Reproductive Biology of the Halfmoon Grouper, Epinephelus rivulatus, at Ningaloo Reef, Western Australia

The reproductive biology and sexual pattern of Epinephelus rivulatus were examined within the waters of Ningaloo Reef, Western Australia. Population structure and gonad morphology show that E. rivulatus is a protogynous hermaphrodite. Mature females ranged in size from 144 to 350mm fork length (FL), with 50% sexually mature at 194mm FL. Males were larger than females and ranged in size from 221 to 381mm FL. There were also intrasexual differences in body size and the median size at which sex-change occurred within each site. Sex ratios were consistent between sites with approximately one male to 5.5 mature females. Most female E. rivulatus (>50%) were reproductively active from July to December when water temperatures were relatively cool and daylight hours were increasing. During this time reproduction occurred periodically, and a female was capable of spawning at least twice over two or three consecutive days.     

Population changes in sympatric Great and Long-tailed Cormorants (Phalacrocorax carbo and P. africanus): the effects of niche overlap or environmental change?

Between January 1993 and January 1995, the number of Great Cormorants (Phalacrocorax carbo) using Lake Naivasha, Kenya (00° 45 S, 36° 20 E) for foraging and resting increased 56%, while the number of sympatric Long-tailed Cormorants (Phalacrocorax africanus) decreased 64%. In 1995 and 1996, we documented habitat changes and conducted monthly population and resource-use surveys of the two species in an attempt to discover the most likely reasons for these changes. The increase in Great Cormorants was probably the result of immigration from nearby Lake Nakuru due to extreme water level reductions there. Lake Naivasha also experienced falling water levels and transparency during this period, but these changes were not as severe and are not considered likely reasons for the decline in Long-tailed Cormorant numbers. Despite some probable dietary overlap, the two species were well separated in terms of foraging locations, foraging methods, resting habitats and breeding timing. The decline in Long-tailed Cormorant numbers may be connected with increased disturbance by fishermen along the lake littoral, this species' primary feeding location.     

Size at sexual maturity,egg number and reproductive output of the snapping shrimp Alpheus euphrosyne euphrosyne De Man, 1897

Abstract

Aspects of the reproductive biology of snapping shrimp Alpheus euphrosyne euphrosyne inhabiting a tropical estuary were studied between August 2007 and July 2008 by examining 1309 females of 8.5–21.5 mm carapace length. Although the occurrence of ovigerous females was noted from October, the main breeding season extended from January to March. Size at 50% sexual maturity was estimated as 10.6±1.40 mm CL. Number of eggs per brood ranged from 141 to 1553 in females of 11.2 to 19.2 mm CL and mean absolute fecundity was estimated as 480±272 eggs. Regressions of log egg number on log total length, log carapace length and log weight revealed isometric relationships (p <0.01). Results of ANOVA revealed significant variation between mean short and long axes of eggs among five embryo developmental stages (P <0.05). The estimated egg batch 33 volume ranged from 4.99 to 32.09 mm³ with a mean of 12.44 mm³. Estimates of reproductive output from 41 females ranged between 8.21 to 31.25% with a mean value of 18.55±5.81.     

A Study of a population of Micronecta scutellaris Stal (Hemiptera : Corixidae) in Lake Naivasha,Kenya

Micronecta scutellaris is one of the most abundant macro-invertebrates found in Lake Naivasha, Kenya and forms an important component of the diet of juvenile large mouthed bass.Its distribution in the lake and breeding biology are described and considered in relation to the lake's food chains.     

