Global trends, biases and gaps in the scientific literature about freshwater fish eggs and larvae

Abstract

Syntheses of knowledge are important to reveal trends, biases and gaps in the scientific literature, indicating main data shortfalls and research needs. In this regard, the authors conducted a broad systematic review on the literature about freshwater fish eggs and larvae to investigate (a) temporal trends in the global scientific production, (b) the scope and habitat types, (c) the spatial distribution of studies, (d) the fish species contemplated and their respective conservation status and (e) the factors associated with the spatial distribution of studies. They analysed 654 studies published between 1950 and 2020. The number of studies has increased over time, but with a weak trend. Most studies investigated basic questions about biology and ecology and were carried out chiefly in rivers and lakes. These studies covered 95 freshwater ecoregions (22.3% of all ecoregions) and recorded 871 fish species (4.8% of all freshwater fish currently described). Most species were assessed by the IUCN and classified into six threat categories, but approximately 35% were not evaluated. The main drivers affecting the spatial distribution of studies were ecoregion area, road density, river volume and the number of hydroelectric plants. Results point to significant biases and gaps in the global scientific literature on fish eggs and larvae, especially associated with habitat type, spatial distribution and target species, emphasizing the need to address specific topics. Such biases and gaps indicate the existence of important data shortfalls, which compromise management and conservation planning, as information on fish eggs and larvae is basic and critical for the assessment of fish recruitment and population dynamics.

Spatial and seasonal distribution of fish eggs and larvae in one free‐flowing river in the Neotropical savanna

“…This general model has explained the reproductive success and recruitment in different Neotropical basins that contain floodplains (Agostinho et al ., 2004; Jiménez‐Segura et al ., 2010; Rosa et al ., 2018). Nonetheless, important river basins in the region still lack an investigation into the patterns of reproduction of fish species, especially with regard to the ecological study of eggs and larvae (Carnicer et al ., 2023; Reynalte‐Tataje et al ., 2020). This is the case for river basins in savanna ecosystems.…”

Spawning cohort trade‐offs of reproductive time and output in cyprinid fish along an elevation gradient

“…Reduced spawning success alters fish recruitment and thus can lead to population declines and even ecosystem collapse (Wright & Trippel, 2009). Unfortunately, knowledge about how environmental variation affects fish spawning strategies and success is often quite limited (Carnicer et al., 2023). Spawning requirements and success can vary not only between different species but also among geographically separated populations within the same species (Teletchea et al., 2009).…”

All roads lead to… fish egg and larvae literature?

“…In this issue, Carnicer et al (2022) apply this thinking to the field of freshwater fish eggs and larvae by conducting a scientometric review on the scientific literature, analysing 654 studies published between 1950 and 2020, to identify global trends, biases and literature gaps. The results from their analysis are both illuminating and thought provoking and provide insights that are vital to improving the scientific literature.…”

“…It was found that most of the studies investigated basic questions on the biology and ecology of fish eggs and larvae such as environmental conditions, spawning areas and recruitment. Carnicer et al (2022) highlight that many of these studies had been published in low‐impact journals or remained in unpublished grey literature, with minimal impact, which could demonstrate the need for more novel hypothesis testing and experimental manipulation. Although basic research is an important first steppingstone, especially for the many data deficient fish species found globally.…”

“…Even if we could learn something from these cases, that knowledge could provide some, even if it is very small, amount of compensation. However, in the case of hydroelectric installations, not only are they detrimental to fish communities (Dadswell et al, 2018; Orsi and Britton, 2014; Twardek et al, 2021) but Carnicer et al (2022) state that hydropower companies often impose restrictions to data disclosure, with many results hidden in grey literature such as reports. All roads may therefore lead to more scientific literature and greater insights, but at what cost?…”