Time lags associated with changes in stable isotope ratios are essential information for quantitatively analyzing shifts of food habits and habitats. To investigate time lags associated with fish growth in a natural setting, we monitored the change in δ15N in the muscle tissue of a fluviallacustrine amphidromous goby, Rhinogobius sp. (the orange form), in the Lake Biwa water system. Because δ15N is distinct between lacustrine and fluvial ecosystems, the δ15N of age-0+ fish drastically decreased after their upstream migration from the lake. About 80% of the change in δ15N was attributed to growth. Nitrogen was replaced at the rate of 520%·month1 by metabolic turnover. The half-change period for δ15N was estimated as being longer than 1 month with the contribution of growth and metabolic turnover in the field. These results from the field show that growth is primarily responsible for isotopic changes in fish muscle and highlight the need to examine the role of metabolic turnover using slow-growing fish.
Drosophila serrata is a member of the montium group, which contains more than 98 species and until recently was considered a subgroup within the melanogaster group. This Drosophila species is an emerging model system for evolutionary quantitative genetics and has been used in studies of species borders, clinal variation and sexual selection. Despite the importance of D. serrata as a model for evolutionary research, our poor understanding of its genome remains a significant limitation. Here, we provide a first-generation gene-based linkage map and a physical map for this species. Consistent with previous studies of other drosophilids we observed strong conservation of genes within chromosome arms homologous with D. melanogaster but major differences in within-arm synteny. These resources will be a useful complement to ongoing genome sequencing efforts and QTL mapping studies in this species.
Fluvial–lacustrine migrations of a landlocked goby, Rhinogobius sp. (the orange form) in the Lake Biwa water system were traced using stable nitrogen and carbon isotope ratios. The δ15N values of Rhinogobius sp. individuals in the lake were significantly higher than those of large individuals in a tributary river (≥1+ age) without overlap of the range, although there was little difference in the δ13C values between these two locations. Because these values reflected those of the corresponding prey organisms in either location, it was revealed that none of the large individuals had migrated from one location to the other. The δ15N values of the small individuals in the tributary river (0+ age) were too high to be fluvial residents. This result indicated that all of the small individuals studied had spent their larval periods in the lake, and that immigrant individuals can be distinguishable by measuring the δ15N values retaining the effect of foraging in the alternate location. We conclude that the δ15N value works as a useful tracer to clarify the fluvial–lacustrine migration pattern of the fish.
Catch per unit effort (CPUE) and species composition in the pair-trawl fishery in commercial Area A of southern Lake Malawi were assessed from 1991 to 2001. CPUE declined from 1.7 t day )1 in 1995 to 0.5 t day )1 in 2001 and the fishery is considered depleted. In 2000/2002, catch composition differed significantly from a 1991 survey, and was dominated by haplochromine cichlids (92% by weight). Of 98 haplochromine cichlid taxa identified in the catch, 18 contributed ‡1% by weight. The artisanal fishery targeted similar species of a similar size. It was recommended that: (1) renewed investment and increased effort in the pair-trawl fishery is not advisable; (2) there was a need for effort limitation in Area A and (3) the pair-trawl fishery should not be managed in isolation of the artisanal fishery.artisanal fishery, catch per unit effort, Lake Malawi, management policy, pair trawl.
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