutral bufferedformalin (NBF), and 3) oocytes undergoing FOM were sectioned for histological examination.Mean batch fecundity ranged from 377,000 ± 64,500 to 1,980,500 ± 1,598,500 eggs; there was nosignificant difference among methods. Batch fecundity calculated with the NBF method showed apositive relationship with fork length (P=0.021, r 2 =0.132) and ovary-free body weight (OFBW;P=0.016, r 2 =0.143). Relative batch fecundity was not significantly different among months duringthe spawning season and averaged 53.1 ± 9.4 eggs/g OFBW for the NBF method and 29.1 ± 4.8eggs/g OFBW for the FOM method. Although spawning frequencies were not significantlydifferent among areas (P=0.07), cobia from the southeastern United States and north-central Gulf ofMexico were estimated to spawn once every 5 days, whereas cobia from the western Gulf ofMexico were estimated to spawn once every 9 to 12 days.9. Burkey, K., Young, S.P., Smith, T.I.J. & Tomasso, J.R. (2007). Low-salinity resistance ofjuvenile Cobias. North American Journal of Aquaculture, 69(3), 271-274.Juvenile cobias Rachycentron canadum were exposed to decreasing salinity (~1‰ per day) in aseries of five experiments to assess their low-salinity resistance. All fish survived for 24 h at asalinity of 2‰, but 73% died within 24 h of a reduction to 1‰ salinity. Plasma osmolalitydecreased significantly with decreasing salinity. Fish held for 7 d at 2, 5, or 8‰ after anapproximately 1‰ daily reduction differed significantly in plasma osmolality; fish held at a salinityof 2‰ exhibited significantly lower plasma osmolality than fish in the other treatments. Doublingthe environmental Ca concentration did not affect plasma osmolality. The results indicate thatcobias have limited euryhaline abilities but not enough to sustain low-salinity culture operations.10. Cai, Y., Rooker, J.R. & Gill, G. (2006). Bioaccumulation of mercury in pelagic fishes in NW Gulfof Mexico and its relationship with length, location, collection year, and trophic level. In:Proceedings of the Gulf and Caribbean Fisheries Institute, 5, 317-326.Total mercury (Hg) concentrations were determined in the tissues of 11 species of pelagic fishes,with a special emphasis on apex predators (large vertebrates). Highest mercury concentrations wereobserved in blue marlin (Makaira nigricans), Carcharhinid sharks (genus Carcharhinus) and littletunny (Euthynnus alletteratus), ranging from 1.0 to 10.6 ppm. Moderate to low concentration (< 1.0ppm) were observed in greater amberjack (Seriola dumerili), blackfin tuna (Thunnus atlanticus),cobia (Rachycentron canadum), king mackerel (Scomberomorus cavalla), little tunny (Euthynnusalletteratus), wahoo (Acanthocybium solandri), yellowfin tuna (Thunnus albacares) and dolphinfish(Coryphaena hippurus). For the majority of species examined, contaminant loads of mercury didnot vary significantly between two consecutive years (2002 and 2003) and between two adjacentlocations (Texas and Louisiana). The relationship between Hg concentration and fish size was alsoexplored in certain species. Several species showed a positive relationship between mercury leveland body size. Natural dietary tracer, stable isotopes of nitrogen also showed that Hg levels in fishtissues were positively associated with trophic position. Our findings in this study not only added to3