Freshwater ecosystems constitute only a small fraction of the planet's water resources, yet support much of its diversity, with freshwater fish accounting for more species than birds, mammals, amphibians or reptiles. Fresh waters are, however, particularly vulnerable to anthropogenic impacts, including habitat loss, climate and land use change, pollution and biological invasions. This environmental degradation, combined with unprecedented rates of biodiversity change, highlights the importance of robust and replicable programmes to monitor freshwater fish. Such monitoring programmes can have diverse aims, including confirming the presence of a single species (e.g., early detection of alien species), tracking changes in the abundance of threatened species, or documenting long‐term temporal changes in entire communities. Irrespective of their motivation, monitoring programmes are only fit for purpose if they have clearly articulated aims and collect data that can meet those aims. This review, therefore, highlights the importance of identifying the key aims in monitoring programmes and outlines the different methods of sampling freshwater fish that can be used to meet these aims. We emphasize that investigators must address issues around sampling design, statistical power, species’ detectability, taxonomy and ethics in their monitoring programmes. Additionally, programmes must ensure that high‐quality monitoring data are properly curated and deposited in repositories that will endure. Through fostering improved practice in freshwater fish monitoring, this review aims to help programmes improve understanding of the processes that shape the Earth's freshwater ecosystems and help protect these systems in face of rapid environmental change.

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Abstract– The age, growth and reproduction of Barbus bocagei sclateri (Günther, 1868) were studied from November 1987 to September 1989 in a tributary stream of the Guadalquivir River basin. The maximum ages observed were 8 + in males and 11 + in females. The seasonal growth began in April and lasted 4–6 months. The males matured during their third year of life (2 +) and females during their fifth/sixth year (4 +/5+). There was a significant difference in the overall sex ratio of 1. 3: 1 (961 males to 740 females). Reproductive activity started in April/May and lasted until June/July. The end of the reproduction period coincided with a fall in the percentage of oxygen saturation. During this reproductive period, females spawned 2 batches of eggs. The relationship between fecundity (Fec) and fork length (FL, mm) was: Fec= 7.54 × 10−4 FL3.06 The maximum contribution to the fecundity of the population was observed in the 6 + female group. The reproductive effort was also maximum in this age. Compared with the rest of the European barbel populations studied, the life‐history patterns of this stock are characterized by low annual growth, early maturity, reduced longevity and high fecundity.

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