Objective. Evaluate the effects of the habitat zone and sex on the serum biochemical and morphometric response of Ichthyoelephas humeralis in lotic ecosystems of Los Ríos province, Ecuador. Materials and methods. One of the native species (I. humeralis) that are most commercialized in the cantons of Quevedo, Mocache and Fumisa of Los Ríos Province was identified, 60 specimens were captured for each area (180 total), the sexed and the live weight, length, thickness of the head, body and tail were determined; condition Factor and blood biochemistry (glucose, cholesterol and triglycerides). Results. For the morphometric indicators there was no zone-sex interaction. There were only significant differences (p<0.05) for the effect of sex on live weight, length, thickness of the head, body and tail with the highest values ​​for males (284.98 g; 29.32 cm; 6.77 cm; 14.81 cm and 7.80 cm, respectively) except for the condition factor which did not differ statistically. For blood biochemistry the best results for glucose and triglycerides in Quevedo with 162 and 320.67 mg/dL, respectively while cholesterol was higher with 130 mg/dL for Fumisa. Conclusions. The effect of sex on morphometric indicators was evidenced, with the best results for males. While the blood biochemistry showed variability with respect to the areas with the highest results for Quevedo, due to fluctuations in natural conditions of the environment and food.

Currently, there are more than 34.725 species of fish that represent 50% of all species of vertebrates (1). South America is characterized by being the continent with the greatest diversity, approximately 8.000 registered species, but information on biology, ecology, morphometry, and biochemistry is scarce. In the Los Ríos province, in Ecuador, 951 species of freshwater fish have been identified, however, studies have focused on their registration, leaving other aspects like optimal range for the different stages and categories of morphometric and blood indicators fish unknown (2).

The bocachico (Ichthyoelephashumeralis) is one of the fish native species registered in Ecuador that lives in lotic ecosystems distributed from Colombia to Peru. It is a fish that can reach a live weight of 2.5 kg, and a length of 38.5 cm (3,4). Ovchynnyk (5) conducted the first studies on this and other native freshwater species in Ecuador reporting some biological aspects. Cadena (4), carried out a preliminary study regarding the length-weight relationship and stages of gonadal maturity of I. humeralis, determining that the total length fluctuates between 155 and 385 mm, while the weight varies between 49.7 and 883.5 g. The most advanced stages of sexual maturity were recorded from January to May and from July to August. Stewart et al (6), recorded 473 species and 225 genera, reporting 250 species, 100 genera and eight families for the first time in the Aguarico, Napo and Curaray affluents belonging to the Napo river system.

Florencio et al (7), carried out bioecological studies in the Abras de Mantequilla wetland using I. humeralis to study sexual maturity. Revelo and Elías (8) and Revelo (9) investigated some biological and fishing aspects of the main fish species in the water system of the Los Ríos province, determining the size range of Brycon alburnus, which was between 14 and 37 cm, while I. humeralis between 13 and 32 cm.

Recent studies have reported the characterization of morphological and meristic traits, performance, pulp parameters, and fatty acid composition in muscle tissue Cichlasoma festae comparing wild and cultivated conditions (10,11). Also, Rodríguez et al (12) studied the allometric relationship and growth models of Cichlasoma festae juveniles, obtaining growth models between length and weight, which would avoid stress due to fish handling and risks associated with pathologies.

González-Martínez et al (13) applied a multivariate analysis to characterize morphometric and meristic features of Dormitator latifrons, concluding that the morphological characteristics of this species are influenced by the production system, with the largest fish coming from fish farms where food availability is higher. Furthermore, in that study, sexual dimorphism was observed, although there were no large significant differences in morphometric measurements. Meristic counts had effect on the production system and sex, with small variation coefficients. These measurements are species-related and change very little.

Considering the above, there are few studies in .. humeralis, but morphometric and blood biochemistry information is still missing. Blood biochemical parameters in fish farming have proven to be a very useful tool to evaluate and monitor the health status of wild and captive organisms because they are species-specific and age-dependent physiological values. Several factors can cause temporary changes in the fish blood biochemistry, like the reproductive cycle, feeding, temperature, pH, and photoperiod. Biochemical tests provide 17 important indicators of metabolic disorders, deficiencies, and chronic stress before they present any clinical signs; so, it is important to know how these parameters can change over time (14).

Exogenous factors such as specimen handling, disease, and stress cause significant changes in the blood composition. Fluctuations in the concentration of cortisol, glucose and cholesterol have been detected due to manipulation and hypoxic stress (15). Some studies have been directed to determine hematocrits, hemoglobin, triglycerides, lymphocytes, monocytes, neutrophils, basophils, proteins, glucose, and leukocyte erythrocytes in some species like I. maculatum, S. minor and I. conceptionis (16); B. amazonicus (17) and A. ocellatus (18).

