Reproductive biology of the lanternfish Benthosema pterotum from the Indian Ocean

Samples of Benthosema pterotum (Alcock) were obtained from the Arabian Sea (1976, 1979, 1981, 1983, 1984), off Mozambique (1978) and from the Bay of Bengal (1979). The sexual maturity stages are described. For females, the size of the largest oocytes was found to be most useful for size of the largest oocytes was found to be most useful for assessing maturity. Mature and spawning fish were found in all seasons. Samples from November 1983 differed from all others in having very few mature females. A few apparently spent fish were observed in July to August 1979 and November 1983. Some females mature at 25 mm and males at 20 mm, whereas others can still be immature at 45 and 40 mm, respectively. Of the total number of stations, four had significantly more males than females, twelve significantly more females, and forty-seven displayed no difference in the sex ratios. The vertical migration of the mature and spawning fish did not differ significantly from that of other individuals. Batch fecundity ranged from ca. 200 to 3 000 eggs fish ranging from 27 to 52 mm, relative fecundity from ca. 2 000 to 7 000 eggs g^-1 maternal dry weight. There are indications that B. pterotum spawns only once, but no firm conclusions could be drawn.     

Transformation of food in the fish Megalops cyprinoides

Comparative studies on feeding, digestion, absorption and conversion have been made in the fish Megalops cyprinoides fed with mosquito fish, Gambusia affinis, and prawn, Metapenaeus monoceros, (Pandian, 1967). Feeding as well as digestion rates are faster in individuals fed with Gambusia than in those fed with prawn. The extent of the differences in food intake is more pronounced in smaller individuals than in larger ones. The prawn exoskeleton prolongs the duration of digestion and thus further reduces rate and amount of food intake. Changes in food quality do not affect absorption efficiency. Both, rate and efficiency of food conversion, are higher in M. cyprinoides fed with Gambusia than with prawn.     

Effects of feeding rate on conversion efficiency and chemical composition of the fish Tilapia mossambica

Average daily rations of 14, 35 or 58 mg Tubifex tubifex worm per gram of the fish Tilapia mossambica Peters represent maintenance, optimum or maximum feeding levels. At these levels, conversion efficiency (K ₁) is 5,9 or 24%. An amount of 65 mg worm/g fish/day, when fed under experimental conditions, is converted with the poorest conversion efficiency (4%). Test individuals fed at 11 to 49 mg worm/g fish/day show a decreasing trend in water content (78.1 to 74.8%), and an increasing trend in fat content (32.1 to 44.2%). Below or above this feeding rate range, water content increases, while fat content decreases. The range of individual variations in fat content is nearly 3 times greater than that of ash and 15 times greater than that of water. Test individuals starved for 60 days lose 2.1 mg dry body weight/g/day. This loss is contributed by calorifically equivalent amounts of fat and protein. The endogenous loss of nitrogen by these individuals averaged 0.18 mg N/g body weight/day.     

Association patterns of sailfin mollies (Poecilia latipinna): alternative hypotheses

Individuals may associate with each other due to a variety of selective forces, such as intra- and intersexual selection, and conspecific recognition. Previous studies have concluded that mate choice governs association behavior in polygynous species of fish. I examined whether mate choice underlies the preference for larger individuals by examining preference for association (time spent in proximity to a fish) not only between opposite-sex individuals but also between same-sex individuals of the live-bearing sailfin molly (Poecilia latipinna). Males and females from three size classes were tested with a large and a small object fish of the same and opposite sex. Females preferred to associate with larger over smaller males. Males also preferred to associate with larger over smaller females, as expected. The same female and male test fish also preferred to associate with larger over smaller fish of the same sex. Moreover, females demonstrated no significant difference in their strength of preference (large–small) when offered males or females. The same held true for males. When males and females were subsequently tested with one large male and one large female, females tended to prefer large males while males showed no significant preference for association based on sex. In another experiment, females were tested with a large female and a small male, and significantly preferred the former. These findings suggest that association patterns may have arisen under a variety of conditions, such as predation pressures, shoaling behavior, and associative preference behavior. The assumption that association behavior is a uniformly sufficient predictor of mate choice in fish needs to be re-examined for P. latipinna and other species. Received: 6 November 1998 / Received in revised form: 12 May 1999 / Accepted: 12 May 1999     

