The present study describes the annual condition as well the length-weight (LWR) and length-length relationships (LLR) of the Asian striped catfish, Mystus vittatus (Bloch, 1794) (Siluriformes: Bagridae), an important fishery in the Mathabhanga River (SW Bangladesh). A total of 2438 specimens (3.60-9.60 cm standard length) used in this study was caught with traditional fishing gear from January to December 2004. Overall, the allometric coefficient b of the LWR was close to the isometric value (b ¼ 3.058), although it suggested negative allometric growth for males (b ¼ 2.959) whilst positive allometric growth for females (b ¼ 3.134). The results further indicated that the LLRs were highly correlated (r 2 > 0.989, P < 0.001). The monthly gonadosomatic index showed that the reproductive period of M. vittatus began in April, and ended in August when the highest values of the Fulton's condition factor (K) indicated their recovery. These results will be useful for fishery managers to impose adequate regulations for sustainable fishery management not only in the Mathabhanga River of Bangladesh but also in neighbouring countries.
The present study describes the length-weight (LWR) and length-length (LLR) relationships for eight important small indigenous fish species (SIS) from the Mathabhanga River, southwestern Bangladesh, namely Amblypharyngodon mola
The feeding ecology of the exotic invasive black bullhead Ameiurus melas was conducted in the Iberian Peninsula for the first time. Dietary analysis based on the stomach contents of individuals caught in several Iberian basins was carried out as a first step to evaluate its potential threat for the native Iberian ichthyofauna. Aquatic macroinvertebrates (mainly Chironomidae) dominated the black bullhead's diet in all size-classes and sites, irrespective of natural riverine or artificial lentic habitats. Secondary prey items were responsible for the observed between-sites (microcrustaceans in artificial lentic habitat; oligochaeta and caddisfly larvae in natural riverine habitats) and ontogenetic diet differences (from microcrustaceans to larger prey). These diet variations were also detected in trophic diversity values and feeding strategy plots. Black bullheads consumed plant material, terrestrial prey and co-occurring fish species (native or exotic) and thus they could be considered as generalist or opportunistic, foraging on the most abundant and available prey. There was no positive relationship between black bullhead size (total length) and fish prey size, probably indicating piscivory on dead or dying vulnerable fishes as well as predation on smaller-sized active fishes. The results showed that the black bullhead could negatively affect native Iberian ichthyofauna throughout direct predation and competition. Aspects of potential conservation and management implications of fishes resulting from the undesirable presence of the black bullhead in Iberian water bodies are discussed.
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