The effect of environmental colour on the growth, metabolism, physiology and skin pigmentation of the carnivorous freshwater catfish Lophiosilurus alexandri

Background color matching influences sexual behavior, growth, and mortality rate in an African cichlid fish

Phenotypic plasticity allows organisms to adapt to changing environments within their lifetimes. The cost of plastic adaptations may constrain the persistence of plasticity over evolutionary time. One potential cost is the possibility that phenotypic adjustment to specific environments can cause correlated responses that are not necessarily adaptive. Males in the African cichlid Astatotilapia burtoni are blue or yellow, and males are able adjust their body coloration to the color of the background, presumably to increase crypsis. To test whether background color influences fitness-related traits, we raised mix-sex groups of juvenile A. burtoni to adulthood in yellow or blue tanks. We found that fish in blue tanks were darker and more bluish, whereas fish reared in yellow tanks were paler and more yellow in body coloration. Males, but not females, from blue tanks showed earlier sexual maturation than those held in yellow tanks. However, across the duration of the experiment, there was a higher frequency of females mouthbrooding in groups housed in yellow tanks than those that were housed in blue tanks. In addition, fish in blue tanks exhibited reduced growth rate but higher survivorship relative to their yellow-reared counterparts. Our data suggests that background color affects important fitness-related traits in a color polymorphic cichlid, which may influence the evolution of phenotypic plasticity.

Effects of monochromatic lights on the melanophores arrangement in the spotted snakehead fish Channa punctata (Bloch, 1793)

Some freshwater teleost fish have pigment cells whose arrangement and shape are affected by the environment. Natural light has a wide range of light intensity. Fish are sensitive to the background and exposed light colour. Fish body colour is a significant criterion in fixing its market value, whether it is ornamental or edible. By favourable light exposure, a culturist may get a good market value of fish on most ethical grounds. In this study, we recorded the changes in melanophore response with the changes in light colour on Channa punctata. Adult fish were treated with monochromatic lights (darkness, white, blue and red light) for 5 and 28 days. After treatment, their body colour and melanophore size, number, length and the number of dendrites were studied. The results showed a significant influence of monochromatic light on melanophore arrangement in fish skin. The data showed that blue light is appropriate for the overall species colour of photic C. punctata. Continuous black or white light caused severe damage to the fish's appearance.

Impact of background colorations on growth, movement behavior, and some body physiological factors of Nile tilapia, Oreochromis niloticus

This study tested the reverence of background color with growth, movement behavior, and some body physiological factors in Nile tilapia. Fish were first acclimatized for two weeks in 80 L glass aquaria. In the experimental design, three groups were maintained separately. In 1st group, glass aquaria were covered with black, 2nd with green charts, and 3rd remained uncovered and maintained as a control group. All groups were in three replicates and fed on a 30% protein diet. All fishes were closely observed for movement behavior and growth-related parameters. On the 28th day, fish were anesthetized and blood was drawn from the caudal fin to determine some hematological parameters, cortisol, and glucose level. The highest weight gain and the greatest number of movements throughout the aquarium were observed in the control group. Furthermore, aquarium color determined the body pigmentation color. Black aquarium had the lowest weight gain, glucose level, FCR, DFI, FCE, and CF, while green aquarium had the highest cortisol level. Histological changes observed in black aquaria fish included reduced lamellar size, deformed blood vessels, and cardiac muscle fascicle in the gills, liver, and heart, respectively, while green aquaria fish showed fused lamellae, necrosis, fibrosis, endomiocardiac hyperplasia, and cardiac muscle fascicle. It was concluded that background coloration has a significant effect on the growth performance, behavior, hematology, body color, histology, cortisol, and glucose levels of Oreochromis niloticus, with green background inducing significant stress while black background causes black pigmentation with less growth.

Neuronal responses of melanin-concentrating hormone and corticotropin-releasing hormone to background color in the self-fertilizing fish, Kryptolebias marmoratus

We examined neuronal responses of hypothalamic melanin-concentrating hormone (MCH) and corticotropin-releasing hormone (CRH) to background color in the self-fertilizing fish, Kryptolebias marmoratus. Fish were individually reared in lidless white or black cylindrical plastic containers for 15 days. The number of MCH-immunoreactive (ir) cell bodies in the nucleus lateralis tuberis (NLT) of the hypothalamus was significantly greater in the white-acclimated fish, while no significant differences were observed in the nucleus anterior tuberis (NAT) of the hypothalamus. Significant differences were not seen in the number of CRH-ir cell bodies in the NLT between the groups. The body of the white- and black-acclimated fish appeared lighter and darker, respectively, compared with the baseline color. In the black-acclimated fish, feeding activity was significantly greater with a tendency toward higher specific growth rate compared with the observations in white-acclimated fish. No significant inter-group cortisol level differences were observed. These results indicate that background color affects MCH neuronal activity in the NLT as well as body color adaptation but does not affect CRH neuronal activity in K. marmoratus.

