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.     

Male-female Parental Roles in Sarotherodon galilaeus (Pisces: Cichlidae)

Sarotherodon galilaeus is a predominantly biparental, sexually monomorphic mouthbrooder. 15 spawnings of pairs in the weight range 150–450 g were observed in aquaria. Only clutches of females larger than 320 g were reared jointly; with those of smaller females, the first fish to pick up eggs brooded alone, while the comparatively few eggs left for the second fish were invariably eaten. The latency after which eggs were picked up increased with the duration of spawning and indirectly with fish size. This increase was larger in males than in females, so large males started to collect eggs later than their mates. In small pairs (female weight < 200 g), by contrast, the male would pick up eggs first and carry them alone. This is the case in a smaller congeneric species, S. melanotheron, indicating that the apportioning of broodcare is based on a unitary, size-dependent mechanism among Sarotherodon. Yet picking-up order was not entirely determined by these equations. Some fish did not show any reaction towards the eggs and occasionally males became care-givers despite expected longer latency, seemingly because of aggressive dominance.     

Mouthbrooding in the black-chinned tilapia, Sarotherodon melanotheron (Pisces: Cichlidae): the presence of eggs reduces androgen and estradiol levels during paternal and maternal parental behavior

The black-chinned tilapia (Sarotherodon melanotheron) is considered a paternal mouthbrooder in which the male churns the eggs in his mouth for 14-18 days after they are fertilized. We previously showed that plasma androgen and estradiol concentrations increased significantly between the beginning and end of mouthbrooding. Here we provide evidence that androgen and estradiol are relatively high in prespawning male tilapia, decrease significantly with the initiation of mouthbrooding, and return to and slightly surpass prespawning levels by the end of mouthbrooding. We then test the hypothesis that the initiation of mouthbrooding causes a decrease in androgen and estradiol. We raised single pairs of tilapia in seawater aquaria and conducted two experiments. In the first, we removed eggs from males on the morning of Day 1 of mouthbrooding, followed changes in plasma androgen and estradiol in the afternoon of Day 1 and on Days 6, 11, and 16, and compared them to levels in control males who kept their eggs. Removing eggs from mouthbrooding males on the morning of Day 1 eliminated the decrease in plasma androgen and estradiol observed in the afternoon of Day 1 of mouthbrooding. This demonstrates that the eggs are necessary for the decrease. We observed that, infrequently, the female of the pair would pick up the eggs to brood them in her mouth. In a second experiment, in the afternoon of Day 1, we sampled both the male and female of pairs in which the female brooded eggs. In female-brooding pairs, the females had significantly lower androgen and estradiol levels than prespawning females. The black-chinned tilapia in captivity exhibits both paternal and maternal parental behavior. In both sexes the initiation of mouthbrooding triggers a decrease in androgen and estradiol concentrations. We conclude that the presence of eggs inhibits the pituitary-gonadal axis in both males and females and hypothesize that a chemical signal from the eggs is delaying the initiation of the next brood.     

Somatic characteristics of an Australian population of Oreochromis mossambicus (Pisces: Cichlidae)

Synopsis The Oreochromis mossambicus population of North Pine Dam, Brisbane, Queensland, Australia was studied over three years, from 1985 to 1988. Basic somatic data were obtained and characteristic values of condition factor, sex ratio, gonosomatic index and the relationships between total and standard lengths, and length and weight, were calculated. Standard length is proportional to total length by the formula SL = –0.321 + 0.799 TL. Weight is related to length by the isometric formula W = aL³. Condition factor values spanned the range 0.0254 to 0.0563, with an average of 0.04078 for males and 0.03877 for females. The sex ratio is 1: 1 until maturity is reached (21 cm SL), at which time the catch rate of the sexes varies due to divergent habitat selection behaviour. Average values of gonosomatic index, considered in relation to maturity classification, are similar to those obtained from other populations, however maximum values are generally much lower, at 0.47 for males and 3.62 for females. These characteristic values are compared, with varying degrees of concordance, with those for populations of this species in other countries.     

