The human impact on the distribution of aquatic species may well have started much earlier, maybe during the times of the great geographical discoveries. Opportunistic species, resistant

to low oxygen concentrations, such as L. hoffmeisteri, L. udekemianus and Tubifex tubifex could have been transported between continents in the past. Perhaps their recent cosmopolitan distribution is a result of human shipping activities over a period of several centuries. “
“Although brown-coloured cod have been known to occur sporadically in the North Sea and anecdotally referred to by local fishermen, the authors were unable to find any scientific publications relating to it. This lack of publications on this unique colouration in the cod prompted the authors to communicate this finding. On 22 June 2011, one specimen of cod with a unique brown coloration was caught in the North Sea at a depth of 18 m (GPS: 56°45,00′N; 007°24,50′E). Selleck Vemurafenib This specimen was a female with a total length of 442 mm and a mass of 1074.3 g. To estimate its age, sagittal otoliths

were prepared according to the procedure described by Secor et al. (1992). Samples were examined under a light microscope by two researchers independently, who were unaware of the fish’s size at the time of the examinations. The fish was aged as 2 years old. According to Ursin (1984) and Thorsen et al. (2010) cod fish from the North Sea reach a length between 356 and 412 mm at the age of 2 years, whereas in the first year of life they reach a length of 150 mm. This brown cod was longer at the same age than normally coloured click here cod fish from this location. The differences in the growth rates of cod have been found to be affected by differences in water temperature among the various catching areas, food quality and availability, and other factors that have been difficult to quantify in population studies

of this species (Brander 1995). Macroscopic and histological analysis of the gonads (after the method described by Vitale et al. 2006) showed that this female brown cod Casein kinase 1 was sexually immature with small oocytes containing a dense basophilic cytoplasm, a central nucleus with a few large nucleoli around its edge. In the North Sea, cod fish usually reach sexual maturity at the age of 5–6 years (Oosthuizen and Daan, 1974 and Rijnsdorp et al., 1991). According to Vitale et al. (2006) only 24 to 39% fish in age class 2 are mature. This ‘brown’ fish had its dorsal surface coloured dark brown to red with sides slightly brighter but still of an intensive brown colour; the ventral surface was bright but not white. The dorsal surface, top of the head and sides of the body were covered with many dark spots. The fins were dark brownish-red in colour and the first rays of the pectoral fins were intensively red. The iris was gold-coloured (see Figure 1).