Reproductive biology of brown trout, Salmo trutta macrostigma Dumeril 1858, in a tributary of the Ceyhan River which flows into the eastern Mediterranean Sea

The study describes some key elements of the reproductive biology, including spawning season, age at sexual maturity, fecundity and egg diameter of the native brown trout, Salmo trutta macrostigma, in a tributary of the Ceyhan River. A total of 197 brown trout (118 females and 79 males) were captured in 2000–2001 by electric fishing. In observations on monthly changes, the gonadosomatic index (GSI) and the monthly frequency distribution of egg diameter confirmed that spawning lasted from November to January. Some 27.7% of the females and 62.5% of the males attained sexual maturity in their second year. The smallest fork length (FL) of brown trout attaining sexual maturity was 17.4 cm for males and 17.8 cm for females. Mean fecundity in age groups II, III, IV and V were 360, 452, 693 and 1283 eggs per female, respectively. One 9‐year‐old female had a unique 3232 egg count. The mean fecundity of the sampled population was 554 eggs per fish, positively correlated with the FL (mm) (R = 0.8227 ) and body weight (R = 0.8130). The diameter of mature eggs in the spawning season ranged from 3.250 to 5.930 mm, with a 4.146 mm average. Mean egg diameter in age groups II, III, IV and V in the spawning season were 0.813, 3.799, 4.663 and 5.243 mm, respectively. Fecundity, egg weight and diameter were statistically different in all age groups.     

Contribution to knowledge of the biology of Alestes macrophthalmus gunther (Pisces: Characidae)

Summary Contributions to the biology of Alestes macrophthalmus in Central Africa are reviewed and methods of data collection for the purposes of the present work are given. The structure and sexual composition of the L. Bangweulu A. macrophthalmus population, based on the data collected, are discussed. It was found that fish had four stages in the life cycle: a juvenile inshore stage, up to 50 to 70 mm; a juvenile offshore stage, 70–110 mm; an adult, predominantly male (70%), inshore population with the mode at 140 mm; and an adult, predominantly female (70–80%) offshore stage with the population mode at 200 mm. The population died out by 340 mm. The occurrence method was used in the analyses of stomach contents. Thirty two different food constituents were found, but seven of these constituted 94.6% of all food taken. Feeding behaviour was found to change as fish grew, with minnows dominating other constituents after a length of 160 mm had been reached. The question of size of fish prey in relation to shape is discussed. Seasonal changes in diet appeared to be dependent on availability of food. The Bangweulu Alestes were found not to be anadromous, breeding taking place primarily along the sandy wave washed western shoreline. Eggs were demersal. Breeding occurred throughout the year, but was concentrated in September and December. Male fish were more precocious than females and breeding appeared to be dependent on female activity. The linear regression of eggs on fork lengths for lacustine fish plotted as egg production per unit length show that as fish increase in length the proportionate number of eggs produced also increases, but at an ever decreasing rate. Lake fish appear to be more fecund than swamp fish. Mean egg production of 39 fish subjected to egg counts was approximately 10,000. Individual fish bred at least twice each year. A growth curve is postulated on evidence which is not entirely satisfactory. It is suggested that fish take a year to reach 80 mm, reach 120 mm by the end of their second year, 190 mm by the end of their third, 250 mm by their fifth, during which year they die. The possible reasons for the migrations of age groups, and the ecological effects of the species in Lake Bangweulu, are discussed. It is concluded that, on the evidence offered by this work, biological utilisation appears to be adequate and that the low productivity of Lake Bangweulu must be related to edaphic factors.Field work was carried out while with The Joint Fisheries Research Organisation, P. O. Box 48, Samfya, Northern Rhodesia. (New Zambia).     

The diet of largemouth bass, Micropterus salmoides, in Lake Naivasha, Kenya

Lake Naivasha is a freshwater lake situated in the eastern rift valley of Kenya. Only five species of fish are present, all of which have been introduced. Of these, Oreochromis leucostictus, Tilapia zillii and Micropterus salmoides (largemouth black bass) support an important gillnet fishery with bass also being taken for sport. Until bass reached 260 mm f.l. they depended upon invertebrate food organisms. Thereafter crayfish, fish and frogs became increasingly important the larger the size of the bass. The most important invertebrate prey species was the water boatman, Micronecta scutellaris , followed by chironomid and culicid pupae. Zooplank-ton was consumed but only in large quantity by fish smaller than 80 mm. For bass over 260 mm the crayfish, Procambarus darkii , was the principal food. The largemouth bass in Lake Naivasha are generalized macro-predators, feeding principally on free-living animals of a kind most likely to be found in the littoral zones.     