Kin cohesiveness and possible inbreeding in the mouthbrooding tilapia Sarotherodon melanotheron (Pisces Cichlidae)

Four microsatellite markers were used to study genetic variation among individuals of the mouthbrooding tilapia Sarotherodon melanotheron (Rüppel 1852) caught in separate but adjacent shoals. A comparison was also made with fish from six other localities. Populations originating from riverine environments appear to be panmictic, while samples from open waters such as lagoons showed highly significant heterozygote deficiencies. For instance, at the 33-allele locus SMEL4, 32 homozygous individuals were observed among the 82 individuals from the same lagoon location instead of only five homozygotes expected if random mating occurred. A further assessment of the genetic similarity of individuals within each shoal, validated by robust permutation techniques requiring no precise knowledge of gene frequencies, showed that related individuals tend to aggregate, and suggested that mating occurs preferentially within small groups of kin. Cichlids are often presented as a group of fish where microallopatric speciation takes place. The possible link between kin aggregation, inbreeding and shoaling behaviour we propose here may have important consequences for our understanding of the mechanisms involved in this fast speciation process.     

Reproductive biology of Sarotherodon mossambicus (Cichlidae) in Plover Cove Reservoir,Hong Kong

Synopsis A 16-month study (August 1972 to November 1973) of Sarotherodon mossambicus in the Plover Cove Reservoir, Hong Kong revealed a sex ratio of 1:1 for small fish (below 19 cm standard length), but above this length males predominated in the population. Monthly sex composition also showed this approximately 1:1 ratio except during the months of August and September, when again males predominated. Males and females reached M₅₀ at an average length of 17.8 cm and 16.2 cm respectively. Maturity and gonosomatic index studies showed that spawning occurred from May to October with peaks in June and August, and there were at least two spawnings each year. The relationship between fecundity and standard length of females collected during both spawnings was computed to be F = 118.49L–1150.91.     

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.     

Stock density and mortality assessment of Sarotherodon mossambicus (Cichlidae) in Plover Cove Reservoir,Hong Kong

Synopsis Two methods were used to estimate stock density and two to estimate mortality of Sarotherodon mossambicus (Peters) in Plover Cove Reservoir. The first method for density estimation (the capturemark-recapture method) involved tagging and pelvic fin clipping. The former technique was eventually abandoned in favour of the latter. Using the capture-mark-recapture method the population was estimated to be approximately 50,000. The number of fish recaptured was low (six recaptures out of 1590 fish marked) and undoubtedly led to underestimation of the density. The second method, using differences between catch per unit of effort values, gave a much more acceptable estimate of density—702,900.Mortality data were obtained by routine collections of dead fish and interpretation of catch curve results. The former method revealed that whereas natural mortalities (that is, fishing mortality excluded) of all other stock and indigenous fish reach a maximum in May and June, Sarotherodon mortalities were at a maximum in February but with a smaller post-spawning summer peak between August and October. It is suggested that temperature is the major factor involved in these natural mortalities, though post-spawning mortality is thought to be responsible for the summer peak. Mortality data obtained by the second method, when compared with results of dead fish collections and gill net surveys, suggested that illegal fishing operations caused the greatest mortality and represented 97.75% of the overall mortality of Sarotherodon.     

The oxygen uptake of Sarotherodon niloticus L. and the oxygen binding properties of its blood and hemolysate (Pisces: Cichlidae)

The oxygen consumption of Sarotherodon niloticus L. was found to decline below a critical oxygen concentration of about 2 mg O2/l. An important influence of CO2 on the oxygen affinity of whole blood was observed at all temperatures between 20 and 35 degrees C for gas mixtures containing 5.6% CO2. Purified hemolysate showed extremely high oxygen affinities (p50 = 1.08 mmHg at pH 8.2 and 20 degrees C). Low cooperativity was observed at all temperatures from 20 to 35 degrees C, and pH values between 6.5 and 8.2. The Bohr effect proved to be important at pH values lower than pH 7.5 (phi = delta log P50/delta pH = -0.58 between pH 6.5 and 7.0 at 35 degrees C). The oxygen affinities show high thermal sensitivity without a marked pH influence (delta H value for overall oxygenation at pH was -71.7 kJ/mol). The obtained results are interpreted as adaptations to diurnal variations in ambient temperature and oxygen availability.     