Physiological differences between gender are related to primary and secondary sexual characteristics and their adaptations, result of different strategies used for reproductive success, with marked differences in blood parameters between females and males due to a high metabolism in males. Although according to the report by Bastardo et al (19) that females have higher values in blood parameters. The variation of the results may be due to the different conditions in which the organisms were maintained in each study.

In this sense, it was indicated that age, sex, habitat, feeding, and migrations affect fish physiology, being able to affect the immune response and growth rate. It is also highlighted that fish are subject to overexploitation, and contamination of aquatic ecosystems because of urbanization, industrialization, indiscriminate use of chemicals in the agricultural sector, residues of agricultural inputs, vegetable and animal remains, to this are added the effects of climate change, and the increased presence of pathogens and diseases (20). The objective of this research was to evaluate the effects of habitat and gender on the morphometric and serum biochemical response of I. humeralis in lotic ecosystems of the Los Ríos province, Ecuador.

Sampling area. This research was carried out in three areas of the Los Ríos province, Fumisa, Camarones area at 0°43’16’ S and 79°27’ W, the Pajarito enclosure belonging to the Mocache canton 1°8’03.92’’ S, 79°29’07.8’’ W, and Quevedo, an affluent of the River 1°2’30 S and 79°28’30 W (Figure 1). The climatic conditions of each of the places are reported in Table 1.

Process. For this research, one of the native freshwater species (I. humeralis) that is most commercialized in the cantons of Quevedo, Mocache and Fumisa of the Los Ríos Province was studied. Sixty specimens were captured for each area (180 total), and gender was determined considering morphological characteristics (2,21).

Live weight and morphometric indicators. The fish were weighed individually on a digital scale ±0.01 g (PE 3600 Mettler-Toledo, Columbus, OH, USA), the length was determined with the help of a measuring tape (Truper, 3m-Fh, Distrito Federal, MX) from the tip of the mouth to the fin of the tail. A digital vernier caliper (GT-MA15 Gester, ±0.001 mm, Xiamen, CN) was used to measure the thickness of the head, body, and tail. The Condition Factor was determined according to the following formula: (live weight/total length.) × 100 (22).

Biochemistry in blood plasma. One mililiter of blood was extracted from the hemal arch by puncturing the caudal artery, using 3 mL syringes (Bio-In, Guayaquil, EC), then the samples were placed in capillary tubes (Isolab, Laborgeräte GmbH, Eschau, DE) with heparinized inner surfaces, then centrifuged (Gemmy, PLC-05, Taipei, TW) at 1200 rpm for 10 min to obtain serum plasma and subsequently quantified glucose, cholesterol and triglyceride using commercial kit reagents (Human liquicolor, Wiesbaden, DE), samples were incubated for 25 min at 37°C (23). Absorbance (ABS) readings were performed on a spectrophotometer (SunostIk, SBA-733 Plus, Kunshan Road, CHN) at 510 nm for glucose, and 500 nm for cholesterol and triglycerides. All analyzes were performed in triplicate.

Statistical design and analysis. A completely randomized design was used with a factorial arrangement (3×2), three habitat areas, and gender (female and male). Kolmogorov-Smirnov and Bartlett tests were applied to the data obtained. Subsequently, a double classification analysis of variance (ANOVA) was carried out considering the area of ​​habitat and gender as sources of variation. Tukey’s test was used for the difference between the means. Between the weight and size of the fish, a correlation was determined. All statistical processing (p≤0.05) were performed with the IBM SPSS statistical program. 22.0.

For gender (Table 2), a greater number of females were found in all the studied areas (Fumisa, Mocache and Quevedo) with increases of 20, 13.34, 40 percentage units and as an average for this research of 24.44% of females above in comparison of the males.

Regarding morphometric features (Table 3), there was no habitat-gender interaction, with greater variability for males. There were only significant differences (p<0.05) related to gender on weight, length, thickness of the head, body, and tail, with the highest values ​​for males (284.98 g; 29.32 cm; 6.77 cm; 14.81 cm and 7.80 cm, respectively) except for the Condition factor, which did not differ statistically (p>0.05). While for the inhabited areas, the condition factor showed differences with the best results (1.15) for Quevedo.