Notes on the biology of Cancer bellianus (Brachyura, Cancridae) around the Canary Islands

Information on biometric and biological parameters of Cancer bellianus Johnson, 1861 (Crustacea, Decapoda, Brachyura, Cancridae) off the Canary Islands is given. Crabs examined were collected during experimental fishing surveys during 1974–1998. Carapace length, carapace width, total wet weight, sex and ovigerous condition were determined. This species was caught at depths from 153 to 750 m, the deepest ever recorded. Size frequency distributions were assembled and size-weight relationships were estimated by sex. Sex-ratio as a function of size and depth was determined. The size at first maturity was calculated by analysing the relative growth between the carapace length and the left chela width: 103.5 mm CL in males, 101.2 mm CL in females. Ovigerous females, egg size and fecundity estimates are reported apparently for the first time.     

Reproductive biology of the rock shrimp Sicyonia dorsalis (Decapoda: Penaeoidea) from the southeastern coast of Brazil

Summary

Sicyonia dorsalis is not commercially exploited in Brazil, but it forms a critical link in marine food chains by converting detritus food sources into microorganism biomass that is available for higher trophic levels. We examined the reproductive biology of this species, sampled for five and a half years in a tropical locality, the southeastern coast of São Paulo (23° S), Brazil. Monthly samples were taken from January 1998 to June 2003 at depths of 5 to 45 m. Degree of ovarian development was used to examine breeding in adult females. Recruitment was estimated by changes in proportion of individuals in juvenile size classes of carapace length (CL #8.2 mm) in relationship to the total number of individuals. The largest immature female measured 9.2 mm CL, but 75% of females were smaller than 7.3 mm CL. The largest immature male measured 6.8 mm CL. The relative frequency of reproductive females was negatively correlated with the relative frequency of recruitment (p <0.001). Reproductive females were found in every season, with peaks in December-February following the recruitment peak in March-June, and a second peak of spawning in May-July and of recruitment in September-November. The continuous reproductive pattern observed for S. dorsalis, combined with the hypothesis that during spring and summer the phytoplankton production is higher, when the South Atlantic central water mass intrudes into the region during upwelling events, suggests that food availability for protozoeal and mysis larvae may be an important selective factor shaping the seasonal breeding pattern for S. dorsalis. The classical paradigm of continuous reproduction at lower latitudes, with increased seasonality of the breeding period at higher latitudes, seems to be valid for this species.     

Nest defense and aggressive interactions between a small benthic fish (the johnny darter Etheostoma nigrum) and crayfish

Synopsis Aggression by nest-guarding male johnny darters, Etheostoma nigrum, against intruding crayfish was investigated in laboratoy experiments and field observations. In the laboratory, darter success in chasing crayfish, Orconectes rusticus, from the nest site was inversely related to crayfish size. Small crayfish (less than 15 mm carapace length) were routinely evicted from the nest area by nips directed at the posterior end of the abdomen. Although such aggressive behavior was less successful against larger crayfish, even the largest crayfish tested (carapace length 30–32 mm) were chased from the nest area in 33% of the trials. Those large crayfish that entered nests often remained despite repeated attacks by the male johnny darter and egg predation was observed. In a small Ohio stream, openings to johnny darter nests were generally between 7 and 13 mm. Thus crayfish with a carapace height greater than 13 mm (corresponding to a carapace length greater than 29 mm) would not be able to enter johnny darter nests. In field observations, male Johnny darters successfully defended nests against another crayfish species (Orconectes sanborni, carapace length 12–29 mm). Together, aggressive behavior and small size of nest entrances allow the johnny darter to successfully reproduce in areas with abundant crayfish. The Unit is sponsored jointly by the United States Fish and Wildlife Service, The Ohio Department of NaturalResources, and The Ohio State University.     

