Seeing red: color vision in the largemouth bass

Polyphenisms and polymorphisms: Genetic variation in plasticity and color variation within and among bluefin killifish populations

The presence of stable color polymorphisms within populations begs the question of how genetic variation is maintained. Consistent variation among populations in coloration, especially when correlated with environmental variation, raises questions about whether environmental conditions affect either the fulcrum of those balanced polymorphisms, the plastic expression of coloration, or both. Color patterns in male bluefin killifish provoke both types of questions. Red and yellow morphs are common in all populations. Blue males are more common in tannin-stained swamps relative to clear springs. Here, we combined crosses with a manipulation of light to explore how genetic variation and phenotypic plasticity shape these patterns. We found that the variation in coloration is attributable mainly to two axes of variation: (1) a red-yellow axis with yellow being dominant to red, and (2) a blue axis that can override red-yellow and is controlled by genetics, phenotypic plasticity, and genetic variation for phenotypic plasticity. The variation among populations in plasticity suggests it is adaptive in some populations but not others. The variation among sires in plasticity within the swamp population suggests balancing selection may be acting not only on the red-yellow polymorphism but also on plasticity for blue coloration.

Correlation between Feeding Behaviors and Retinal Photoreceptor Cells of Largemouth Bass, Micropterus salmoides, in Korea

The largemouth bass (Micropterus salmoides), a food resource in Korea, is a highly voracious predator, designated as an invasive species. It is both diurnal and nocturnal, with high adaptability and reproducibility. Since the predation characteristics are associated with sensitive dynamic visual acuity, we examined the ocular structure of the largemouth bass to investigate the association between photoreceptor cells and feeding behavior. Furthermore, the comparison of the prey-tracking ability of M. salmoides with that of other predatory fish (Coreoperca herzi and Lepomis macrochirus) with similar ecological characteristics revealed the structure and arrangement of photoreceptor cells, typical of a predatory fish in M. salmoides. The double and single cone cells in the retina were present in the regular mosaic patterns of the quadrilateral units, with four double cone cells surrounding a single cone cell. The photoreceptor cells, i.e., the rod, single, and double cone cells of M. salmoides, were smaller (2.3 ± 0.2, 3.82 ± 0.2, and 7.5 ± 0.2 μm, respectively) than those of other species (3.1 ± 0.24, 6.6 ± 0.5, and 11.3 ± 0.4 μm in diameter, respectively, in C. herzi). A smaller diameter of cone cells allows for a high-density arrangement of visual cells, possibly affecting the dynamic visual acuity for prey tracking.

Anatomy, ultrastructure and histology of the olfactory organ of the largemouth bass Micropterus salmoides, Centrarchidae

The detailed anatomy, ultrastructure and histology of the olfactory organ of Micropterus salmoides were investigated by a stereo microscope, a light microscope, and a scanning electron microscope. Its external structure shows a tube-like anterior nostril to stick out and a posterior nostril flat to the skin surface. Meanwhile, its internal structure, the olfactory chamber, contains a fan-shaped rosette structure with 9 to 11 lamellae in adult fish over 35 cm in standard length (SL) and two accessory nasal sacs (ethmoidal and lacrimal sacs) were found. Interestingly, the rosette in young fish under 15 cm in SL was a longitudinal structure in parallel with each of 4–5 lamellae. Histologically, the sensory epithelium (SE) on the olfactory chamber consists of 5 types of cells: olfactory receptor neurons, supporting cells, basal cells, lymphatic cells and mucous cells. In contrast, the non-sensory epithelium (NSE) has stratified epithelial cells, lymphatic cells and mucous cells. The mucous cells of the SE are abundant and distributed densely in one row on the outermost superficial surface, but the one of the NSE are less than the SE. From these results, the olfactory characters of M. salmoides may be related with its ecological habit spending in the middle layer of stagnant water contaminated, more or less.

Color preferences affect learning in zebrafish, Danio rerio

Animals may exhibit preference for colors that match their environment or the resources in the environment. These preferences may impact ability to learn associations with these colors and revert the associations when the reward contingency is modified. We used zebrafish Danio rerio from four populations to test if color preferences impact associative and reversal learning ability. First, we tested if preference for blue or green impact associative ability. We subjected individual fish through eight trials to associate a social stimulus with blue or green. Next, we tested if preference for red or green impact associative reversal learning ability. We trained fish in groups of three to associate a social stimulus with red or green over three trials, and reversed the reward contingency during the following session. Results showed that zebrafish preferred green over blue and domesticated fish chose green more than blue when there was a reward attached. Zebrafish also preferred red over green. Fish from one wild population learned with both colors and reversed learning only from green to red and not vice-versa. Fish from another population showed an overwhelming preference for red irrespective of what was rewarded. Domesticated fish did not show reversal learning ability.

Plasticity of opsin gene expression in the adult red shiner (Cyprinella lutrensis) in response to turbid habitats

Vision is very important to fish as it is required for foraging food, fighting competitors, fleeing from predators, and finding potential mates. Vertebrates express opsin genes in photoreceptor cells to receive visual signals, and the variety of light levels in aquatic habits has driven fish to evolve multiple opsin genes with expression profiles that are highly plastic. In this study, red shiners (Cyprinella lutrensis) were exposed to four water turbidity treatments and their opsin genes were cloned to elucidate how opsin gene expression could be modulated by ambient light conditions. Opsin gene cloning revealed that these fish have single RH1, SWS1, SWS2 and LWS genes and two RH2 genes. Phylogenetic analysis also indicated that these two RH2 opsin genes-RH2A and RH2B -are in-paralogous. Using quantitative PCR, we found evidence that opsin expression is plastic in adults. Elevated proportional expression of LWS in the cone under ambient light and turbid treatment indicated that the red shiner's visual spectrum displays a red shift in response to increased turbidity.