EFFECTS OF PERIODIC SALINITY VARIATION ON THE EXPRESSION OF SOME PHENOTYPIC TRAITS IN STRIPPED DWARF CATFISH (Mystus vittatus)

Salinity fluctuations are known to have direct or indirect influence on phenotypes and thereby, evolve the subsequent life history traits in aquatic animals especially in fish. The present study was carried out to investigate whether periodic salinity fluctuations can influence the expression of some phenotypic traits (e.g. survival, standard length, tail length, body area, and body colour) in stripped dwarf catfish (Mystus vittatus). Ninety medium sized stripped dwarf catfish were collected and reared up to three months dividing into two treatments such as control treatment (CT) and salinity treatment (ST). The CT fish were reared at 0 ppt during the experimental period, while ST fish were reared at 10 ppt in first month, 0 ppt in second month and 10 ppt again in third month. There were significant effects of salinity on survival and the overall body colour of stripped dwarf catfish during the experiment. The results showed a significant difference in the tail length between the two treatments in which the average of tail length with the ST throughout the experimental period was significantly smaller than the CT. The study also found that the ST fish were significantly less bright and highly fade in appearance compared to the CT fish. The overall results have revealed an important role of periodic salinity fluctuation on the expression of some phenotypic traits in stripped dwarf catfish and thereby, underpinned the evolution of different phenotypic traits in many animals and also their plasticity as result of environmental stress in nature. Keywords: Catfish, salinity stress, fish phenotypes, fish colour.

Lophiosilurus alexandri, a sedentary bottom fish, adjusts its physiological parameters to survive in hypoxia condition

We investigated blood gas, hematological and biochemical parameters, and gill morphology of Lophiosilurus alexandri juveniles submitted to hypoxia for 48 h, followed by recovery for 48 h. A total of 48 juveniles (360.0 ± 141.6 g) were distributed among eight tanks (120 L) and subjected to hypoxia condition (water with dissolved oxygen at 2.12 ± 0.90 mg L^-1) or normoxia (at 5.60 ± 0.31 mg L^-1). Blood gas values (pH, PvCO₂, PvO₂, sO₂, HCO₃^-, stHCO₃^-, and base excess) in hypoxia were significantly different from normoxia, while for lactate and the electrolytes (K⁺, Na⁺, Cl^-, and Ca²⁺) there was no significant change among treatments. The erythrocytes differed significantly between normoxia and hypoxia at 72 h (24 h of recovery), while for hemoglobin and hematocrit there were no significant differences. There was a significant difference in glucose, triglycerides, and cholesterol for both normoxia and hypoxia, while plasma protein remained unchanged. All gill components (epithelial cells, erythrocytes, pillar cells, mucous cells, ionocytes, undifferentiated cells, and blood capillary lumen) differed significantly between normoxia and hypoxia. A reduction in the length of the primary lamella was observed in the hypoxia and recovery treatments, when compared to normoxia. The secondary branchial lamella showed no significant difference for both treatments. Juveniles of Lophiosilurus alexandri adapted well to hypoxia for 48 h, as they were able to adjust most of their physiological variables to survive this stress condition. After 48 h of hypoxia recovery, fish showed parameters similar to animals in normoxia. Thus, the present study shows that the tolerance to hypoxia conditions of L. alexandri, together with other important beneficial characteristics of the species, such as the high meat quality and high commercial value, demonstrates its great potential for production among regional species.

Fish skin pigmentation in aquaculture: The influence of rearing conditions and its neuroendocrine regulation

Skin pigmentation pattern is a species-specific characteristic that depends on the number and the spatial combination of several types of chromatophores. This feature can change during life, for example in the metamorphosis or reproductive cycle, or as a response to biotic and/or abiotic environmental cues (nutrition, UV incidence, surrounding luminosity, and social interactions). Fish skin pigmentation is one of the most important quality criteria dictating the market value of both aquaculture and ornamental species because it serves as an external signal to infer its welfare and the culture conditions used. For that reason, several studies have been conducted aiming to understand the mechanisms underlying fish pigmentation as well as the influence exerted by rearing conditions. In this context, the present review focuses on the current knowledge on endocrine regulation of fish pigmentation as well as on the aquaculture conditions affecting skin coloration. Available information on Iberoamerican fish species cultured is presented.

Universal model for the skin colouration patterns of neotropical catfishes of the genus Pseudoplatystoma

Fish skin colouration has been widely studied because it involves a variety of processes that are important to the broad field of the developmental biology. Mathematical modelling of fish skin patterning first predicted the existence of morphogens and helped to elucidate the mechanisms of pattern formation. The catfishes of the genus Pseudoplatystoma offer a good biological study model, since its species exhibit the most spectacular and amazing variations of colour patterns on the skin. They present labyrinths, closed loops (or cells), alternate spots and stripes, only spots and combinations of these. We have extended a well known mathematical model to study the skin of Pseudoplatystoma. The basic model is a two component, non-linear reaction diffusion system that presents a richness of bifurcations. The extended model assumes that there are two interacting cell/tissue layers in which morphogens diffuse and interact giving rise to the skin colouration pattern. We have found that by varying only two parameters we are able to accurately reproduce the distinct patterns found in all species of Pseudoplatystoma. The histological analysis of skin samples of two species of this genus, with different patterns, revealed differences on the disposition of the colouration cells that are consistent with our theoretical predictions.

