Lunar periodicity in the spawning of yellowtail damselfish,Microspathodon chrysurus

Synopsis The reproductive behavior of yellowtail damselfish,Microspathodon chrysurus, was studied off the Caribbean coast of Panama to determine if there is a lunar spawning cycle. Male damselfish prepare nest sites on dead coral surfaces within their permanent feeding territories. Spawning occurs at sunrise and lasts for approximately one hour. Males defend the eggs until hatching, which occurs before the morning of the sixth day of incubation. Males spawn only once a day, but may spawn many times within each reproductive phase. Reproductive activity is highest in the time periods from full to new moon. The timing of this lunar cycle differs from those reported for other marine fishes. The spawning pattern is not consistent with common explanations for lunar periodicity that are based on the role of tides or moonlight. Some implications of these results for the organization of tropical reef communities are discussed.     

Filial cannibalism in Tilapia mariae

In 152 isolated pairs of Tilapia mariae the parents ate 41% of their broods before these reached the frees-wimming stage. The cannibalized broods were usually eaten at the egg-stage. Most brood-eating was done by the males, as concluded from direct observations and from variation between males (but not between females) in the tendency of eat broods. Cannibalistic behaviour was more common when: 1. the relative weight of female (female weight to male weight) was small (< .4) 2. the relative weight was large (> .7) but not too large (> .85) 3. the female was large (> 70 g) 4. the pair spawned at certain times of the year (outside breeding peaks) 5. the spawn was exceptionally small (less than 100 eggs). In normally sized spawns neither the number of eggs nor the size of the eggs or the spawn could be related to cannibalism. The probability of cannibalism was not altered in the second spawnings of the pairs after an experience of a first unsuccessful spawning. Many of these changes in frequency of cannibalism can be related to the males' expected reproductive success. Thus they possibly reflect an underlying natural adaptive variation which partly has been modified by the aquarium milieu.     

Parental care of Tilapia mariae in the field and in aquaria

Synopsis Parental care of Tilapia mariae was observed in nature (Ethiop River, Nigeria) and in aquaria with or without intruders present. In the field, 25–30% of nests are guarded by one parent, normally the female. It is assumed that most missing males have deserted. Males who participate in brood care exhibit both close brood guarding and brood defence at a lower level than females, and hence seem to invest less than females. Broods were guarded under three distinct types: (1) female at the brood, male in surroundings, (2) parents take turns, or (3) parents stay together at the brood. Each pair used predominantly one type until the young swam freely, thereafter type 3. Females defended most in type 3, but male attack rate did not differ among the types. Type 3 seems related to increased risk of brood predation and type 2 to the female's foraging needs, being more common when she is small and the mates do not differ much in size. The unequal guarding times of type 1 indicate rather a low parental investment by the male (and thus risk of desertion) than specialization in roles on equal investment basis. Parental behaviour exhibited in aquaria differed in many ways from that in nature. The role types were indistinct and there were more signs of motivational conflict between the mates. Isolated pairs avoided joint guarding in the embryo period and while switching, female turns were much longer than male turns, unlike in nature. When intruders were added, males attacked them more than did females.     

Male and Female Parental Roles in the Monogamous Cichlid, Tilapia mariae, Introduced in Florida

We documented male and female parental roles of a monogamous fish, the spotted tilapia, Tilapia mariae, in channelized rivers in southern Florida, where this species dominated the fish fauna within 10 years of their introduction. Clearly differentiated parental roles existed between males and females, with females performing nearly all tending of embryos and most tending of free embryos. After young became free-swimming and left the nest, however, males took over primary tending of the school of young while the female patrolled the perimeter of the school and performed nearly all chases directed at predators. Male and female T. mariae also traded off vigilance and feeding, and showed a high degree of intrapair coordination. Experimental removal of one or both parents had major effects on parental behavior and brood survival and integrity. Solitary females took on a parental role intermediate between that of the male and female of a pair. Untended broods were attacked by predators and scattered into aquatic vegetation, and were not observed to reform. Under dense nesting conditions we observed adoption of broods, group rearing of free-swimming young and the presence of non-breeder satellites sharing and defending a territory with breeders. This highly complex parental care may have allowed T. mariae to invade fish communities dominated by uniparental centrarchids, as well as allowing them to use disturbed habitats such as channelized rivers that are of poor quality for nesting and rearing offspring.     