Structure of and energy reserves in the liver of wild and cultured yellowtail flounder,<Emphasis Type="Italic"> Limanda ferruginea</Emphasis>

Knowledge of the structure and energy reserves, in the liver of commercially important fish species, is important in understanding metabolic processes and in assessing the impact of potential environmental physical and chemical stressors in both wild and cultured stocks. The present study investigated the microscopic morphology and histochemistry (total and neutral lipids, glycogen) of liver tissue of wild (3 ⁺) and cultured (1 ⁺) sexually immature female and male yellowtail flounder ( Limanda ferruginea Storer), sampled in late April 2001. Hepatosomatic indices [HSI: (liver weight/body weight-liver weight)×100] of cultured fish were significantly higher than those of wild fish. Females in the cultured group had significantly lower HSIs than males. The liver of both wild and cultured L. ferruginea was interspersed with pancreatic tissue. The main components of the liver tissue were irregular cords of hepatocytes arranged in tubules which surrounded vascular sinusoids. The hepatocytes contained an abundance of lipid, much of which appeared to be neutral lipids, in both sexes of the cultured fish. Total and neutral lipid droplets were larger, and the area occupied by these droplets was significantly greater in both cultured females and males compared to the wild fish, suggesting lipidosis in the cultured fish. In the cultured fish these differences were sex-dependent, the females having significantly more total and neutral lipids in hepatocytes than the males. This suggests a potentially greater storage capacity in females and/or a higher lipid metabolism in males. There were no statistically significant differences in glycogen content between the cultured and wild fish, or between the sexes in both sampling groups.     

Do cod form spawning leks? Evidence from a Newfoundland spawning ground

Catch and acoustic telemetry data were used to test three predictions of lekking behaviour in Atlantic cod (Gadus morhua L.) at a small-scale spawning ground (∼25 km²) in Placentia Bay, Newfoundland: (1) that cod form male-skewed aggregations during spawning; (2) spawning arenas occur at consistent sites; and (3) on the arenas, there will be higher proportions of spawning fish. Forty-two fishing sets from 1998 to 2003 indicated male-skewed sets early in the spawning season (April) in 5 of 6 survey years. Male-skewed sets were consistently distributed at depths < 50 m and mostly in one part of the ground. The proportions of spawning females and spent males were significantly higher in male-skewed sets, whereas sets with equal sex ratios had significantly higher proportions of immature males and spent females. In addition, cod of both sexes were significantly larger in male-skewed sets. Telemetric tracking of 25 cod in 2002 and 2003 (12 males, 13 females) indicated that both males and females were highly mobile while present on the spawning ground. Overall, our results add support to the hypothesis that cod employ a lekking mating system.     

Social and ecological influences on activity budgets of vervet monkeys,and their implications for group living