Accidentally catching of the catfish Lophiosilurus alexandri (Steindachner, 1876) larvae in aquariums with different colors

The aim of this study was to evaluate the effect of different colors in development and survival of catfish Lophiosilurus alexandri larvae, as well as over the visual ability of the handler. Larvae were placed in 5 L-aquariums at a density of 7 larvae L-1 , and aquariums had different colors, and were: green and blue (light colors); brown and black (dark colors). The final development; survival, total and standard length, weight and biomass of the larvae were similar in all colored aquaria. The highest mortality occurred during the first days after hatching, declining over the period, when it is observed the larval development, indicating that care should be necessary in the first few days. During cleaning handling, the accidental catch of larvae was higher in black aquariums. In the first days of life, due to the fragility of the larvae, it is possible to verify that between the second and third day occur the greatest mortalities. The number of accidentally captured larvae was lower than the mortality, suggesting that the high mortality in early larval life is not influenced by the handler management. The catfish L. alexandri larvae should be cultivated in aquariums that allow a good contrast between the larvae and the background, to avoid accidental capture of larvae by the handler. It is suggested to avoid the use of dark and black aquariums.

Daily rhythms of leukocytes populations, biochemical and enzymatic blood parameters in a carnivorous freshwater catfish (Lophiosilurus alexandri)

The aim of this study was to investigate the daily rhythms of hematological, biochemical and enzymatic parameters of the blood of a nocturnal model of fish (Lophiosilurus alexandri) bred in the laboratory (F1). Thirty-six juveniles were stocked in six tanks of a recirculation aquaculture system for 20 days. The fish were exposed to a light:dark cycle of 12:12 h and were fed 1% of biomass twice a day with commercial diet. The daily rhythms of hematological, biochemical and enzymatic parameters were then measured at six sampling times "zeitgeber time = ZT" at four-hour intervals under light:dark 12:12 h (lights on = ZT0, at 8.00 a.m). No differences were observed to alkaline phosphatase, glucose, cortisol, aspartate aminotransferase, superoxide dismutase, total protein and hematocrit (p > 0.05). However, white blood cell count, Lymphocytes (LYN), Neutrophils (NEU), Eosinophil and Neutrophils to Lymphocytes ratio were significant different between sample times (p < 0.05). Also, a significant difference in alanine transaminase was observed, with a peak of production at nighttime. In contrast, glutathione peroxidase peaked at 8:00. Uric acid, magnesium and Calcium (Ca⁺⁺) showed statistically significant differences (p < 0.05). A significant difference was observed (p < 0.05), with a peak of albumin at 08:00 and triglycerides at 12:00, while cholesterol was low (p < 0.05) at 08:00 and higher from 12:00 to 04:00. Cosinor analysis revealed also rhythmicity to SOD, UA, Mg and Ca⁺⁺, ALB and CHO (p < 0.05). In conclusion, the time of day must be considered a key factor when using blood parameters as biomarkers for disease, health and welfare in the L. alexandri aquaculture.

Comparative Performance Analysis of Support Vector Machine, Random Forest, Logistic Regression and k-Nearest Neighbours in Rainbow Trout (Oncorhynchus Mykiss) Classification Using Image-Based Features

The main aim of this study was to develop a new objective method for evaluating the impacts of different diets on the live fish skin using image-based features. In total, one-hundred and sixty rainbow trout (Oncorhynchus mykiss) were fed either a fish-meal based diet (80 fish) or a 100% plant-based diet (80 fish) and photographed using consumer-grade digital camera. Twenty-three colour features and four texture features were extracted. Four different classification methods were used to evaluate fish diets including Random forest (RF), Support vector machine (SVM), Logistic regression (LR) and k-Nearest neighbours (k-NN). The SVM with radial based kernel provided the best classifier with correct classification rate (CCR) of 82% and Kappa coefficient of 0.65. Although the both LR and RF methods were less accurate than SVM, they achieved good classification with CCR 75% and 70% respectively. The k-NN was the least accurate (40%) classification model. Overall, it can be concluded that consumer-grade digital cameras could be employed as the fast, accurate and non-invasive sensor for classifying rainbow trout based on their diets. Furthermore, these was a close association between image-based features and fish diet received during cultivation. These procedures can be used as non-invasive, accurate and precise approaches for monitoring fish status during the cultivation by evaluating diet's effects on fish skin.