Naphthalene-induced changes in carbohydrate metabolism in Sarotherodon mossambicus Peters (Pisces: Cichlidae)

Sarotherodon mossambicus Peters was exposed to naphthalene concentrations ranging from 7.9 to 0.92 mg/l for periods ranging from 4 days to 10 weeks and changes in glycogen, glucose, pyruvic acid and lactic acid contents of liver and muscle were studied. While glucose levels remained unaffected, major effects could be seen in the other constituents following both lethal and sublethal naphthalene treatment. Whereas glycogen and pyruvic acid levels showed considerable reduction, lactic acid levels increased markedly. These changes are indicative of a metabolic stress leading to a shift to anaerobic metabolism. The effects do not appear to be related to the feeding and growth rates of the naphthalene-intoxicated fish.     

Uptake, metabolism and excretion of the molluscicide N-tritylmorpholine by the tropical food fish Sarotherodon mossambicus (Peters)

Uptake, metabolism and excretion of radio-labelled N-tritylmorpholine (Frescon) were studied in the tropical food fish Sarotherodon mossambicus (Peters). After 55 h exposure to sub-lethal solutions, concentration factors in whole fish were as high as 1300 (up to 40 mg/kg), at least 80 % of the absorbed activity being unchanged Frescon. Approximately 40 % of this activity was found in bone, 16% in muscle, 16% in gut and 10% in gill. The bile was found to be a route of Frescon excretion, and recovering fish excreted 50% of the absorbed activity in 55 h. The applicability of these results to the field situation is discussed.     

Morphology of the brain of Sarotherodon mossambicus (Peters) and correlation with its habits

The correlation between the brain of an exotic fish, Sarotherodon mossambicus, and its habits was studied. The poorly developed olfactory lobes are indicative of poor olfactory sense, while the large optic lobes and stout, thick optic nerves correlate with this fish's excellent sense of vision. Similarly, its tactile and gustatory sense are determined by the extent of development of the facial and vagal lobes.     

The effect of temperature and mass on routine metabolism in Sarotherodon (Tilapia)mossambicus (Peters)

A reappraisal of oxygen uptake by Sarotherodon mossambicus was undertaken using a continuous flow respirometer. Measurements were obtained over the temperature range 16°C–37°C for fish weighing between 10 g and 150 g. Oxygen uptake was converted to energy equivalents ( Q _ox) using the value 13.68 J mg O₂^–1and the routine metabolic energy expenditure can be described by the equation E =0.0086 t ^{2 0783} M ^{0 652} where E is the energy requirement for routine metabolism expressed in J h^-1, t the temperature in °C and M the mass in g.     

Sub-lethal effects of the organophosphate blackfly larvicide, Abate (temephos) on Sarotherodon mossambicus (Peters)

Sarotherodon mossambicus was exposed for up to 10 weeks to concentrations of Abate larvicide in excess of those produced during blackfly control in African rivers. Despite this treatment, several indicators of sub-lethal poisoning, e.g. growth, plasma glucose, acetyl-cholinesterase activity remained almost unchanged. A possible explanation for the low toxicity of Abate is given.     

Effect of dietary quality on the gastric evacuation and intestinal passage in Sarotherodon mossambicus (Peters) fry

The gastric evacuation time (GET) and the passage of food through the intestines was investigated in Sarotherodon mossambicus (Peters) fry of two size groups, viz. 0·2–1·0g and 1·0–3·0g, in response to five diets. In the experiments voluntary feeding was adopted and markers were not used. The passage of food through the stomach was described by the exponential model.
The GET increased with body weight for any particular diet, with one exception. The GET ranged from 290 min to 1104 min in fry of 1·0–3·0 g on Diet 2. There was evidence to indicate that the GET was negatively correlated to the specific gravity of the diet.
The passage of food through the intestines showed a consistent trend from diet to diet; e.g. the algal diet being moved into the intestine in 'finite' quanta as opposed to the others. The importance of these observations and the implications of the dependence of the GET on the specific gravity of the diet in the use of markers in digestibility studies are discussed.     