Summary Activity patterns were documented over a 20-month period in six groups of vervet monkeys (Cercopithecus aethiops) in Amboseli National Park, Kenya. Group size varied both among groups and within groups through time. The home ranges of two groups were located in Acacia xanthophloea habitat whereas those of four adjacent groups were located in A. tortilis habitat. Repeated measures analysis of variance, three-way analysis of variance, and meta-analysis of group size effects were carried out on feeding, moving, resting, scanning, allo-grooming, and other behavior. Time spent feeding varied seasonally, peaking during periods when A. tortilis seeds were eaten. However, time spent feeding did not vary within or among groups, or between habitats, males and females, or dominants and subordinates. Males spend more time scanning and less time allo-grooming than females, and high-ranking individuals of both sexes spent more time scanning than low-ranking individuals. Among females, subordinates spent more time moving, whereas among males, dominants spent more time moving. Groups living in A. xanthophloea habitat spent more time moving and allo-grooming than groups in A. tortilis habitat but this may have been confounded by the fact that these two groups were on average larger than the others. Significant differences in activity budgets among groups demonstrate that activity patterns observed in one group are not always readily generalized to other groups even when they come from the same population. Group size analyses examined potential costs and benefits of group living. Increased intragroup competition, measured by time spent moving and feeding, was only weakly evident in larger groups. Individuals in larger groups allo-groomed more than individuals in smaller groups. Self-grooming also increased in larger groups. Individuals in larger groups spent less time scanning than individuals in smaller groups, but there was more scanning per group in larger groups than in smaller groups. Correspondence to: L.A. Isbell     

Social organization and nest co-occupancy in Peromyscus californicus,a monogamous rodent

Summary Home ranges, social organization, and nest co-occupancy of Peromyscus californicus were studied using radiotelemetry at the Hastings Natural History Reservation, California. Mated pairs were ascertained by the transfer of fluorescent pigments from lactating females to putative fathers. Mated pairs had largely overlapping home ranges that were not statistically distinguishable, whereas adjacent adults had mostly exclusive, statistically distinguishable home ranges. There was no difference in the mean home range of males and females, but mated females tended to have smaller ranges than their mate. Home range size was extremely variable (range: 150–3788 m²) and averaged 1161 m² across all individuals. Male home range size was inversely correlated with population density, suggestive of a social influence on home range. Putative fathers spent comparable amounts of time to females in the nest — presumably caring for the young — which supports previous laboratory reports of paternal care in this species. All data collected in this study are consistent with previous suggestions that P. californicus live in semi-permanent family groups and are monogamous. Offprint requests to: D.O. Ribble     

The dual functions of sea urchin gonads are reflected in the temporal variations of their biochemistry

Fatty acid analyses are emerging as a powerful technique to probe trophic interactions between organisms. In this paper, the application of both this procedure and gonad index (GI) determination on two populations (intertidal and subtidal) of the echinoid Psammechinus miliaris is reported. The investigation spanned the 3-month spawning period of Scottish west coast populations. In both populations a progressive decrease in the GI was found, coupled with an increasing maturity stage (from mature to spent). Sexual maturation and decrease in GI was synchronous between the two populations. In conjunction, there were distinct changes in gonad biochemistry. Differences in the fatty acid composition of the gonad reflected the changes in sexual maturation. Mature males and females had significant differences in the fatty acid composition of their gonads, whereas post-spawned individuals showed no gender differences. Male urchins had higher levels of polyunsaturated fatty acids (PUFAs) compared to females, and there was a dramatic reduction in the fatty acids 22:6(n−3) and 20:5(n−3) with increasing maturity stage. Using multivariate statistical techniques, these changes in the fatty acid composition of the sea urchin gonad were linked to habitat related diet differences combined with gender differences. These changes in the fatty acid signatures clearly reflect the dual function of the gonad as both a nutrient store and a reproductive organ.     

Large male advantage for access to females: evidence of male-male competition and female discrimination in a territorial salamander

Summary In the natural habitat visited in this study, adult male red-backed salamanders (Plethodon cinereus) found near females were significantly larger than adult males found alone; there was no evidence for size assortative associations. Previous research has indicated that females associate preferentially with males that occupy high quality territories and that larger individuals are more successful at obtaining higher quality areas. In laboratory experiments, when resource quality was held constant and males were restrained so that male-male interactions were prohibited, females discriminated behaviorally between large and small males by spending more time visually and chemically assessing larger males and more time apparently attempting to leave the chamber when near smaller males. Females were found near the larger males at the end of the trials significantly more often than predicted by chance. In a separate experiment in which only females were restrained, larger males spent significantly more time in aggressive postures when paired with smaller males than when alone with the female. Smaller males spent significantly more time in submissive postures when paired with larger males and more time near the female when alone. Therefore, large body size of males may positively affect both intra- and intersexual interactions and, ultimately, mating success of male P. cinereus.     

