Biology of the small pelagic fishes in the new Volta Lake in Ghana

Summary A number of small pelagic fish species were found in the new Volta Lake in Ghana. Three, the clupeids Cynothrissa mento and Pellonula afzeliusi, and the schilbeid Physailia pellucida, rapidly became dominant, and these together with another schilbeid Siluranodon auritus and the clupeid-like cyprinid Barilius niloticus are here considered. Pellonula and Physailia eat chiefly invertebrates; the former especially at the surface, the latter in mid-depths or at the bottom. Zooplankton is important to all sizes of Physailia, but only to juveniles of Pellonula. Barilius feeds almost entirely on adventitous forms taken at the surface and Siluranodon on algae and rotifers. Cynothrissa, the largest fish studied, feeds mainly on fish. The food range taken is thus wide, and differences in diet are discussed in terms of the probable future of each species in the new lake as it matures.This paper is taken from a thesis accepted for the M. Sc. Degree of the University of Dublin.     

Feeding habits of the clupeid Limnothrissa miodon (Boulenger), in Lake Kivu

A limnological sampling programme implemented during 1980 in Lake Kivu, Rwanda, confirmed a seasonal increase of the pelagic plankton biomass at the end of the dry season during the windy period of August/September. From plankton samples taken in the littoral and pelagic zones of the Lake it was concluded that a successful introduction of the freshwater clupeid Limnothrissa miodon Boulenger, during 1958–1960, had not obviously influenced the species composition of the Copepoda in the Lake. Examination of stomach contents of different length classes of Limnothrissa proved that the Kivu clupeid is not a strict planktonphagic species. Its diet is adapted to its life cycle and inshore/offshore migration patterns. In pelagic waters of the lake it is an exclusive plankton feeder, while in littoral waters it has more littoral bound feeding habits. Cannibalism was observed among individuals larger than 100 mm, near the margins of the lake. Echosoundings and periodic observations on stomach contents support the hypothesis that Limnothrissa feeds in the late afternoon and digests its food during the night, while a second feeding/digestion cycle starts in the early morning, at sunrise.     

Dry-season spawning in a cyprinid fish of southern India

Synopsis A population of the S. Indian cyprinid fishBarbus melanampyx was sampled monthly through 24 months. Seasonal cycles of the gonado-somatic index (GSI), ovarian stages, male breeding tubercles, spawning behaviour and population structure were assessed. These fish breed strictly seasonally during the main dry period: December/January through April. Comparison with other Barbus species of the same general region led to the conclusion that the patterns of reproductive investment ofB. melanampyx are similar to those of perennial species, and different from those of wet-season spawners. The reasons for this rather unexpected result were found in the more constant conditions prevailing during a dry season as compared to the monsoon. It was argued thatB. melanampyx and the species spawning perennially are in effect small-brood spawners, rather than partial spawners.     

Spawning and subsequent copulating behavior of the elkhorn sculpinAlcichthys alcicornis in an aquarium

The spawning and subsequent copulating behavior of the elkhorn sculpin (Alcichthys alcicornis) were observed in an aquarium. Soon after the female was introduced into the tank, the male approached and initiated courtship behavior by unfolding all fins. Females which carried ovulated eggs eventually accepted the male and spawning progressed. Females which had not ovulated, repeatedly rejected the male’s advances. The onset of spawning in the female was indicated by fluttering of the pectoral fins and successive horizontal undulations of the posterior trunk which served to sweep the spawning site. The laying of several thousand eggs was preceded by the female taking several large inhalations of water through the mouth and a slight raising of the posterior trunk. The male continued various behavior related to courtship while the female approached spawning. After spawning, the female smoothed the egg mass into a thin layer by using the posterior trunk and anal fin. After spawning, and while the female flattened the egg mass, the male copulated repeatedly. No copulation was observed prior to spawning. Semen was observed to be emitted from the tip of the penis and to leak from the female’s genital pore. Eggs were fertilized externally by the emitted sperm in the case of females which had no prior copulating experience in the present breeding season. The entire reproductive behavior of the pair ceased, as the female left the spawning site after flattening the egg mass. The male remained near by, but did not aerate the eggs. During the breeding season, the area around the female’s genital pore and along both sides near the base of the anal fin became slightly distended and soft by the accumulation of a serous fluid. It is presumed that this edematous modification serves to flatten the egg mass for softness without crushing the eggs.     

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.     

