Chemical communication, aggression, and conspecific recognition in the fish Nile tilapia

The chemical modulation of agonistic behavior and conspecific recognition were tested in juveniles of the fish Nile tilapia, Oreochromis niloticus (L.). After a 7-day isolation period, the fish were grouped (four individuals per aquarium) for 7 days. Then fish of alpha and beta ranks (previously matched for similar size) were paired in a neutral territory for analysis of their agonistic interaction. Pairs composed of alpha and beta fish were established with either fish from the same group (familiar) or from two different groups (unfamiliar). The pairs were tested in contiguous compartments, either with water exchange between the compartments or in the absence of water exchange. In each condition the fish were separated by a transparent glass partition. Twelve pairs were tested in each experimental condition. Fish behavior was videotaped and the following variables were analyzed: (a) frequency of and time spent in agonistic patterns, (b) latency to start fighting, and (c) duration of swimming. Water exchange between compartments decreased agonistic interactions. This effect, however, was more pronounced in pairs of fish coming from the same group (in this case, subordinate fish spent less time in confrontations than dominant ones). We conclude that chemical communication decreases aggression in this species by (1) inducing an alarm reaction and (2) increasing conspecific recognition (thus stabilizing the dominance hierarchy). (C) 1997 Elsevier B.V.

Optimum zinc supplementation level in Nile tilapia Oreochromis niloticus juveniles diets

The present study was designed to determine the optimum dietary zinc supplementation to Nile tilapia juveniles (13.3 +/- 1.13 g), by using vegetable-based diets supplemented with increasing levels of zinc from commercial-grade zinc sulfate monohydrate, a previously determined zinc source of higher bioavailability. The basal diet was supplemented with 25, 50, 100, 150, 200, 300, or 400 mg/kg Zn. The experiment was conducted in forty 250-l tanks arranged in a recirculating water system. The experimental period was divided in two phases. For the first 10-week experimental phase, fish were fed satiation diets supplemented with increasing levels of zinc. For the second 5-week experimental phase, fish that were fed diets supplemented with 0-300 mg/kg Zn during the first phase were fed the 400 mg/kg Zn-supplemented diet; fish fed the diet supplemented with 400 mg/kg Zn (first phase) were fed the nonzinc-supplemented diet (second phase). Broken-line analysis showed that the optimum dietary zinc supplementation ((ZnSO4H2O)-H-.) to Nile tilapia juveniles, using weight gain and bone zinc saturation as response criteria, was 44.50 and 79.51 mg/kg Zn, respectively. When challenged by a zinc-deficient diet, tilapia mobilized stored bone zinc to preserve its zinc status. By considering that bone zinc saturation is a more accurate response criterion than weight gain, it was concluded that the optimum dietary zinc supplementation ((ZnSO4H2O)-H-.) in vegetable-based diets to Nile tilapia juveniles is 79.51 mg/kg Zn. (C) 2004 Elsevier B.V. All rights reserved.

Physiological responses of Nile tilapia, Oreochromis niloticus, fed vitamin C- and lipid-supplemented diets and submitted to low-temperature stress

Water temperature alterations can determine harmful physiological modifications in fish, which should be prepared to cope with this, and nutrition strategies seem to be essential. This study evaluated the effects of different levels of vitamin C and lipids on physiological responses of Nile tilapia, Oreochromis niloticus, submitted to temperature stress. There were two phases: Phase I - preparing fish to store vitamin C and lipid at appropriate temperature, and Phase II - evaluating the contributions these reserves make to fish physiology under low-temperature stress. The experiment used a 3 x 2 factorial design with three vitamin C levels (300, 600, and 1200 mg/kg diet) and two lipid levels (8.0 and 12.0%), plus absence of nutrient test and a diet of 6.0% lipids and 125.0 mg/kg vitamin C. In Phase I, 192 fish were kept at 26.0 +/- 1.0 C for 112 d, and in Phase II, 48 fish were kept at 18.0 +/- 0.5 C for 32 d and at 15.0 +/- 0.5 C for 11 d. Fish fed C0L0 diet showed lower erythrocytes values in both phases; higher vitamin C supplement determined higher red blood cell (RBC) number and higher hematocrit (Htc) (Phase II); Htc was significantly lower in Phase II; after temperature stress, fish fed C0L0 diet had higher mean corpuscular volume, lower hemoglobin corpuscular concentration, and significantly lower vitamin C concentration in the liver; and higher supplementation determined a higher concentration in the liver (Phases I and II). Higher plasmatic cortisol concentration was seen in fish fed C0L0 diet. In conclusion, our results show that the absence of vitamin C in diets impairs RBC formation and does not enable fish to cope with stress; excess vitamin C is efficient in mitigating stress and 600 mg/kg diet is economic and physiologically sufficient to prepare fish for coping with low-temperature stress. Lipid supplementation does not determine alterations in stress biochemical parameters.