Tissue,ontogenic and sex-related differences in δ<Superscript>13</Superscript>C and δ<Superscript>15</Superscript>N values of the oceanic squid <Emphasis Type="Italic">Todarodes filippovae</Emphasis> (Cephalopoda: Ommastrephidae)

Stable isotopes are increasingly used in the study of trophic interactions of many aquatic animals and most recently cephalopods. To evaluate the application of the method to squids, it is important to assess isotopic differences among and within consumer tissues that may confound the resolution of ecological relationships. Inter- and intra-tissue isotopic variation was examined in 55 individuals of the oceanic squid Todarodes filippovae that were collected at the beginning of April 2000 in the southwestern Indian Ocean (between 44°S, 76°E, and Saint Paul and Amsterdam islands, 38°S, 78°E). Delipidated soft tissues (mantle, arm, buccal mass, gill and reproductive organs) showed small δ¹³C and δ¹⁵N differences, which were probably tissue-specific. A lower carbon value was observed in the digestive gland as a consequence of incomplete lipid removal. Hard tissues, such as beaks and gladii, had lower ¹⁵N values than soft tissues, which can be explained by the presence of chitin, a ¹⁵N-depleted molecule. Females (n = 38) and males (n = 17) had identical δ¹³C values, but females showed higher δ¹⁵N values than males. The difference was size-related rather than sex-related, however, as females were generally larger than males. A comparison of similar-sized females and males produced identical nitrogen values. These data suggest dietary shifts from lower to higher trophic levels during growth, because δ¹⁵N values of large T. filippovae were much higher than that of small specimens. As expected, nitrogen values of lower beaks and gladii of large squids increased from the oldest to the most recently formed region, reflecting the progressive growth of chitinized tissues in parallel with dietary changes. Sequential sampling along the growth increments of squid beaks and gladii can likely be used to produce a chronological record of dietary information throughout an individual’s history.     

Behavioural plasticity in a large marine herbivore: contrasting patterns of depth utilisation between two green turtle (Chelonia mydas) populations

We used time-depth recorders to measure depth utilisation in gravid green turtles (Chelonia mydas) during the internesting period at northern Cyprus (Mediterranean), a nesting area where individuals feed, and at Ascension Island (mid-Atlantic), a nesting area where individuals fast. There were contrasting patterns of depth utilisation between the two sites, illustrating that the behaviour of this species is shaped by local conditions. For example, the amount of time spent shallower than 4 m was 90% at Cyprus but only 31% at Ascension Island, and there was a clear difference between the mean depth at Cyprus (2.7 m, n=9 internesting intervals) versus Ascension Island (9.5 m, n=6 internesting intervals) (t ₅=5.92, P=0.002). At Cyprus, turtles spent the greatest percentage of their time at very shallow depths, where surveys reveated a high abundance of seagrass on which this population feeds. In contrast, the deeper distribution at Ascension Island may reflect the preferred depth for resting on the seabed. Published online: 23 July 2002     

A further contribution to the study of fish populations by capture-recapture experiments

In capture-recapture experiments, fish populations can be studied by two different sampling procedures. In both procedures, tagged fish are released on capture, but untagged fish are in one procedure released after tagging, in the second procedure they are retained. Using the two sampling techniques, Rafail (1971a,b) gave expressions for the estimation of an assumed constant (C) of proportionality between probabilities of capture of tagged to untagged fish which are simplified here to forms easier for calculation. The estimation of this constant (C) aids in estimation of abundance and mortality rates of untagged fish which are assumed to differ from those of tagged fish.     

