International Journal of Aquaculture, 2024, Vol.14, No.3, 139-153 http://www.aquapublisher.com/index.php/ija 144 pollution level of their habitats. (D) CYP1A activity and pollution correlation: This shows the negative correlation between the maximum CYP1A activity of populations and their sensitivity to PCB126. (E) Variation in CYP1A activity: This shows the variation in PCB126-induced CYP1A activity among individuals and populations. Overall, Figure 1 demonstrates the differences in pollution resistance among F. grandis populations at different pollution levels and reveals the correlation between these differences and the inducibility of CYP1A enzyme activity (Adapted from Oziolor et al., 2019). Figure 1 Variation in sensitivity to pollution among F. grandis populations distributed along a steep pollution gradient in Galveston Bay (USA) (Adopted from Oziolor et al., 2019) Image caption: (A)Pollution gradient is scaled by color, from low (blue) to high (black). Populations include resistant (black, R1 to R3), intermediate-high resistance (red, IH1 to IH3), intermediate-low resistance (gold, IL1 to IL3), and sensitive (blue, S1 to S3). Genomics data were collected for populations denoted with circles. (B) Population variation in cardiac deformities in embryos exposed to PCB126 (error bars indicate standard error of the mean). Population variation in sensitivity to PCB-induced cardiac deformities [log median effective concentration (EC50)] correlates with (C) habitat pollution and (D) AHR pathway inducibility (CYP1A activation by PCB126). (E) PCB-induced CYP1A activity varies among individuals and populations (Adopted from Oziolor et al., 2019). 5.3 Habitat complexity and availability Habitat complexity and availability are vital for the survival and adaptation of aquatic species. The structural characteristics of aquatic habitats, such as the presence of vegetation, substrate type, and water flow, influence the ecological niches available to species and their adaptive strategies. Aquatic insects, for example, exhibit various adaptations to different water flow regimes in streams. Species adapted to high-velocity riffles and low-velocity pools show distinct morphological and behavioral traits that enable them to cope with the specific challenges of their habitats. These adaptations include changes in body shape and drifting behavior, which are crucial for maintaining position and accessing resources in flowing water (Mazzucco et al., 2015). The availability of suitable habitats is also influenced by human activities, such as habitat destruction and pollution, which can reduce the complexity and quality of aquatic environments. Conservation efforts must consider these factors to preserve the adaptive potential and biodiversity of aquatic species. 6 Case Studies of Adaptation in Aquatic Species 6.1 Adaptation in marine species The study of adaptation in aquatic species provides valuable insights into how organisms adjust to their environments through a combination of phenotypic plasticity, genetic evolution, and molecular mechanisms. This
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