Developmental pattern of NADPH-diaphorase activity in the peripheral nervous system of the cichlid fish Tilapia mariae

The distribution of NADPH-diaphorase activity was studied in the cichlid fish Tilapia mariae, during the first developmental stages by means of the tetrazolium salt technique. The reaction product was first found, 48 hours after fertilization (stage 10), in the cells of the olfactory placodes and in the superficial neuromasts. A faint positivity was seen in some hair cells of the otic vesicles. The epithelial cells of the most caudal part of the intestinal tract showed a strong labeling. At stage 12 (hatch), the reaction product was in addition detected in scattered enteric neurons surrounding the digestive tract. At stage 13 (4.5 days after spawning), the reaction product was also found in the putative sympathetic trunk, which supplies the gill arches and digestive tract. The epithelial cells of the gastrointestinal canal showed a more strong positive labeling and two large clusters of cells near the pronephritic tubules (the putative adrenomedullar tissue) were also labeled. The present results indicate an early activity of NADPH-diaphorase during the development of the peripheral nervous system of Tilapia and reveal a gradual maturation of NADPH-diaphorase positive structures.     

Lunar synchronization of spawning in cichlid fishes of the tribe Lamprologini in Lake Tanganyika

Lunar synchronization of spawning was investigated for eight substrate brooding cichlid fishes belonging to the tribe Lamprologini. Their spawning activities all peaked during the second quarter of the lunar cycle. Comparison between their breeding styles and the degrees of spawning synchronization suggested that the nocturnal guarding-efficiency of eggs, especially exposed ones, is improved by the maximal amount of moonlight during full moon and, in species whose young leave the breeding sites about 2 weeks after spawning, the survival of dispersing young is enhanced by the darkness of moonless nights.     

Rotifers of Benin River,Nigeria

Plankton hauls were made with 55 m Hydrobios nets at one Jamieson and six Benin River stations at monthly intervals for 12 and 24 months during 1981/82 and 1986–1988, respectively. In all, a 100 km stretch of the Benin River and its tributary, the Jamieson, were covered. Fifty species of Rotifera were recorded. About 80% were cosmopolitan. The turbulent nature of the river is reflected in a diversity of Lecanidae found, although the dominant species were Keratella tropica (Apstein) and Keratella cochlearis (Gosse) (Brachionidae). Spatial investigations revealed the euryhaline nature of Brachionus plicatilis (O. F. Muller), and showed most Benin River rotifers to be freshwater inhabitants.     

Ecology of the Ogun River estuary,Nigeria

The distribution of benthonic communities (particularly Foraminifera) were studied from fourteen samples obtained from the Ogun River estuary and environs. Ten species of benthonic Foraminifera were identified; two of these constitute over 90% of the total foraminiferal population.Two broad biofacies are recognisable, namely the upper estuarine facies of Ammobaculites and the lower estuarine facies comprising arenaceous and calcereous forms with a preponderance of Ammonia beccarii (Linnaeus).Large populations of few species occur in the lower estuary, an area of weakly saline water with marked salinity fluctuations. The upper estuary on the other hand is sparsely populated and contains tests mainly of arenaeous Foraminifera. A few species are distinctive of particular facies but some are distributed throughout the estuary. Substrate is not a causal ecological factor, because sediments are similar in physical attributes throughout the estuary. Salinity and rate of sedimentation are among the more important factors affecting the distribution of all species. The low-energy nature of the environment is established by the abundance of faecal pellets and the fragility of the tests of the arenaceous Foraminifera.     