The early ontogeny of the southern mouthbrooder,Pseudocrenilabrus philander (Pisces,Cichlidae)

Synopsis The early development of the southern mouthbrooder,Pseudocrenilabrus philander, is documented from activation until the early stages of the juvenile period. The duration of the embryonic period is about 14 days at 25°C. Development is direct and there is accelerated exogenous feeding into the embryonic period. The pattern of development and the timing of ontogenetic events and structure formation are a reflection of both internal and external environmental conditions. During mouthbrooding, oxygen uptake is facilitated by embryonic respiratory plexuses and flapping of the pectoral fins. At the time of first release from the buccal cavity, the embryos are in an advanced state of development. The switch-over from the temporary embryonic respiratory system to the adult branchial system has occurred. The yolksac serves as a supplemental source of nutrition as the embryos develop their external food-gathering abilities. The skeletal and sensory systems are sufficiently developed to allow the young to return to the safety of the female's buccal cavity. Pigmentation may provide disruptive colouration. The rate and pattern of development of another mouthbrooding cichlid,Oreochromis mossambicus, is similar to that ofP. philander despite their phylogenetic differences, and may be a consequence of similar life-history styles.     

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.     

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.     

Age composition,growth and body condition of the introduced Sarotherodon mossambicus (Cichlidae) in Plover Cove Reservoir,Hong Kong

Synopsis Age composition, growth and body condition of the Sarotherodon mossambicus (Peters) stock in the Plover Cove Reservoir were investigated. The fish in this reservoir have a relatively short life cycle; the stock consisted of mainly two to three age groups. Influx of recruits in September and October maintained a high proportion of O-age group fish in the stock. This percentage remained high until the following March or April when the I-age group attained dominance. Length-weight analyses indicated that S. mossembicus conform to the allometric formula W = aLⁿ with a and n exhibiting marked seasonal variations. Growth was most rapid during the first 20 months of life and decreased noticeably after 30 months. In general growth was limited to those months when the water temperature was above 20° C. Both body condition and visceral fat content exhibited seasonal variations which were not correlated with each other or with variations in temperature. However, body condition appears to be directly related to feeding intensity. Mean body condition decreased with increasing age and also decreased progressively during this study. This progressive decrease was probably related to the progressive decrease in salinity of the water and also the carrying capacity of the reservoir rather than to the nutrient content of the water. Mean values for the body condition of females were in general higher than for males, suggesting that females are more robust than males.Maximum accumulations of fat occurred in June and July, corresponding to the breeding period. Such accumulations are thought to be a prerequisite before spawning.     

Field studies of the behavioral ecology and agonistic behavior of Cichlasoma meeki (Pisces: Cichlidae)

Synopsis The behavior and ecology of the firemouth cichlid were investigated in southern Mexico. Observations were conducted primarily at Laguna Bacalar, Quintana Roo. The fish bred throughout the year, nesting in small rocky crevices. Territories were established either by wandering pairs or by lone males which subsequently attracted mates. Stationary territories were maintained for two to three weeks by both pair members until the young were free-swimming, after which the parents defended the young as they foraged. Brood care lasted approximately three months. The distances at which fish were attacked and the behavior performed varied with the age of the defended young and the sex of the parent, as well as the species and size of the intruder. The sexes differed in their reproductive and agonistic activities. Predation on young was rapid if the parents were diverted from their defense. Serious injuries to adults were not observed to result from intraspecific contests. Such interactions were very common, but were ritualized with physical contact between animals rare. Color patterning varied with breeding interval, sex and behavior.     

The haemoglobins of the fish Sarotherodon mossambicus (Peters): functional significance and ontogenetic changes

The haemoglobin patterns of adult and young larval stages of the fish species Sarotherodon mossambicus were determined by polyacrylamide–gel electrophoresis. Oxygen affinity determinations of the adult and larval haemolysates and of each haemoglobin component of the adult indicates that the affinity changes with the pH, temperature and osmotic pressure. The possible evolutionary significance of the multiple haemoglobins is discussed. The electrophoretic pattern of adult S. leucostictus , a species closely related to S. mossambicus was also determined and used as a comparative study.     