Distribution and breeding biology of offshore cichlids in Lake Malawi/ Niassa

Synopsis Lake Malawi/Niassa is the second largest rift valley lake in Africa, with an area of 28 800 km², and an average and maximum depth of 292 m and>700 m, respectively. The lake is well known for the great diversity of fish occurring in the inshore zone. However, the offshore fish community is poorly documented. To rectify this, regular sampling was undertaken over two years, using trawl and gillnets at six offshore locations. This paper reports on the species composition, spatial distribution and breeding biology of the dominant cichlids species from the offshore pelagic zone. Cichlids formed approximately 88% of the offshore fish biomass. Most abundant were two species of zooplanktivores in the genus Diplotaxodon that made up 71% of the offshore fish biomass. An undescribed species, given the cheironym D. bigeye, was mainly found at a depth of 220 m during the day, but moved into near surface waters at night when the moon was full. This species was absent from the shallow regions of the lake. The most abundant offshore species was D. limnothrissa, which was distributed evenly throughout the lake to depths of 220 m. A less common offshore zooplanktivore was Copadichromis quadrimaculatus that formed 5% of the biomass and was confined to the upper 100 m of the water column. The main piscivores were in the genus Rhamphochromis and formed approximately 10% of the offshore fish biomass. The two dominant taxa were R. longiceps and the large Rhamphochromis group, and both were more common in the southern half of the lake. The former occurred mainly in the upper 100 m of the water column and the latter mainly at depths of 100–150 m. The length at maturity and fecundity for the dominant offshore species were estimated and seasonal breeding cycles determined from gonad activity and gonado-somatic indices.     

Reproductive biology of the South West Atlantic marbled sand skate Psammobatis bergi Marini, 1932 (Elasmobranchii, Rajidae)

The reproductive biology of Psammobatis bergi was investigated based on 92 males and 136 females skates taken from the coastal bottom trawl fishery at Puerto Quequén, Argentina. The relationship between total body mass and total length (TL) was not significantly different between sexes, but females were heavier than males. Minimum length at maturity in males was 451 mm TL with a length ratio of 74%, whereas females were 415 mm TL with a length ratio of 74%. TL at which 50% of males were mature was 457.6 mm (75.6% of the largest male) and for females was 441.6 mm (79.1% of the largest female). The results indicate a continuous reproductive cycle during the year, with a maximum number of females carrying egg cases in warmer seasons.     

Feeding of the exotic Louisiana red swamp crayfish,Procambarus clarkii (Crustacea,Decapoda), in an African tropical lake: Lake Naivasha,Kenya

The Louisiana red swamp crayfish, Procambarus clarkii, has had a major impact on aquatic ecosystems in Europe and America where it has been introduced for human consumption. In Lake Naivasha, where it was introduced in 1970, it is suspected of causing the complete disappearance of native floating-leaved and submerged plants by 1982 and again by 1996; recovery of submerged plants occurred in between, concurrent with a decline in P. clarkii. Examination of the feeding of P. clarkii by microscopic analysis of gut contents collected from the lake confirmed information from both its native and exotic ranges; that it is an omnivore with green plants and insects the predominant items recognised. Feeding experiments confirmed this omnivory, with a preference from herbivory over carnivory. They further showed the importance of native plants as opposed to exotic water hyacinth Eichhornia crassipes. It is concluded that P. clarkii could well have accounted for the observed elimination of native plant species in Lake Naivasha; the cyclical nature of populations of submerged plant species and of P. clarkii in inverse proportion to each other lead us to hypothesise that P. clarkii is a `keystone' species in the lake ecosystem.     