Ontogenetic,social, spatial and seasonal variations in condition of the reef herbivore Sparisoma viride

We studied the condition of stoplight parrot-fish, Sparisoma viride, collected from the fringing reef of Bonaire (Netherlands Antilles) between March 1987 and October 1991. To this end, we compared length-weight relationships using analysis of covariance. The condition of different life phases [juveniles, initial phase (IP) and terminal phase (TP) adults] and social categories (territorial and group adults) is compared in different seasons, taking into account spatial variability along a depth gradient. Variations in condition are related to differences in behaviour, the use of space and the distribution of food. The average length-weight relationship of fish with empty guits is described by the equation: W _Empty=9.115x10^-6xFL ^3.140 (n=386, R²=99.82%, W in g, FL in mm). Territorial TP males were found to be in poorest condition, whereas (sexually inactive) group TP showed the best and IP fish an intermediate condition. These differences are ascribed to varying investments in territory defence and reproduction, which affect condition more than the vertical distribution of food. All categories were in minimum condition between May and July, the season with longest day lengths and increasing water temperatures. This seasonal effect cannot be ascribed to increased reproductive effort and suggests that the higher energetic demands due to the longer active period of fish are not completely met by increased food uptake. It is inferred that food may be a limiting factor at times.     

Growth,production and energy transformations in the salt-marsh killifish Fundulus heteroclitus

Populations of Fundulus heteroclitus (L.) at the beginning of a growth season in a New England salt marsh consist of 3 yearly age classes, with the 1-year-old class contributing most of the biomass. Calculation of production rates revealed that the young fish were the most active part of the population and that females were more productive than males. The entire population spent equal amounts of energy in growth and in metabolism. Including the young of the year, we obtained total production of 160 kg dry weight/ha, a value among the highest obtained for natural fish populations. About 5 to 15% of the production is available to predators. Rates of food consumption by F. heteroclitus are high enough to turn over the population of prey relatively often. Popululations of F. heteroclitus are thus capable of exerting an important influence on the abundance and distribution of their prey.Contribution No. 3721 from the Woods Hole Oceanographic Institution.     

Fecundity of the Argentinean mackerel Scomber japonicus marplatensis

Research on the spawning and fecundity of the Argentinean mackerel Scomber japonicus marplatensis was carried out during the spawning season 1966/67. The purpose of the present study was to obtain data for the estimation of the number of eggs which can be produced and spawned by one female of a known size, during one season of reproduction: 152 females were studied. All yolked ova of the biggest size group were taken into consideration. On the basis of the relatively short spawning season, the great homogeneity in meristic characteristics, and histological examination, it is assumed that the Argentinean mackerel spawns once a year. The fecundity of the smallest female of 315 mm in total length was calculated to be 101,859 eggs, and the total number of yolked ova 181,000; for the biggest female of 470 mm in length, 522,370 and 853,500, respectively. The relation fecundity/length and fecundity/weight is almost rectilineal. The equations: F=8.17 ^0.008L for fecundity/length relationship, and F=0.42 W ^1.043 for fecundity/weight relationship, were calculated. Prediction curves were established in each case. It would appear that the fecundity of smaller fish is associated more with length, and the fecundity of bigger fish more with weight. Large differences in fecundity of specimens of the same size were observed.Communicated by M. Vannucoi, So Paulo     

Elemental distribution in relation to skin necroses of marine flatfishes from the english channel

It has been suggested that industrial waste discharges are associated with the occurrence of fin damage and skin lesions. A mixed population of diseased and healthy blatfish consisting ofLimanda limanda, Pleuronectes platessa, Platichthys flesus andSolea solea were collected from an industrialised area (Calais, France) and were compared with diseased and healthyl. limanda caught in a non-industrialised area (Brixham, England). Analysis of skin samples from necrosed and healthy fish by X-ray microanalysis and atomic absorption spectroscopy has shown that no elemental accumulation occurs either in necrosed fish, or fish from an industrialised area. The fish from Calais were heavily infested with the ectoparasitic copepodLepeophtheirus pectoralis (O.F. Müller) and, although few were found on fish from Brixham, it is unlikely that this infestation was related to the discharge of industrial effluents.     