Toluene toxicity: Effects of sublethal levels on enzyme activities in seawater adapted tilapia(Sarotherodon mossambicus Peters)

The effects of exposing seawater adapted cichlid fish, tilapia(Sarotherodon mossambicus Peters) to sublethal concentrations of toluene on the activities of lactate dehydrogenase, succinate dehydrogenase and acetylcholinesterase were studied. The activity of lactate dehydrogenase increased while those of succinate dehydrogenase and acetylcholinesterase were inhibited in most tissues of the exposed fish. The alterations in the dehydrogenases suggested that some changes in carbohydrate metabolism may have occurred. Acetylcholinesterase inhibition in brain and other tissues indicated impairment of nervous function in toluene-intoxicated tilapia.     

In vitro study on the interactive effects of heavy metals on catalase activity of Sarotherodon mossambicus (Peters)

The in vitro effects of individual heavy metal ions as well as their combinations on catalase activity were investigated. Copper was found to be the strongest inhibitor of catalase activity followed by mercury, iron, chromium and cadmium. Copper toxicity on catalase activity was reduced in the presence of all the other metal ions. However, the addition of cadmium, chromium, iron, manganese, lead to mercury and cadmium, iron, manganese, nickel, lead, zinc to chromium increased their inhibitory effects on catalase activity.     

Diurnal changes in the territorial behaviour of the tilapia Oreochromis mossambicus (Peters)

The numbers of black, territorial, male tilapia in large tanks undergoes a clear diurnal cyclicity, with peak numbers seen in the afternoon. It is suggested that this cyclicity is functionally related to an observed spawning cyclicity.     

Switches between zoophagy, phytophagy and detritivory of Sarotherodon mossambicus (Peters) populations in twelve man-made Sri Lankan lakes

The diet of 1200 adult Sarotherodon mossambicus [16–37 cm total length ( t.l .)] in 12 man-made Sri Lankan lakes, belonging to five different irrigational systems were studied over four climatic seasons using volumetric analysis. Food differed between seasons and reservoirs but overall, the diet consisted of 2, 2, 6 and 15 genera of diatoms, blue-green algae, green algae and animal material respectively. However, none of the S. mossambicus populations maintained either a detritivorous, phytoplanktivorous or a zooplanktivorous habit through the year. Detritivory was most common during the rainy season while phytoplanktivory predominated in the dry season. Blue-green algae were not an important constituent of the diet. Out of the 12 reservoir populations, five were predominantly detritivorous, six phytoplanktivorous and one zooplanktivorous. Detritus was completely absent in the ingested material in certain populations when they devoured animal or plant material, indicating the ability of S. mossambicus to switch from deposit to suspension feeding. The mean relative intestinal length (m.r.i.l.) of S. mossambicus ranged between 5–1 and 15–2. The m.r.i.l. decreased significantly with increasing body length: m.r.i.l. = 14–1 –0.018 T.L. ( r =–0.89; P <0.001).     

Immunostimulatory effect of azadirachtin in Oreochromis mossambicus (Peters)

The effect of azadirachtin, a triterpenoid derived from Azadirachta indica on the immune response was studied in the freshwater teleost, O. mossambicus. Bovine serum albumin (BSA) and sheep erythrocytes (SRBC) were used as antigens to evoke immune response. The immune responses in fish were measured by quantifying antibodies produced and counting the peripheral blood leucocytes in control and experimental fish. In general, azadirachtin significantly enhanced the antibody response and leucocyte count in a dose dependent manner. An inverse relationship was observed between the dose of azadirachtin and the degree of immunostimulation. Timing of azadirachtin administration in relation to immunization revealed that the maximum enhancement of antibody response was observed when the stimulant was given two days prior to immunization. The observed immunostimulatory property of azadirachtin has an implication in the maintenance of finfish health in freshwater intensive aquaculture practices.     