Reproduction and development in some species of the weakly electric genus <Emphasis Type="Italic">Campylomormyrus</Emphasis> (Mormyridae,Teleostei)

Reproduction in captivity of four species of the mormyrid genus Campylomormyrus was investigated. Cyclical reproduction was provoked by changing water conductivity (C) alone: decreasing C led to gonadal recrudescence, an increase induced gonad regression. Data on the reproduction and development of three species are presented. All three species are indeterminate fractional spawners. Spawning intervals ranged from 6 to 66 days in C. rhynchophorus, 10–75 days in C. tshokwe, and 18 days in C. compressirostris (calculated values). Fecundities (eggs per fractional spawning) ranged from 70 to 1570 eggs in C. rhynchophorus, 100–1192 in C. tshokwe, and 38–246 in C. compressirostris. Spawnings/ovipositions occurred during the second half of the night; no parental care was observed; no special spawning substrates were necessary. C. compressirostris successfully spawned in breeding groups, C. rhynchophorus as pair. Agonistic behavior in the C. tshokwe pair forced us to divide the breeding tank; therefore, only ovipositions occurred. However, injection of an artificial GnRH hormone allowed us to obtain ripe eggs and sperm and to perform successful artificial reproduction. All three species produce yolky, slightly sticky eggs. Egg diameter ranges from 2.3–3.0 mm. Hatching occurred on day 3, feeding started on day 11. Transition from larval to juvenile stage occurred at around 20 mm total length (TL). At this size C. rhynchophorus developed a higher body than the two other species and differences between the species in the melanin pigmentation of the unpaired fins occurred. Between 32 and 35 mm TL the upper and lower jaws started to elongate.     

Feral pigs as hosts for Amblyomma sculptum (Acari: Ixodidae) populations in the Pantanal,Mato Grosso do Sul,Brazil

The Pantanal in Brazil is the largest floodplain of the world. This ecosystem, rich in wildlife, has a large feral pig population. Such a large host biomass must have a strong influence on the parasite fauna. In this work, we evaluated the role of feral pigs in the maintenance of Amblyomma sculptum (formerly Amblyomma cajennense), the most prevalent tick species in the Pantanal. Tick infestations were evaluated on 243 feral pigs and their environment. The suitability of domestic pigs, representing their feral relatives, to A. sculptum adults and nymphs was assessed experimentally. Tick infestation of feral pigs was strongly associated with that of the environment: 96 and 97 % of the ticks, respectively, were A. sculptum. The infestation prevalence on this host species was close to 90 % in the dry season and 100 % in the wet season and mean infestation intensity was above 30 ticks in both seasons. Suitability of pigs as hosts for A. sculptum was shown by the high proportion of nymphs and female ticks found engorging on captured feral pigs and adequate biological parameters displayed by ticks from experimental infestations of domestic pigs. Other tick species on feral pigs, albeit in much lower numbers, were Amblyomma parvum and Ornithodorus rostratus. Results show that feral pigs feed a high proportion of the A. sculptum adults and nymphs in their territories and should be a target for tick-borne diseases studies. This is particularly relevant to public health because all the main tick species found on feral pigs are aggressive to humans as well.     

Long-term changes in planktonic associations of crustaceans in Lake Constance and adjacent waters and their effects on competitive situations

Changes in crustacean populations, caused by immigration of new species in the course of eutrophication of a lake, result in the establishment of new relationships between the members of the association. Cyclops vicinus is of particular significance, especially in the period of its maximum abundance it is an important predator of other copepods.     

Single‐parentage assignments reveal negative‐assortative mating in an endangered salmonid

Understanding reproductive patterns in endangered species is critical for supporting their recovery efforts. In this study we use a combination of paired‐parent and single‐parent assignments to examine the reproductive patterns in an endangered population of sockeye salmon (Oncorhynchus nerka) that uses Redfish Lake in central Idaho as a spawning and nursery lake. Recovery efforts include the release of maturing adults into the lake for volitional spawning. The lake is also inhabited by a population of resident O. nerka that is genetically indistinguishable, but phenotypically smaller, to the maturing adults released into the lake. The resident population is difficult to sample and the reproductive patterns between the two groups are unknown. We used results of paired‐ and single‐parentage assignments to specifically examine the reproductive patterns of male fish released into the lake under an equal sex ratio and a male‐biased sex ratio. Assignment results of offspring leaving the lake indicated a reproductive shift by males under the two scenarios. Males displayed an assortative mating pattern under an equal sex ratio and spawned almost exclusively with the released females. Under a male‐biased sex ratio most males shifted to a negative‐assortative mating pattern and spawned with smaller females from the resident population. These males were younger and smaller than males that spawned with released females suggesting they were unable to compete with larger males for spawning opportunities with the larger, released females. The results provided insights into the reproductive behavior of this endangered population and has implications for recovery efforts.     