Use of blubber levels of progesterone to determine pregnancy in free-ranging live cetaceans

We tested the possibility of measuring progesterone levels in bubbler samples collected from free-ranging live bottlenose dolphins (n = 11) and long-finned pilot whales (n = 2) as a tool to evaluate the pregnancy status of individuals. Samples were collected during January 2004 and September–October 2005 in the Strait of Gibraltar and Gulf of Cadiz and used for sex-determination by genetic methods (skin samples) and for quantification of progesterone levels by enzyme immunoassay. Photo-identification tracking of females after taking the biopsy was used to observe the presence of newborns and, in this way, to determine if the female was pregnant at the time of sampling. Mean progesterone levels from pregnant bottlenose dolphins (n = 2) were around 9 times higher than those from non-pregnant females (n = 9), with no overlap between concentration ranges demonstrating that this method could constitute an effective tool for determining pregnancy in wild populations of bottlenose dolphins and other cetacean species.     

Seasonal changes in the diet of a critically endangered seabird and the importance of trawling discards

Pelagic seabirds obtain food from oceans where the availability of their prey changes rapidly both seasonally and spatially. Here, we investigated changes in the trophic habits of the critically endangered Balearic shearwater (Puffinus mauretanicus) through the breeding season and tested for dietary differences between sexes and age classes. We analysed δ¹⁵N and δ¹³C values in blood of adults during the pre-incubation, incubation and chick-rearing periods and of their chicks. Using a two-isotope mixing model, we estimated dietary contributions based on isotope values from potential prey species which included small pelagic species available naturally and demersal fish species available only from trawling discards. Balearic shearwaters showed clear isotopic and dietary variation through the breeding season. During pre-incubation, breeding adults appeared to exploit demersal fish, whereas during the incubation and chick-rearing period, they fed mainly on pelagic anchovies (Engraulis encrasicolus) and pilchards (Sardina pilchardus). Similarly, chicks were fed mainly with anchovies, a resource with a high energetic value. This variation in the dietary habits of adult shearwaters during the breeding season was probably related to both natural and fishery-induced seasonal changes in the availability of potential prey species within their main feeding grounds. However, changes in the nutritional requirements of the shearwaters could also play an important role. Indeed, diet differed between sexes during pre-incubation: females fed less on trawling discards and more on small pelagic fish than males. This sexual segregation in diet could be the consequence of higher nutritional requirements of females during this period. Our study reveals the differential importance of both trawling discards and small pelagic fish species for a pelagic seabird depending on the breeding period and illustrates the importance of considering the entire breeding season when making inferences about the importance of specific prey in seabird dietary studies.     

A stereoscan electron microscope study of male reproductive characters in the Jaera albifrons group of species (Crustacea: Isopoda)

The male secondary sex characters of Jaera albifrons Leach, Jaera ischiosetosa Forsman, Jaera praehirsuta Forsman and Jaera forsmani Bocquet are described with the Stereoscan electron microscope (S.E.M.). These characters, which are present on the peraeopods, are the only means of identification for these Jaera species which together form the Jaera albifrons group (Isopoda, Asellota). The male praeoperculum (modified, fused, first pair of pleopods) and appendix masculinae (modified endites of the second pair of pleopods) have also been studied with the S.E.M. and possible functions of the various sex characters are discussed. Both the male operculum and appendix masculinae are similar for each species, suggesting that copulation with females of a different species is anatomically possible. The fact that hybrids are rarely collected in ecological investigations is discussed with reference to the present known information. Two methods of copulation for the members of this group have been proposed and these are discussed. A method of sperm transfer along the male operculum is outlined.