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Abstract Investigating the determinants of the reproductive biology of fishes is an essential component of fisheries research. Tilapia breeding patterns were investigated to determine the impact of non‐native Oreochromis niloticus on the native congeneric Oreochromis macrochir in the upper Kabompo River in the Northwest of Zambia using the gonadosomatic index and the sex ratios. Oreochromis niloticus was the most abundant fish caught (221, 63.5%) than O. macrochir (127, 36.5%). Results showed that the overall gonadosomatic index means of O. macrochir in both sections were similar. Oreochromis macrochir bred in December and February–March, with no reproduction in June. However, O. niloticus in the invaded section indicated all year reproduction through reduced spawning in May–June, with increased spawning activity in February–March. The sex ratio (females: males) was 1:1.3 and 1:1.7 for O. niloticus and O. macrochir, respectively, and both significantly deviated from the sex ratio of 1:1 (ꭓ2 = 8.42 and 9.37, p

Investigating the determinants of the reproductive biology of fishes is an essential component of fisheries research. Tilapia breeding patterns were investigated to determine the impact of non‐native Oreochromis niloticus on the native congeneric Oreochromis macrochir in the upper Kabompo River in the Northwest of Zambia using the gonadosomatic index and the sex ratios. Oreochromis niloticus was the most abundant fish caught (221, 63.5%) than O. macrochir (127, 36.5%). Results showed that the overall gonadosomatic index means of O. macrochir in both sections were similar. Oreochromis macrochir bred in December and February–March, with no reproduction in June. However, O. niloticus in the invaded section indicated all year reproduction through reduced spawning in May–June, with increased spawning activity in February–March. The sex ratio (females: males) was 1:1.3 and 1:1.7 for O. niloticus and O. macrochir, respectively, and both significantly deviated from the sex ratio of 1:1 (ꭓ2 = 8.42 and 9.37, p <.05). Our study has revealed that O. niloticus was able to spawn across all sampled months with a 23% higher breeding population than O. macrochir, which might explain the suppression in the abundance of native O. macrochir. Due to the superior breeding patterns of O. niloticus, fisheries, wildlife, and aquaculture practitioners need to make contingency plans to alleviate its impacts further downstream of the Kabompo River. [ABSTRACT FROM AUTHOR]

Martin J, Daverat F, Pécheyran C, Als TD, Feunteun E, Réveillac E. An otolith microchemistry study of possible relationships between the origins of leptocephali of European eels in the Sargasso Sea and the continental destinations and relative migration success of glass eels. Ecology of Freshwater Fish 2010: 19: 627-637. © 2010 John Wiley & Sons A/S Little is known about the extent to which Atlantic eels coming from different European rivers converge on the same spawning site. Our aim was to evaluate the spatial homogeneity of eel spawning area(s) with an otolith microchemistry approach. This work compared the elemental signatures of otolith's core region of Anguilla anguilla leptocephali caught in the Sargasso Sea in 2007 with those of glass eels and elvers sampled in European estuaries during 2006, 2008 and 2009. Using laser ablation inductively coupled plasma mass spectrometry, the same annular ablation trajectory along the first feeding mark was applied on otoliths of glass eels, elvers and leptocephali. The concentrations of thirteen isotopes in the otoliths of glass eels/elvers did not vary among three annual cohorts collected in eleven European locations. However, otolith elemental fingerprints of leptocephali differed significantly from glass eels otolith's signature. Although the mechanisms that regulate the differences in trace element signatures among leptocephali and glass eels/elvers are unknown, we propose that the sampled glass eels/elvers were born in a spawning site or region where favourable transport and/or feeding conditions occurred. Conversely, the leptocephali may have been sampled in a less favourable region in the Sargasso Sea, with a low probability of reaching continental growth areas. [ABSTRACT FROM AUTHOR]