Environmental conditions modulate plasticity in the physiological responses of three plant species of the Neotropical savannah

Plasticity in plants could be changed due to abiotic factors, tending to increase fitness across environments. In the Neotropical savannah, a strong water deficit during the dry season is one of the main factors limiting the plasticity in physiological responses of plants. The present study aims to assess the plasticity in physiological responses and vegetative phenology of three plant species of the Neotropical savannah (Cerrado in Brazil) during the dry and the rainy seasons. The three species, Byrsonima verbascifolia, Roupala montana, and Solanum lycocarpum, occur in Serra do Cipó in the state of Minas Gerais, Brazil. The development and vegetative phenology of individuals of these three species were evaluated over the course of 1 year. In February 2012 (rainy season) and August 2012 (dry season), stomatal conductance (g _s), water potential (Ψ), photosynthetic quantum yield, and concentration of leaf photosynthetic pigments were measured. The relative distance among the physiological parameters of all individuals within each season was measured using the relative distance plasticity index. B. verbascifolia has pronounced senescence in July and lost leaves completely by the early September, while R. montana and S. lycocarpum have green leaves throughout the year. The three studied species had greater control of stomatal opening during the dry season. S. lycocarpum and R. montana had negative water potential values in the dry season and in the middle of the day in both seasons. In the dry season, the three species exhibited a decrease in F _v/F _m, with values between 0.7 and 0.75. The relative distance plasticity index varied from 0 to 1. R. montana demonstrated the greatest plasticity and S. lycocarpum had lower plasticity. Then, a seasonal effect on physiological response was observed in all three model-species, with lower values for leaf water potential and stomatal conductance, and increased photoinhibition, in the dry season. Ecophysiological traits, such as stomatal conductance and leaf water potential, exhibited the greatest plasticity. In addition, there was a seasonal effect on the plasticity in physiological responses of the three plants species of the Neotropical savannah. The results are contradicting the idea that water restriction in the dry season would reduce the plasticity in most species of the Neotropical savannah.     

Threat-sensitive anti-predator defence in precocial wader,the northern lapwing <Emphasis Type="Italic">Vanellus vanellus</Emphasis>

Birds exhibit various forms of anti-predator behaviours to avoid reproductive failure, with mobbing—observation, approach and usually harassment of a predator—being one of the most commonly observed. Here, we investigate patterns of temporal variation in the mobbing response exhibited by a precocial species, the northern lapwing (Vanellus vanellus). We test whether brood age and self-reliance, or the perceived risk posed by various predators, affect mobbing response of lapwings. We quantified aggressive interactions between lapwings and their natural avian predators and used generalized additive models to test how timing and predator species identity are related to the mobbing response of lapwings. Lapwings diversified mobbing response within the breeding season and depending on predator species. Raven Corvus corax, hooded crow Corvus cornix and harriers evoked the strongest response, while common buzzard Buteo buteo, white stork Ciconia ciconia, black-headed gull Chroicocephalus ridibundus and rook Corvus frugilegus were less frequently attacked. Lapwings increased their mobbing response against raven, common buzzard, white stork and rook throughout the breeding season, while defence against hooded crow, harriers and black-headed gull did not exhibit clear temporal patterns. Mobbing behaviour of lapwings apparently constitutes a flexible anti-predator strategy. The anti-predator response depends on predator species, which may suggest that lapwings distinguish between predator types and match mobbing response to the perceived hazard at different stages of the breeding cycle. We conclude that a single species may exhibit various patterns of temporal variation in anti-predator defence, which may correspond with various hypotheses derived from parental investment theory.     