Limnology and plankton periodicity of Jos Plateau water reservoir,Nigeria, West Africa

Limnological data (Dec. 1980–Jan. 1982) on the plankton and water chemistry of Lamingo Dam, located within the Jos biotite granite area of the Plateau State (Nigeria) are presented. The water-body falls in Beadle's (1981) category I of African lakes (conductivity < 40 µS cm^–1). Alkalinity (% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGabmiEayaara% aaaa!3914!\[\bar x\] = 0.3 meq l^–1), principally composed of bicarbonates, dominated the anions % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaK4waiaajI% eacaqIdbGaaK4tamaaxababaGaeyOeI0caleaacaaIZaaabeaakiaa% b6dacaqIdbGaaKiBaiaaj2cacaqG+aGaaK4uaiaaj+eadaqhaaWcba% GaaKinaaqaaiaajkdacaqITaaaaOGaaKyxaaaa!4657!\[\user1{[HCO}\mathop -\limits_3 {\text{ > }}\user1{Cl - }{\text{ > }}\user1{SO}_\user1{4}^{\user1{2 - }} \user1{]}\]The plankton were characterized by a moderate standing crop of phytoplankton, and zooplankton were, generally, very limited in species and abundance. The order of dominance for the categories of phyto and zooplankton was: [Bacillariophyceae > Chlorophyceae > Dinophyceae] and [Rotifera > Crustacea] respectively. A diel cycle was characterized by nocturnal upward migration of the zooplankton, and the reverse behaviour in the phytoplankton.Interrelations between the biotic assemblages of plankters and various physical and chemical variables are discussed.     

Water quality and plankton periodicity in two contrasting mine lakes in Jos,Nigeria

Water quality and plankton periodicity was studied in two mine lakes near Jos in the younger granite area of Plateau State, Nigeria. The investigation was carried out for 8 months. Transparency, pH and NO₃-N were significantly higher in Lake II while DOM, alkalinity, PO ₄ ^3– -P, BOD and chloride were significantly higher in Lake I. The order of dominance in Lake I was Bacillariophyceae, Cyanophyceae, Chlorophyceae and Dinophyceae while for Lake II; Chlorophyceae, Cyanophyceae, Bacillariophyceae and Dinophyceae. In Lake I the zooplankton in order of dominance were Cladocera, Rotifera, Copepoda, and nauplii and in Lake II Cladocera, Copepoda, Rotifera and nauplii. Although both lakes would seem unproductive based on the PO ₄ ^3– -P and NO ₃ ^– -N levels, Lake I appears more productive than Lake II.     

The rotifers of Warri River, Nigeria

The rotifer assemblage of the dendritic tidal Warri River wasinvestigated at four sampling points from July 1981 to July1982. Forty-one species of Rotifera were identified. Five ofthese — Anuraeopsis racenesi Berzins Keratella cochlearismacracantha Lauterbom, Monostyla lunaris Pawlowsky,M. stenroosiMeissner and Trichocerca similis grandis Hauer — are beingrecorded for the first time in West Africa. The Warri Riverrotifers are 65% cosmopolitan and 20% pantropical although therewas no species limited to African waters only. The dominantrotifers in the Warri River were Keratella tropica and K. cochleariswhich were found in the predominantly freshwater sampling stationat Udu Bridge to Warri and Orugbo Creek where low brackish watersalinities and conductivities are observed from December orJanuary to April each year. The preponderance and longitudinaldistribution of these two well-known cyclomorphic rotifers providesan opportunity to study their salinity tolerance and the effectof salinity and conductivity on their cyclomorphosis by samplingalong the length of the river from Udu Bridge to Forcados wherethe Warri River joins the Atlantic Ocean.     

Lunar rhythms in the deep sea: evidence from the reproductive periodicity of several marine invertebrates

While lunar rhythms are commonly documented in plants and animals living in terrestrial and shallow-water environments, deep-sea organisms have essentially been overlooked in that respect. This report describes evidence of lunar periodicity in the reproduction of 6 deep-sea species belonging to 2 phyla. Occurrences of gamete release in free spawners and larval release in brooders exhibited significant peaks around the new and full moons, respectively. The exact nature of this lunar period (endogenous or exogenous rhythm) and its adaptive significance in the deep sea remain elusive. Current knowledge suggests that proxies of moon phases at depth may include fluxes in particulate matter deposition, cyclic currents, and moonlight for species living in the disphotic zone.     