The effects of early and late androgen treatments on the behavior of Sarotherodon mossambicus (Pisces: Cichlidae)

Groups of Sarotherodon mossambicus were treated with androgen by immersion or oral treatment at various stages of development. Fish were allowed to mature and the effects of treatment on gonadal and behavioral differentiation were examined. The effects of treatment on gonadal differentiation were assessed by determining the sex ratio for each group. Three treatments resulted in sex ratios significantly different from the 1:1 sex ratio obtained in untreated fish. Behavioral differences were detected between groups of males in three measures of territorial defense and aggression, and differences were detected between groups of females in two measures of male-female courtship interaction. A second experiment determined that early-treated females were more sensitive to a second androgen treatment later in life than females not exposed to androgen during development. A number of sex-reversed genetic females functioning as males were detected in two treatment groups with predominantly male sex ratios. There were no differences in the behavior of sex-reversed and non-sex-reversed male fish from the same treatment group. This study establishes that hormone treatments administered during development influence behavioral differentiation in a teleost.     

Changes in developmental profiles of brain gangliosides during ontogeny of a teleost fish (Sarotherodon mossambicus,Cichlidae)

Summary Ontogenetic changes of brain ganglioside concentration and composition have been followed in the teleost fishSarotherodon mossambicus Cichlidae) from the 1st day post hatching to the adult stage, in order to correlate these with findings in higher vertebrates. During the developmental period from hatching to the transition to free swimming, which comes along with maximum rate of synaptogenesis, a sharp rise in the brain ganglioside content occurs, which is mainly due to the trisialoganglioside GT1b. In the following phase of myelination (characterized in birds and mammals by an increase in GM1, GM1 and GM4) accretion of the novel and so far unidetified fraction (GM2) occurs, which is highly enriched in the brain stem. The results obtained are discussed with respect to gangliosides as useful biochemical markers for brain development and maturation in all vertebrates.     

The distribution of the freshwater cichlid Sarotherodon mossambicus in estuarine systems

Synopsis The distribution of Sarotherodon mossambicus in south east African estuaries is reviewed. It occurs commonly in closed estuaries and coastal lakes but is absent from open tidal estuaries. When a closed estuary opens to the sea the species usually retreats to the upper reaches. It is euryhaline and eurythermal and can feed on a wide variety of foods but experiments indicate that S. mossambicus avoids areas where current speeds exceed 370 m h^–1. It is concluded that the distribution of S. mossambicus in estuarine systems is governed by an interplay of the following factors: salinity stability, water currents, suitable breeding sites, presence of marginal vegetation, marine competitors and marine piscivorous fish.     

The effect of water acidification on prolactin cells and pars intermedia PAS-positive cells in the teleost fish Oreochromis (formerly Sarotherodon) mossambicus and Carassius auratus

Summary Although exposure to acid water (pH 3.5) induces severe and prolonged reduction in plasma osmolarity and total plasma calcium concentration in tilapia (Oreochromis mossambicus) and goldfish (Carassius auratus), the responses of the hypophyseal cells are clearly different. In tilapia, the size of the rostral pars distalis of the pituitary gland is enlarged as a result of the increase in size and number of prolactin cells. The pars intermedia PAS-positive (PIPAS) cells are not noticeably changed. Conversely, in goldfish, prolactin cells are unaffected, whereas the number of enlarged PIPAS cells increases markedly. Stimulation of prolactin secretion may be responsible for the partial restoration of plasma osmolarity and calcium levels observed in tilapia after two weeks exposure to acid water. Prolactin cells apparently play a role in the adaptation to acid stress by counteracting osmoregulatory disturbances. Goldfish show no restoration of plasma osmolarity during the course of the experiment. Plasma calcium levels tend to increase. Although prolactin may have an osmoregulatory function in goldfish under steady state conditions, goldfish prolactin cells do not seem to participate in the physiological adaptation to environmental changes that disturb water and ion homeostasis. The function of PIPAS cells in tilapia remains unclear and is apparently unconnected with ion regulation. The observations on these cells in goldfish are consistent with the hypercalcemic activity suggested for them.     

Lysosomal stability in Oreochromis mossambicus (Peters) on exposure to surfactants

The three commonly used surfactants viz. anionic sodium dodecyl sulfate (SDS), cationic cetyl tri methyl ammonium bromide (CTAB) and non-ionic triton X-100 were toxic even at sub lethal levels (1 ppm for 30 days) to 0. mossambicus. Lysosomal stability index (LSI) was lowest in triton-exposed animals in vitro. In vivo, CTAB was the most toxic. SDS, the anionic surfactant was the least toxic. The possible role of surfactant structure, critical micellar concentration (CMC) and metabolism in influencing the toxicity is discussed and mechanism of action via membrane lipid peroxidation is suggested.     