Temperature and pH effects on the total white muscle LDH of Oreochromis niloticus (Pisces: Cichlidae)

The total lactate dehydrogenase enzyme activity of white muscle from O. niloticus shows positive thermal modulation. There is a tendency towards conservation of binding capacity for substrate at physiologically changing pH conditions. Inhibition by excess pyruvate is influenced by temperature and pH, but this phenomenon is not considered to be important in anaerobic glycolysis.     

Body condition and nutritional ecology of Oreochromis mossambicus (Pisces, Cichlidae) populations of man-made lakes in Sri Lanka

The nutritive quality of ingested material of adult Oreochromis mossambicus wild populations from 12 perennial, man-made lakes were evaluated for four climatic seasons. The seasonal variation in condition of each population, and the overall condition of each population, considered as the theoretical weight of a 20cm individual, was computed from the length-weight regressions, which were curvilinear. The mean overall condition of the O. mossambicus reservoir population was 152.6 g ( s.d. ± 9.5) and ranged between 139.8 and 167.8 g. Distinct patterns in the seasonal changes in condition of an individual population were not apparent. The mean percentage of protein and total organic matter (TOM) and calorific content (kJg⁻¹) of the ingested material were 20.7% ( s.d. ± 3.7; range 9.6–35.2%), 46.0% ( s.d. ± 9.8; range 20.9–73.7%) and 11.6 ( s.d. ± 3.4; range 4.6–20.9) respectively. The amount of each of the above components for any one population varied seasonally in relation to the changes in feeding habit. The protein content of the ingested material of those populations devouring predominantly detritus also showed seasonal variability. The amount of protein (mg) in the digestible total organic matter (DTOM) and the calorific content (Cal) in the ingested material were related to the TOM content as follows: The overall body condition (BC) of O. mossambicus populations was linearly rebated to the digestible protein: energy ratio (PER) thus: The study indicates that a mixed diet was superior in nutritional quality to a single-component diet. especially with respect to detrital material.     

Stunting in Oreochromis mossambicus (Peters) (Pisces, Cichlidae): An evaluation of past and recent data from Sri Lankan reservoir populations

Tilapiine fish are known to become stunted under different environmental conditions. Of the tilapia, Oreochromis mossambicus (Peters), once considered to be the aquatic chicken, is now treated as a nuisance species in some countries because of its tendency to stunt easily. O. mossambicus is the mainstay of the commercial gillnet fishery in existence in the multitude of reservoirs in Sri Lanka for over 35 years. Published and new evidence on O. mossambicus population traits are presented with a view to evaluating whether the populations in Sri Lankan reservoirs are stunted or not. The main lines of evidence considered are the mean size at maturity (Lm), the proportion of individuals below 20 cm total length in the commercial landings, and growth performance of the individual reservoir populations. Statistically valid inter-relationships exist between the mean length at maturity and the proportion of undersized individuals (below 20 cm) in the landings, and the ratio of the reservoir catchment or watershed area to surface area. Evidence on Lm indicate that there is a tendency for O. mossambicus populations to stunt, however, evidence on growth and mean landing size do not indicate stunting.     

Histological study of the development of the embryo and early larva of Oreochromis niloticus (Pisces: Cichlidae)

The developmental stages of Oreochromis niloticus are similar to those described in other mouth-breeding tilapias except that, as in zebrafish, no cavity was found in the blastula. Variation in the rate of development of the embryo and larva of O. niloticus was found within a clutch of eggs as well as between clutches. Hatching glands are described for the first time in tilapias. They are widely distributed within the ectoderm covering the head, body, tail, and surface of the yolk sac near its attachment to the embryo. Timing of larval development is similar to that in other mouthbrooding tilapias, but is slower than that found in substrate-spawning tilapias. A pneumatic duct connects the swimbladder to the digestive tract and swimbladder inflation and initiation of feeding occurs at about the same time. The digestive tract of the larva 8 and 9 days after fertilization is similar to that found in the adult, except that there are no digestive glands. An endocrine pancreatic islet was first seen 76 h after fertilization. A prominent thymus gland is present at 100 h. Hematopoietic tissue develops in the vicinity of the pronephros during early larval development. A spleen develops later, 7 days after fertilization.