Salinity and the distribution of Cladocera in Warri River,Nigeria

Hydrobiological investigations of the water quality and plankton of Warri River started in 1981, shortly before the commissioning of the Delta Steel Plant on the banks of the river at Aladja. The 150 km of river gradates from pure freshwater through brackish to marine and so provides a suitable habitat for a study of the limits of migration of any group of zooplankton. The Cladocera of Warri River consists of two bosminids, thirteen chydorids, three daphniids, three macrothricids, one moinid, and two sidids. All except the sididPenilia sp. are well known freshwater forms, which are limited in longitudinal distribution to areas with salinity below 2.5‰. Penilia sp. found in Warri River were restricted to the truely brackish-water areas with salinity values of 7‰ −8‰. In this respect they represent the first reported brackish water Cladocera in Africa. They also differ fromPenilia avirostris Dana found in marine habitats in certain morphological details, and so the Warri RiverPenilia may be a new taxon.     

Spawning periodicity and annual breeding seasons of Tilapia nilotica (L.) in the White Nile

Two annual breeding seasons are indicated for populations of T. nilotica in the White Nile: a major autumnal season (mid-July–September) coinciding with the annual rainfall and a smaller back-up season in February–March. During these seasons reproducing females constituted 80% and 40% of the total population of mature females compared to 10–12% in the intervening summer period. Enhanced gonadal development, fecundity and GSI values characterized the breeding seasons. Gonadal maturation proceeded uninterruptedly even during the summer and repeated fractional spawning is suggested for this species within and beyond the breeding seasons. Most of the spring breeders were either very young or relatively old fish and most medium-sized females bred in the main autumnal season. Older fish were less fecund (by 70–75%) compared to younger fish. In the latter, fecundity increased progressively with body growth (r² = 0.732; p<0.001); the proportionality was lost in medium-sized fish and in older females (0.9–1.5 kg) fecundity correlated negatively with increased body size.     

Water quality assessment of the Siluko River,southern Nigeria

The water quality of the Siluko River, Edo State, Nigeria was investigated from March to August 2015 to determine its suitability for drinking and usage for domestic purposes. Water samples collected from three stations were tested for thirteen physico-chemical parameters using standard analytical procedures. Temperature, phosphate and chloride were significantly different across the three stations. All other parameters, with the exception of turbidity, dissolved oxygen and phosphate, were within the permissible limits recommended by the Nigerian Standard for Drinking Water Quality (NSDWQ) and World Health Organization (WHO). Water Quality Index (WQI) values ranged from 11.24 to 16.15, indicating excellent water quality. While the quality of the water from the Siluko River is suitable for drinking and domestic usage, to prevent future deterioration of the water, it is recommended that the regulating authorities monitor effluents discharged into the river from human activities.     

Demography of spawning grayling (Thymallus arcticus) in the Beaverlodge River,Alberta

Changes in a grayling spawning population are described that occurred in relation to both natural and man-induced events. The spawning population was monitored from 1982 to 1987 with a trap on a fishway on the Beaverlodge River, Alberta. Most of the spawning run in each year was tagged with recaptures noted in subsequent years. Male grayling grew slightly faster than females. Growth rates were variable and appeared to be quite low in years of low water flow. Grayling first spawned at 2 to 6 years of age. The majority of tagged grayling would have returned to spawn a second time after a delay of one to two years were it not for the high adult mortality. It is hypothesized that the variable time to first maturity and the delay in the second spawning is a response to highly variable juvenile recruitment. Annual mortality rates increased with age, suggesting an increased vulnerability of larger fish to angling. The population appears highly sensitive to over-exploitation, because of the high mortality rates and the delayed time to spawning of the adults.Deceased.Deceased.