Daily egg production rate of the planktonic calanoid copepod Acartia lilljeborgi Giesbrecht in the Cananéia Lagoon estuarine system,São Paulo,Brazil

Seasonal variation in daily egg production rate of the planktonic calanoid copepod Acartia lilljeborgi Giesbrecht in relation to temperature, salinity and chlorophyll a concentration was studied in the Cananéia Lagoon estuarine system, from March 1995 to January 1996. Recently captured A. lilljeborgi adult females were individually incubated in bottles filled with surface water screened through a 40-m mesh, containing a natural assemblage of phytoplankton in the laboratory, at temperatures corresponding to ambient. Daily egg production rate ranged from 13.8±3.5 to 66.8± 15.1 eggs female^–1 d^–1 (mean ± 95% CL). The mean and maximum rates of daily egg production increased with temperature from 19.5 to 25.2 °C but then decreased with further increase in temperature at 28.4 through 29.1 °C, attaining the highest rates at approximately annual mean ambient water temperature (ca. 24–25 °C). The egg production rates increased linearly with chlorophyll a <40 m fraction. Hatching success varied from 68.6 to 91.9%. Cannibalism varied from 1.4±0.7 to 7.1±3.3 nauplii female^–1 d^–1 (mean ± 95% CL). These results suggest that water temperature and phytoplankton concentration are important factors affecting the egg production rate of A. lilljeborgi in the Cananéia Lagoon estuarine.     

Potential errors in fiber length measurements resulting from lever arm rotation during mechanical testing of muscle cells

In single muscle cell preparations fibers are often suspended between connectors, extending perpendicularly from a force transducer, and the lever arm of a torque motor. The fiber does not move along a horizontal plane when shortened or lengthened by lever arm rotation. An error from the true length (TL) is introduced if the expected length (EL) is calibrated along this horizontal optical plane. Lever arm length (LAL), initial fiber length (FL(i)), connector length (CL), and the magnitude of EL all contribute to this error. A mathematical model was used to determine the TL during shortening (0.96-0.80 FL(i)) and lengthening (1.10-1.50 FL(i)) at a constant LAL of 13.6mm. CL had the greatest impact on error. For FL(i) = 2mm at the longest CL modeled (15 mm), an expected shortening of 0.20 FL(i) produced a true shortening of ～ 0.17 FL(i), and an expected stretch to 1.50 FL(i) resulted in a true stretch to almost 1.60 FL(i). Under these conditions, the true sarcomere length would be 4% and 6% longer than expected during shortening and lengthening, respectively. Because of their non-linear nature, length errors at long CL's may result in an over-estimation of unloaded shortening velocity during slack tests and a left-ward shift in the passive tension-fiber length relationship at long fiber lengths. Measurement errors decreased dramatically with shorter CL's, becoming negligible (<1%) at CL = 3mm. We recommend that investigators keep CL as short as possible. Alternatively, we provide a method for adjusting the magnitude of the EL to yield a desired TL.     

Reproductive biology ofSarotherodon mossambicus,an introduced species,in an ancient man-made lake in Sri Lanka

Synopsis The reproductive biology ofSarotherodon mossambicus (Peters), a species exotic to Sri Lanka, was studied in Parakrama Samudra — an ancient man-made lake. Females outnumbered males by approximately 2 to 1, but the predominanace of females tended to decrease with increasing size. Males mature at a length of 27.5 cm and females at a length less than 15.0 cm.S. mossambicus breeds throughout the year with four possible peak periods, which coincide with the tailend of the monsoon and intermonsoon rains. The egg diameter distribution indicates the presence of reserve oocytes and yolked oocytes, the latter falling into a single mode between 1.2 to 3.6 mm. Fecundity varied between 360 and 1775 for fish ranging in length from 20.0 to 31.9 cm and 145 to 538 g in weight. The diameter of nests increased with depth up to 60–65 cm. Nests were not found in depths over 90 cm.     