Hatching patterns and larval growth of a triplefin from central Chile inferred by otolith microstructure analysis

The subtidal rocky reefs are home to a diverse range of marine animals, including small cryptic fishes, characterised by a bipartite life cycle, with benthic adults and pelagic larval stage that lasts from several days to several months. Using the otolith microstructure analysis, this study determines the hatching and larval growth patterns of the abundant triplefin Helcogrammoides chilensis (Pisces: Tripterygiidae). Fish larvae were collected during September–October 2010 and between July 2012 and April 2013 in nearshore waters (<500 m) of central Chile. Nearshore time series of ichthyoplankton samples showed that large abundance of this species occurs during early austral spring and autumn seasons. Body lengths ranged from 3.11 to 16.57 mm (1–57 days old). Sagittal microincrement analyses estimate that during the main reproductive season, larval growth rates are slow, varying between 0.145 and 0.156 mm day^?1 at a weekly scale. Back-calculated hatch days and circular statistics indicate a major hatch pulse occurring near full moon of the lunar cycle. These results suggest that reproduction occurs coupled with the upwelling season, which reduces the probability of starvation, and hatching occurs during spring tides (full moon), which increases larval dispersion and population connectivity.     

Seasonal variation in the biochemical composition of Mytilus viridis at Ratnagiri on the West Coast of India

1. The seasonal variation in the water, protein, fat and glycogen contents of the mussel, Mytilus viridis has been studied for the year March, 1974 to March, 1975.
2. The water level increased during the monsoon season and decreased in summer.
3. The level of protein, fat and glycogen showed correlation with the reproductive cycle of the mussel.
4. The protein level was high when the mussels were mature and dropped during the breeding period.
5. During sex change from male to female in May the protein level remained high whereas during sex change from female to male in October and November it was low.
6. The fat level was high in mature mussels and declined on spawning.
7. The glycogen level was at its peak in immature mussels and low in mature.

     

Male-male interactions and their influence on the mating behavior and success in the fountain darter, <Emphasis Type="Italic">Etheostoma fonticola</Emphasis>

Behavioral interactions between individuals of the same sex can affect the outcome of intersexual selection. For this reason, intrasexual selection is oftentimes examined independently from intersexual selection in studies aimed at understanding mating behaviors. However, a more complete understanding of sexual selection effects within a population can only come from exploring both intrasexual and intersexual selection and the potential interactions between the levels of selection. Association preferences in male and female Etheostoma fonticola do not reveal a size preference for same sex or opposite-sex individuals. However, male-male interactions may influence female choice in E. fonticola. We examined whether male E. fonticola that differ in body size exhibit differences in agonistic behaviors and mating success. Larger males do exhibit higher rates of aggressive behaviors and smaller males, in turn, exhibit more defensive behaviors. However, differences between larger and smaller males in male-male interactions did not translate into differences in spawning success. These results suggest that male size influences dominance relationships in E. fonticola but not mating success. There were also no differences between large and small males in mating attempts, which could be an outcome of the year-round breeding season found in this species, females laying eggs singly, or males fertilizing eggs individually.     

Movements of lumpsucker females in a northern Norwegian fjord during the spawning season

The lumpsucker Cyclopterus lumpus is distributed throughout the North Atlantic Ocean and migrates considerable distances between offshore feeding areas and shallow inshore spawning grounds. The number of the lumpsucker has declined since the mid 1980s, probably as a result of overexploitation. The lumpsucker is the preferred host of the sea louse Caligus elongates, which is a problem for marine aquaculture. However, little is known about the biology of the lumpsucker. The aims of the study were to 1) examine the movements of female lumpsucker during the spawning migration, and 2) assess the potential for lumpsucker to act as a vector for transmission of parasites and diseases between aquaculture farms and wild fish. Twenty female lumpsuckers tagged with acoustic transmitters were released during the spawning season in the inner part of Øksfjord, northern Norway and their distribution was recorded by 22 automatic acoustic receivers. The average time until departure from the fjord was 3 days, and within 1 week all fish had left the fjord. Timing of departure from the fjord was unrelated with either tidal current patterns or the time of the day. A high proportion of the fish (75%) were recorded within 200 m of fish farms, but they did not stay for extended periods at these farms. Our results suggest that mature female lumpsucker exhibit a movement pattern characterized by rapid fjord-scale migrations during the spawning season, and that they are not attracted to salmon farms in the same way as a range of other fish species.     