When analyzing the weight-length relationship, a correspondence between growth and weight was observed with adjustments of third-order polynomial equations for females in the three areas (Mocache, Fumisa and Quevedo) and R. values ​​higher than 0.64. Whereas third order polynomial equations were established for males in Fumisa and Quevedo and for Mocache Potential with R. above 0.70 (Figures 2, 3 and 4).

For blood biochemistry, no habitat-gender interaction was recorded, with the highest fluctuations according to minimum and maximum for males and only effects of the area with the highest results for glucose and triglycerides were observed in Quevedo with 162.00 and 320.67 mg/dL; while cholesterol was higher with 130.00 mg/dL for Fumisa, although without significant differences with the Quevedo area. In the case of gender, no significant differences were observed, but the results were numerically higher for females (Table 4).

The complexity and plasticity in fish reproductive biology determines a population structure in which gender proportion is not always 50/50 but depends on the resources allocation and natural selection (21). In studies of Colossoma macropomum, Pineda-Santis et al (24) reported proportions of 73.71% females and 26.09% males. Pacheco-Bedoya (25) and Álvarez-León (26) evaluated biological and fishing aspects of species captured in the Babahoyo river and an affluent of the Samborondón canton, finding different gender proportions, i.e., female-male percentages, for A. rivulatus (49.30-50.70%), H. microlepis (58.40-41.60%), I. humeralis (73.80-26.20%), and E. mutisii (61.40-38.60%) and 81.82-18.18% female-male rate for the Bogotá river. Gender variability could be given by the reproductive and spawning season, I. humeralis spawns in winter (December to March). Other factors like distribution, mortality, feeding, pH, and temperature of the water also affect gender proportion. Embryonic gonads, starting from a common rudiment, made up of somatic cells of the gonadal crest and gonadal primordial cells, can develop in two different adult organs, ovaries, or testes, affecting the demographic structure of the population (27).

To identify the gender of Cichlasoma festae based on morphometric variations, Vivas-Moreira et al. (28) captured 500 specimens (weight in 20-50 g) in the Daule Peripa reservoir and the Peripa, Toachi and Baba rivers. The authors did not find differences between the sampling areas, while the relationships between variables (weight, total length, and length of the head) and gender were high, with r = 0.90-0.94. This variability in morphometric indicators associated with gender is probably strongly related to defensive or survival strategies of the species. For example, larger and heavier females can harbor larger eggs and ensure a better defense when they are most vulnerable, such as during laying. Contrary to a smaller size in males, which could mean a lower energy investment in growth but an increase in mobility capacity. In addition, this condition increases the ability to locate females, ease of courtship and forced insemination.

Results of the morphometric indicators (Table 3) coincide with those obtained by Caez et al (29), when evaluating A. rivulatus in the Quevedo River under cultivation and wild conditions, where 52 fish were sampled for each of the production forms, reporting fish weight between 90-228 g, total length of 14.8-21.8 cm, and head length of 3.4-6.6 cm. Therefore, they have used morphological and meristic characteristics to identify adaptation processes in nature and cultivated populations of the same species (30).

Moreno et al (22) studied morphometric parameters of Eremophilusmutisii by sampling 33 specimens in the Bogotá River, of which 27 were female and 6 males, reported 222.7 and 181.1 g; 28.6 and 28.1 cm; 3.0 and 2.1 cm of body width; 3.2-3.1 and 0.9 and 0.8 of Condition Factor for females and males, respectively. With better performance from a numerical point of view for the females, results that differ from those found in our research where the males presented the highest values, this behavior may be due to the fact that the differences between populations are very difficult to explain, but it is known that the morphometric characteristics may have variability in responses to environmental conditions, consistent with the evolutionary hypothesis where it is stated that divergent habitats drive interspecific phenotypic diversification, which are important for predicting adaptive responses of freshwater fish species to different zones and anthropogenic currents modification. These morphological differences between populations of a species may be related to habitat conditions such as temperature, turbidity, food availability, water depth and flow (31,32,33).

In this sense, González et al (10) and González-Martínez et al (13), when evaluating the morphometric variations between two populations (wild and cultivated) of the species Cichlasomafestae and Dormitatorlatifrons, reported increases of 22.78 g, 0.61 and 2.26 cm for weight, Condition factor and the total length for C. festea; while, for D.latifrons, differences were only reported for weight with increases of 2.71 g. The introduction and crossbreeding of a fish (especially wild ones) lead to a high adaptation to a wide range of geographical locations, which leads to phenotypic variations regarding the pure stock (strains) of the reproducers. Hence, the cause of the variation in morphometric characters can be attributed in part to interspecific variability, which is under the influence of environmental parameters where fish adapts quickly change the necessary morphological characters. Therefore, the differences between both production systems could be explained by the availability of more food for fish in fish farms than in rivers, the latter depending more on climatic conditions (34). That is why, since there were no large fluctuations in these conditions in the different regions sampled, no differences were recorded between the areas.