2-DEOXYGLUCOSE-INDUCED FOOD-INTAKE BY NILE TILAPIA, OREOCHROMIS-NILOTICUS (L)

The alimentary and glycemic responses to cytoglycopenia were studied in thirty-one Nile tilapia alevins of indeterminate sex and age, measuring on average 10.67 +/- 0.82 cm. The cytoglycopenia was provoked by ip injection of 60 mg/kg 2-deoxy-D-glucose (2-DG, N = 16). The control group (N = 15) was submitted to ip injection of 0.2 ml saline. Blood samples for glucose determination were obtained before and three hours after drug administration by cardiac puncture. Food was then offered ad libitum. One hour later the animals were sacrificed and their stomachs removed. The difference in wet weight between full and empty stomach was utilized to quantify the food intake. Median food intake was 0.3877 g for the fish treated with 2-DG and 0.107 g for the animals injected with saline. This difference was statistically significant by the Mann-Whitney test (P<0.05). The median values of blood glucose levels before drug injection were 46.19 mg/100 ml in the 2-DG-treated fish and 44.54 mg/100 ml in the control group. Three hours after drug administration, the values were 48.64 mg/100 ml in the experimental group and 56.90 mg/100 ml in the control group. The difference between the values of blood glucose before and after the drug was not significant for either group. We conclude that glucoprivation provokes food intake in fish and that the same glucoprivation was not sufficient to provoke hyperglycemia.

HETEROGENEOUS GROWTH IN THE NILE TILAPIA - SOCIAL STRESS AND CARBOHYDRATE-METABOLISM

Increase in heterogeneous growth as a result of grouping in the Nile tilapia, Oreochromis niloticus (L.), is presumed to be partially promoted by the social stress imposed by the dominant fish on the subordinates. Such stress may decrease the energy available for growth. In this study, the effect of social stress on carbohydrate metabolism was studied in adult, growing males. All animals were deprived of food during the experimentation period and pairing was imposed for either 2 or 4 days. Glycemia was measured before and after pairing, and muscle and liver glycogen contents were determined only after pairing. Subordinate fish showed the highest consumption of carbohydrate reserves. This response was caused by the social stress imposed which corroborates the idea that metabolic differences promoted by social stress may be involved in the rouping effect on heterogeneous growth in the Nile tilapia.

Environmental cadmium exposure and metabolic responses of the Nile tilapia, Oreochromis niloticus

The contamination of water by metal compounds is a worldwide environmental problem. This study was undertaken to evaluate the impact of short-term cadmium exposure on metabolic patterns of the freshwater fish Oreochromis niloticus. The fish were exposed to 320, 640, 1280 and 2560 mug/l sublethal concentrations of Cd++ (CdCl2) in water for 7 days. The specific activities of the enzymes phosphofructo kinase (PFK-E.C.2.7.1.11.), lactate dehydrogenase (LDH-E.C.1.1.1.27.) and creatine kinase (CK-E.C.2.7.3.2.) were decreased in white muscle after cadmium treatments, indicating decreases in the capacity of glycolysis in this tissue. Cadmium exposure induced increased glucose concentration in white muscle of fish. on the other hand, cadmium exposure at sublethal concentrations increased phosphofructo kinase and LDH in red muscle of fish. Cadmium significantly decreased total protein concentrations in liver and white muscle regardless of tissue glycogen levels. The data suggest that cadmium acts as a stressor, leading to metabolic alterations similar to those observed in starvation. (C) 2001 Elsevier B.V. Ltd. All rights reserved.

Localized lymphatic sporotrichosis after fish-induced injury (Tilapia sp.)

Localized lymphatic sporotrichosis generally develops after the fungus Sporothrix schenckii is traumatically introduced into skin or mucosa by contaminated plant material. An 18-year-old male fisherman was injured by spines of the dorsal fin of a fish on the left third finger. The lesion became ulcerated, edematous and suppurative and did not respond to tetracycline and cephalexin. Fifteen days after the accident, a nodular lymphangitic pattern of swelling was observed. Histopathological findings and an intradermal test were suggestive of sporotrichosis and mycological cultures confirmed the diagnosis. The lesions resolved after oral treatment with potassium iodide. Sporotrichosis is a common subcutaneous mycosis in Brazil, and there is a previous report in the literature of this disease being acquired via trauma involving fish spines.