Centric diatoms from Lake Frolikha (Transbaikal area) and peculiarities of distribution of some taxa in Asia

The species composition of centric diatoms from Lake Frolikha (Transbaikal area) has been studied. The lake is located on the eastern shore of Lake Baikal and connected with it by a river. Twenty-three species of Centrophyceae from 7 genera (Aulacoseira, Cyclostephanos, Cyclotella, Discostella, Handmania, Pliocaenicus, and Stephanodiscus) have been found. The most represented genus is Aulacoseira (11 species). Fifteen species and 4 genera are new for the lake record. All revealed species are known in other lakes of the Baikal region; however Baikal endemics are absent in Lake Frolikha. The flora of centric diatoms in Lake Frolikha can be divided into two groups. The first group includes taxa common in Lake Baikal, and the second group includes taxa not typical for Lake Baikal. The level of differences between flora in Lake Baikal and Lake Frolikha is high (43%) despite the close location and connection to the river. An analysis of distribution of interesting species in Asia is presented.     

Phytoplankton community structure and environment in the Kenyan waters of Lake Victoria

• 1 Phytoplankton species composition, numerical abundance, spatial distribution and total biomass measured as chlorophyll a concentration were studied in relation to environmental factors in September 1994 (dry season) and March 1995 (rainy season), respectively, in the Kenyan waters of Lake Victoria; 103 species were recorded.
• 2 Blue‐green algae (Cyanophyceae) were most diverse, followed by diatoms (Bacillariophyceae), green algae (Chlorophyceae) and dinoflagellates (Dinophyceae).
• 3 Twinspan separated the phytoplankton communities in the Nyanza Gulf and those in the open lake during both seasons. During the dry season, the Nyanza Gulf was strongly dominated by blue‐greens, while diatoms dominated in the open lake. During the rainy season, blue‐greens remained dominant in the Nyanza Gulf although the number of species found was lower than during the dry season; in the open lake, blue‐greens replaced diatoms as the dominant group and there were more species than in the dry season.
• 4 Canonical correspondence analysis indicated that the phytoplankton species distribution was significantly correlated with turbidity during the dry season and with SiO₂ during the rainy season. Chlorophyll a concentrations ranging from 2.0 to 71.5 mg m^‐3 in the dry season and 2.0–17.2 mg m^‐3 in the rainy season confirm earlier reports of increasing phytoplankton biomass in Lake Victoria since the 1960s.

     

Interannual variation in rainfall,drought stress and seedling mortality may mediate monodominance in tropical flooded forests

Flood tolerance is commonly regarded as the main factor explaining low diversity and monodominance in tropical swamps. In this study we examined seedling mortality in relation to seasonality, i.e., flooding versus drought, of the dominant tree species (Prioria copaifera), and three associated species (Pterocarpus officinalis, Carapa guianensis and Pentaclethra macroloba), in seasonally flooded forests (SFF) in Darien, Panama. Seedling mortality differed among species, years and seasons. Prioria seedlings experienced the lowest overall mortality, and after 3 years many more Prioria seedlings remained alive than those of any of the associated species. In general, within species, larger seedlings had greater survival. Seed size, which can vary by close to 2 orders of magnitude in Prioria, had a confounding effect with that of topography. Large-seeded Prioria seedlings experienced 1.5 times greater mortality than small-seeded seedlings, as large-seeded Prioria seedlings were more likely to be located in depressions. This finding suggests that seed size, plant size and topography are important in understanding SFF regeneration. For all species, seedling mortality was consistently greater during the dry season than during flooding. For Prioria, dry season seedling mortality was correlated with drought stress, that is, high mortality during the long El Niño dry season of 1998 and the normal dry season of 2000, but very low dry season mortality during the mild dry season of 1999. Prioria’s ability to dominate in seasonally flooded forest of Central America is partly explained by its low drought-related mortality in comparison to associated species.     

Seasonal and interannual variation of ichthyoplankton off the coast of the Moroccan Sahara

Changes in the qualitative and quantitative composition of ichthyoplankton off the coast of the Moroccan Sahara (21–28° N) in different seasons of 1994–2007 are analyzed. In this region, the pelagic eggs and larvae of over 100 fish species belonging to 62 families have been recorded. In cold periods, off the coast of the Moroccan Sahara there is peak in the spawning of fish of the subtropical fauna. The majority of them are European pilchard Sardina pilchardus, common scad Trachurus trachurus, and Atlantic mackerel Scomber japonicus. In warm periods there is intensive spawning of fish of the tropical fauna. Among them, dominants are round sardinella Sardinella aurita, West-African scad Trachurus trecae, and Atlantic bonito Sarda sarda. The spawning biomass of principal commercial fish is calculated by the quantity of eggs laid by females. The environmental factors are indicated that influence the fluctuation of abundance and distribution of ichthyoplankton in the region under consideration.