Food consumption of Sarotherodon mossambicus (Trewaves) exposed to sublethal concentration of diammonium phosphate

S. mossambicus was exposed to toxic and sublethal concentrations of the fertilizer diammonium phosphate (0.2 to 1.0 g l^–1). Mortality, food utilization and growth were studied. At a concentration of 0.6 g l^–1 DAP, 100% mortality was observed within 96 h; no mortality occurred at 0.5 g l^–1; LC50 was 0.55 g l^–1. Rearing the fish in increasing sublethal concentrations of DAP, it was found that the feeding rate decreased from 25.4 mg g^–1 fish^–1 d^–1 (fish reared in DAP-free water) to 10.1 mg g^–1 d^–1 at the highest sublethal concentration (0.5 g l^–1). Growth rate was drastically reduced. At high sublethal concentrations of DAP, the fish lost reserve energy, in addition to the energy obtained from food intake for survival, as a result of increased swimming activity and opercular beats.     

Observations on the nesting habits of Oreochromis mossambicus (Peters) (Pisces: Cichlidae) in Sri Lankan reservoirs

The nest-building characteristics of Oreochromis mossambicus (Peters) were studied in five manmade lakes (reservoirs) Sri Lanka. The nests were always found in clusters (arenas) and were generally located in or near coves and/or bays in shallow water. The density of nests in an arena varied between arenas in a reservoir and between reservoirs. The overall mean density of nests ranged between 0.47 and 6.31 m ² in the five reservoirs. The nests ranged from 11 to 110 cm in diameter, two size groups of nests being recognizable: small, with diameter 10–50 cm, and large with diameter >50 cm. At any nesting site only one size group of nests was found.
Nest diameter ( ND ) was curvilinearly related to mean nest density ( D ) and linearly to mean distance between nests ( Dis ), the respective statistical relationships being
The diameter of nests was also related to nest depth ( Dep ) as
There was no apparent relationship between nesting characteristics and morphometric characters of the reservoirs.     

Differential habitat utilization by sexes of Sarotherodon mossambicus in Lake Valencia, Venezuela: significance for fitness

Adult male and female Sarotherodon mossambicus in Lake Valencia, Venezuala select different littoral habitats. Males prefer areas with soft bottoms and high turbidity, while females favour areas with hard bottoms and low turbidity. Soft bottoms provide suitable sediment for male breeding site construction and high turbidity helps protect territorial males from visionally orientated predators, but the food available in this habitat is of poor quality and males feed relatively little. The hard bottom littoral provides food of superior quality and females feed in these areas. Condition factors are highest for subadult males, intermediate for adult females and lowest for adult males. Differential habitat utilization by sexes of S. mossambicus in Lake Valencia appears to contribute to individual fitness by providing males and females with specific requirements for reproduction.     

Responses of the PAS-positive pars intermedia cells in the cichlid fish Sarotherodon mossambicus to ambient calcium and background adaptation

Summary The function of the PAS-positive pars intermedia cells in fish has been connected with control of background adaptation and of plasma calcium levels. Since background reflectivity and illumination influence calcium metabolism in S. mossambicus, we have tested the hypothesis that the effects of background reflectivity on the PAS-positive cells are mediated by changes in plasma calcium. However, total plasma calcium does not correlate with the activity of the PAS-positive cells as estimated by morphometrical criteria. Transfer of S. mossambicus to a white background leads to a drop in plasma calcium, and a marked reduction of the activity of the PAS-positive cells. Adaptation to low-calcium freshwater, on a neutral background, has the same effect on plasma calcium but has no effect on the PAS-positive cells. The characteristic structural features of highly active PAS-positive cells in fish from a black background are not due to the slight hypocalcemia that occurs in these fish, since addition of calcium to the water in concentrations that fully prevent the drop in plasma calcium does not suppress the PAS-positive cells. These findings make it very unlikely that these cells produce a hypercalcemie factor in S. mossambicus.