Why egg-caring males of Isaza (<Emphasis Type="Italic">Gymnogobius isaza</Emphasis>, Gobiidae) refuse additional females: preliminary field observations

Like many other gobies, males of the Isaza goby, Gymnogobius isaza endemic to Lake Biwa, Japan, conduct parental care of eggs at nests, and females are likely to choose mates while visiting nests. The reproductive strategy should induce polygyny, but Isaza males never accept additional females in one breeding cycle. Sampling data of broods indicated that the egg mass areas were much smaller than the nest sizes, suggesting that nest size is not the limiting factor in obtaining further eggs from additional females. The brood size greatly decreased as the duration of care progressed. Few individuals including caring males ate eggs, and heterospecific egg predators were rarely observed. Sixty percent of egg masses at the middle stages of egg development were infected with aquatic fungi, some being covered with a fungus mat that drastically reduced survivorship. Infected egg masses contained more eggs than non-infected ones at the same stage, indicating that large egg masses are prone to be frequently destroyed by fungi. It is likely that the activity of parental males is lowered during the long care periods at low water temperature in early spring. Such lowered activity of caring males might be responsible for infections in large broods that would have needed more care. We propose the hypothesis that male rejection of additional females may be related to optimal brood size, which will be less susceptible to fungus infection and produce more hatching young than otherwise. This hypothesis will explain not only male avoidance of additional females but also some unique reproductive behaviors of this fish such as some females spawning of a portion of of the mature eggs in one nest.     

On the Life History of a Cyprinid Fish, Labeo cylindricus

Aspects of the life history of Labeo cylindricus in Lake Chicamba, a man made hydroelectric dam in central Mozambique were investigated. L. cylindricus was found to be a potadrometic, synchronous spawner concentrating in river mouths prior to migrating up flowing rivers in January to spawn. Length-at-(50%)-maturity was attained at a fork length (FL) of 96mm for males and 98mm for females, both within their first year of life. The adult sex ratio was found to be female dominated at 1 male:1.63 females. Scales were used to age the species, with two growth checks deposited annually. Growth was rapid and was best described by the von Bertalanffy growth model as L _t =224.2(1–e^{-0.66(r+0.03)})mm FL. A maximum age of 4 years was observed for L. cylindricus with the largest male and female measuring 210mm FL and 235mm FL, respectively. The rate of natural mortality was estimated to be extremely high at 1.93year^-1 using length-converted catch curve analysis and is possibly a response to heavy predation by the introduced piscivore Micropterus salmoides.     

'Leaves and eats shoots': direct terrestrial feeding can supplement invasive red swamp crayfish in times of need

We used stable isotope analyses to characterise the feeding dynamics of a population of red swamp crayfish in Lake Naivasha, Kenya, after the crash of submerged macrophytes and associated macroinvertebrates, and during a natural draw-down of the lake water level. We expected a heavy reliance upon a diet of detrital matter to sustain the population as a consequence, and indeed, for the majority of the crayfish population caught from the lake, we saw a concomitant shift in isotopic values reflecting a dietary change. However, we also caught individual crayfish that had occupied the footprints of hippopotamus and effectively extended their range beyond the lake up to 40 m into the riparian zone. Isotopic analysis confirmed limited nocturnal observations that these individuals were consuming living terrestrial plants in the vicinity of the footprints. These are the first empirical data to demonstrate direct use of terrestrial resources by an aquatic crayfish species and further highlight the traits that make red swamp crayfish such opportunistic and successful invaders.     

Reproductive biology, length-weight relationship and relative condition of Tilapia leucosticta (Trewavas) in Lake Naivasha, Kenya

In Lake Naivasha Tilapia leucosticta (Trewavas) spawns throughout the year. Males attain maturity at 180 mm and females at 160 mm total length. Males predominate over females in the catches (sex ratio 1-00 : 0-51). Fecundity ranged from 320 to 1328 eggs with an average of 751. The relationship between fecundity (F) and total length (L), body weight (W) and gonad weight (GW) is:
The length-weight regression coefficient is near to the cube. There is little seasonal fluctuation in relative condition of the fishes.