Ochoa-Ubilla et al (30), when studying the weight-length relationship of economically valuable species (Ichthyoelephashumeralis, Leporinusecuadoriensis, Brycon spp., Rhamdia cinerascens, Andinoacara rivulatus, Hoplias microlepis, Pseudocurimata spp.) captured in Abras de Mantequilla wetland, Ecuador; potential growth equations were obtained for all species, but I. humeralis, A. rivulatus and P. spp., with negative allometric growth, while .. microlepis, L. ecuadoriensis, Brycon sp., and R. cinerascens with isometric growth. The differences between growth could be related to many factors, such as the size of the samples, size ranges, genetic aspects between groups of species and environmental conditions. In addition, the weight-length relationship can behave differently not only between species, but also within populations of the same species, since growth depends on environmental, nutritional, and genetic variations.

The Condition Factor relates to the fish body condition and reproductive status. Aspects that explain the results obtained by Moreno et al (22), where this parameter was higher for maturing females with more than 172 g, followed by spawned ones, those that are maturing with less than 172 g, and males. Similar results for the Condition Factor have been previously described for the painted catfish, Pseudoplatystoma corruscans, with values ​​close to 1.19 for maturing females, 1.15 for spawned females and 1.1 for males in different stages of gonadal maturation. The decrease in the Condition Factor of the females during spawning is because the animals lose weight without decreasing their size (35).

For their part, Moreno et al (22) when evaluating the total length-live weight relationship of Eremophilus mutisii in maturing females and males, potential equations with R. higher than 0.88 (p<0.05) where the allometric coefficient of the total length-live weight relationship was higher for the females (p<0.05). This suggests that the increase in weight as a function of size is greater in females than in males, especially during gonadal maturation, which may be related to the differences that exist in the weight of the gonads, where the gonadosomatic index was superior for females.

The study of blood parameters in native fish (Table 4) is very limited. Serum biochemistry in fish can assess the animal’s response to stress, diseases, and nutritional imbalances. The disorders that can occur from these factors depend on the species, age, physiological phase. The concentration of cortisol, glucose and cholesterol can be affected by hypoxic stress; therefore, these parameters are essential to know the state in which the animal is (18,36).

In serum parameters of Brycon amazonicus and Astronotus ocellatus breeders, Van der Laan (3) found glucose and cholesterol levels of 64.39 mg/dL and 253.4 mg/ L, values within normal levels for these species (14.7-155.3 mg/dL and 78 to 397 mg/dL, respectively) (17), the glucose results reported in this study are higher in the Quevedo area (162 mg/dL) and lower for cholesterol 130 mg/dL. The variations found in these biochemical parameters may be due to inter or intraspecific factors like genetic variation, gonadal maturation, age, eating habit, stress, habitat, and climate. Slightly high glucose levels are closely related to the nutritional status, diet, and temperature to which the fish are subjected, and can cause a decrease in growth, an increase in glycogen in the liver and can eventually lead to death (37).

In T. natans, Hernández-Cuadrado et al (38) studied the ecophysiological effect on blood biochemistry in specimens captured in five areas, La Bahía swamp, Lagunar Complex of Malambo, Atlántico, Colombia; where two parallel studies were established in culture and wild conditions. The results showed the no differences between the different natural habitats and breeding ponds for cholesterol 280.00 and 281.00 mg/dL; glucose in captive fish did not differ (120.60 mg/dL), however, glucose varied in fish sampled in the wild with its highest values of 140.20 mg/dL. The higher glucose levels are due to the high energy requirement in the natural habitat. This expense may be related to the availability of space, possibly because the gluconeogenic process may be more accentuated, a process especially important for the central nervous system and red blood cells that need a continuous supply of glucose. Pollutants like naphthalene have been shown to affect the plasma glucose levels of Oncorhynchusmykiss in early stages of development (39). On the other hand, the lack of correlation found in this study between sex and blood parameters contrasts with the general trend among vertebrates where it is common for males to present slightly higher levels than females (40).

In conclusion, this study showed the effect of gender on morphometric indicators, with the best results for males while blood biochemistry showed variability regarding the sampled areas with the highest results for Quevedo because of fluctuations in natural conditions of the environment and food.

All authors declare that during the preparation and preparation of this work there was no conflict of interest.