Fernando Mayer Pelicice

The use of freshwater fish as biological control agents has been widely implemented to manage populations of perceived nuisance species, ranging from disease vectors to aquatic weeds. While these introductions are often intended as a management tool, they can have unintended and severe ecological, economic, and social consequences. This review assesses the risks associated with using non‐native fish for biological control, emphasising the challenges presented by their persistence, adaptability, and interactions with native species and ecosystems. Key case studies illustrate how species such as mosquitofishes ( Gambusia spp.), grass carp ( Ctenopharyngodon idella ), and tilapias (mainly Oreochromis spp.) have inadvertently contributed to biodiversity loss, habitat degradation, trophic disruptions, and disease transmission, while often failing to effectively control the target species. We further explore the limitations of biocontrol strategies, including the context‐dependent nature of species interactions and deferred negative impacts. Given the complexity and unpredictability of biological control interventions, rigorous impact assessments and long‐term monitoring programmes are needed before and after introducing non‐native fish as control agents, embedded within an adaptive management framework that allows for responsive decision‐making based on observed ecological outcomes. Precautionary policies should prioritise habitat restoration and native species‐based solutions over the introduction of non‐native species to support more sustainable and ecologically responsible management decisions.

Neotropical cichlids are characterized by spectacular color diversity, but some groups remain poorly investigated. In this context, the present study characterized color traits in peacock basses ( Cichla kelberi and C. piquiti ) from the Middle Tocantins River (Brazil), and investigated the link with biological (development, sex, reproduction) and environmental drivers (feeding and water transparency). Both species showed striking polychromatism, but with some conspicuous patterns. For C. kelberi , immature and non-reproductive individuals were associated with melanistic patterns and the absence of spots, with either conspicuous or opaque vertical bars. Adults in reproduction, on the other hand, were associated with yellow body, spots in the fins, and dorsal blotches. For C. piquiti , immature and non-reproductive individuals showed a wide range of color patterns, but associated with non-blue tints. Immature fish, in particular, had spots in the body and head, and a red caudal fin. Reproductive fish were associated with blue hues, the absence of spots and a non-red caudal lobe. For both species, color variation was not associated with feeding, sex and water transparency. Our findings indicate that coloration represents transient (but stable) phenotypic states subjected to unidirectional or cyclical changes, supporting the hypothesis that growth and reproduction drive color variation in Cichla .

Fish stocking is a popular tool used to manage fishery stocks and wildlife. However, the overall contribution of this technique to enhance or rehabilitate natural populations has been criticised, because of technical issues, inherent limitations and abuses. Multiple factors may affect the outcome of stocking, and a primary assumption is environmental feasibility, i.e., whether the action has the potential to generate positive effects in a specific scenario. To shed light on this important issue, our essay presents a theoretical and accessible framework to define the environmental feasibility of fish stocking applied to management systems associated with population enhancement, rehabilitation, or restoration. Our framework builds on the main concepts and theories of population ecology, particularly ecological carrying capacity ( K ), specific stressors, population size ( N ) and growth. Considering that feasibility is controlled by (i) the ratio N/K , (ii) population and environmental constraints and (iii) the possibility of natural recovery, we developed a simple equation to describe the relationship among these variables, and built scenarios and numerical simulations to illustrate how feasibility responds to different contexts. The framework shows that feasibility is highly sensitive to environmental settings, with potential application restricted to specific scenarios, which may explain why many actions have contributed little or nothing to the rehabilitation or conservation of populations in the real world. The proposed framework is simplistic and has no applied ambition, but intends to inform scientists, managers and authorities about critical aspects that constrain fish stocking, supporting a much‐needed debate about the uncritical use of management tools.

The central nervous system (CNS), composed of the encephalon and spinal cord, regulates physiological, motor, and cognitive processes in vertebrates. In Neotropical fishes, however, encephalon morphology and size remain poorly studied, particularly in cichlids. This study describes the encephalon of Cichla piquiti, analyzing variations across developmental stages, sex, and native vs. invasive populations. The relative proportions of brain structures were distinct, with a marked dominance of the tectum mesencephali (54–58%), highlighting strong reliance on visual information. No sexual dimorphism was detected, suggesting similar behavioral patterns between males and females. Juveniles and adults differed in the shape of the telencephalon, lobus inferior hypothalami, and cerebellum, reflecting developmental adjustments in response to sensory and ecological demands. Morphology also varied between populations: juveniles from the native Tocantins population showed faster growth of major brain regions, whereas invasive individuals from Furnas exhibited delayed development, likely associated with contrasting environmental pressures. The encephalization quotient (EQ) exceeded 1, surpassing typical values reported for Actinopterygii, and the telencephalon and tectum mesencephali accounted for half of the brain volume, suggesting enhanced cognitive abilities. This work provides the first detailed anatomical account of Cichla brain morphology, offering insights into cognitive potential, phenotypic plasticity, and mechanisms underlying the species’ invasive success.

Insetos aquáticos representam cerca de 3% da diversidade de Hexapoda, constituindo 90% da fauna de ambientes dulcícola. Além de serem fundamentais para as cadeias tróficas, são utilizados como excelentes bioindicadores de ambientes aquáticos. O ribeirão São João tem um papel fundamental para o município de Porto Nacional, fornecendo água para a população local e moradores da região rural que utilizam essa fonte para irrigação de lavouras. No entanto, a biodiversidade aquática dessa drenagem permanece desconhecida. Este trabalho fornece informações inéditas da entomofauna local, contribuindo com dados sobre a diversidade de insetos para o estado do Tocantins. Foi realizado um levantamento da fauna de insetos aquáticos abrangendo quatro períodos (início da seca, seca, início da chuva e cheia), com a finalidade de amostrar a riqueza de táxons do local. Portanto, o presente trabalho apresenta uma chave pictórica para identificação da entomofauna aquática e semiaquática do ribeirão São João (RSJ), Porto Nacional, na qual é constituída por uma riqueza de nove ordens (Coleoptera, Diptera, Ephemeroptera, Hemiptera, Lepidoptera, Megaloptera, Odonata, Plecoptera e Trichoptera) e 40 famílias.

Neotropical freshwater ecosystems harbor some of the world’s most diverse fish communities, playing a fundamental role in ecosystem functionality and providing essential and free services to human societies. However, this exceptional biodiversity faces escalating threats from multiple and widespread anthropogenic pressures, particularly small-scale engineering activities such as channelization, damming, road crossings, water extraction, and mining, which remain insufficiently assessed despite their cumulative and synergistic impacts. This Special Issue, Impacts of Small-Scale Engineering Projects on Neotropical Freshwater Fish Diversity compiles eleven studies to assess how small-scale interventions affect fish diversity and ecosystem processes. Collectively, these studies consistently demonstrate ecological trends including habitat simplification, loss of sensitive species, predominance of tolerant or generalist taxa, and disturbances on reproductive and trophic dynamics. Hydrological alterations and reduced habitat heterogeneity are key drivers of biotic homogenization and simplification of functional diversity. Overall, these publications emphasize that both local and regional disturbances synergistically compromise the structural and functional integrity of fish assemblages. Maintaining ecological connectivity and functional diversity is essential for maintaining integrity and resilience of Neotropical freshwater ecosystems, and findings underscore the urgent need to integrate small-scale impacts into basin management and conservation, recognizing their cumulative and often underestimated influence on biodiversity and ecosystem functioning.