DOES SNATCHING FREQUENCY REALLY INDICATE FOOD INGESTION IN THE NILE TILAPIA

The fitness of the snatching frequency as an indicator of food intake in Nile tilapia finger-lings, Oreochromis niloticus (L), was studied. Five groups of four individuals each were used after a two-day starvation period. The hierarchical rank among individuals in the same group was registered. Food in the form of tiny pellets (ranging from 1.30 to 1.95 mm in diameter) was offered, and the individual snatching frequency was observed during a 20-min period. The animals were then sacrificed for evaluation of stomach contents. It was concluded that snatching frequency is not a good parameter to indicate individual food intake in this species when fed as a group with pellets crushed into tiny particles. This raises a problem for investigations that require evaluation of the cumulative effect of competition on food intake, such as growth or conversion efficiency studies. Furthermore, a very low correlation between snatching frequency and food intake was shown in the third hierarchical rank. It is suggested that the linearity assumed in such hierarchies should be reconsidered.

AGONISTIC PROFILE AND METABOLISM IN ALEVINS OF THE NILE TILAPIA

Metabolic differences derived from social stress usually show data with high variance that may hinder the finding of important differences. Since such high variance may be caused by agonistic variability occurring during social interactions, this work tested whether metabolism is associated with agonistic profile in the cichlid fish Nile tilapia, Oreochromis niloticus (L.). Metabolism was inferred from oxygen consumption, resistance to progressive hypoxia and ventilatory rate. Fifteen pairs of alevins were used for each metabolic and behavioral series. An ethogram based on 8 types of agonistic interactions was employed. Agonistic profiles were determined and associated with the physiological parameters later on. The test of canonical correlation showed significant association between some agonistic profiles and metabolism. Ventral nipping and lateral fight appeared as the two most important in promoting association with metabolism.

Use of ideal protein concept for precision formulation of amino acid levels in fish-meal-free diets for juvenile Nile tilapia (Oreochromis niloticus L.)

This study was undertaken in a closed system with Nile tilapia (Oreochromis niloticus) to examine the effects of total replacement of fish meal (FM) by soybean meal. Nile tilapia fingerlings with an average weight of 5.34+/-0.08 g were hand-fed one of the five isoenergetic (approximate to13.5 MJ digestible energy kg(-1)) and isoproteic (approximate to31% of digestible protein) experimental diets to satiation, six times a day during 85 days in eight replicate fibreglass tanks (six fish per tank). The control diet containing FM was substituted by soybean meal, with and without essential amino acids (lysine, methionine and threonine) or dicalcium phosphate supplementation. The supplemental amino acids were added at levels to simulate the reference amino acid profile of Nile tilapia carcass protein, based on the ideal protein concept. The results showed that soybean meal diet supplemented only with dicalcium phosphate was inferior to the control diet with FM and soybean meal diets supplemented with dicalcium phosphate and essential amino acids. Multiple essential amino acids and dicalcium phosphate incorporation in soybean meal diets was associated with performance, whole-body composition and carcass yield equal to that of the fish fed with the control diet containing FM. These data suggest that a diet with all plant protein source, supplemented with essential amino acids, based on tissue amino acid profile, can totally replace FM in a diet for Nile tilapia, without adverse effects on the growth performance, carcass yield and composition.

SYNAPTONEMAL COMPLEX-ANALYSIS IN SPERMATOCYTES OF TILAPIA, OREOCHROMIS-NILOTICUS (PISCES, CICHLIDAE)

Some adaptations of the synaptonemal complex (SC) whole-mounting technique first used in plants permitted its application to meiotic studies in tilapia, Oreochromis niloticus. Direct observation of the chromosome pairing process and bivalent structure during the meiotic prophase of this fish species by light and electron microscopy permitted the analysis of SCs in autosomes and the possible identification of sex chromosomes. The analysis of SCs in spermatocytes of 0. niloticus revealed that all 22 bivalent chromosomes completely paired, except for the occurrence of a size heteromorphism in the terminal region of the largest bivalent associated with the presence of an incompletely paired segment during the synapsis process, which may be the cytological visualization of an XX/XY sex chromosome system in this species.

Effects of pretreatment with rosemary (Rosmarinus officinalis L.) in the prevention of lipid oxidation in salted tilapia fillets

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effects of environmental colour on growth of Nile tilapia, Oreochromis niloticus (Linnaeus, 1758), maintained individually or in groups

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

A New and Fast Technique to Generate Offspring after Germ Cells Transplantation in Adult Fish: The Nile Tilapia (Oreochromis niloticus) Model

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)