Growth of Odontesthes bonariiensis (Atherinidae) larvae feeding on suboptimal zooplankton densities

Synopsis In this study we investigate the effect of food availability (zooplankton biomass) on the growth of Odontesthes bonariensis (Atherinidae) larvae. The larvae were stocked in four 45 m² outdoor tanks at relatively high densities (100 and 200 larvae m^–2). Because of the high stocking densities, the zooplankton biomass was depleted in all tanks. However, the patterns of food limitation, and particularly periods of severe food shortage, differed in tanks stocked at different densities. We could therefore, observe the effect of food limitation in larvae that differed in weight and age. The effects of variables suspected to influence O. bonariensis growth rates (age and weight of larvae, available zooplankton biomass, mean individual weight of available preys, total ingested prey weight, and mean weight of ingested preys) were investigated using standard multiple regression methods, and a model assuming: (1) an allometric relationship between maximum growth rates and weight of larvae, and (2) an inverse relationship between growth depression and the available zooplankton biomass. Both methods were consistent in showing that only the weight of larvae, and the availability of zooplankton prey had significant effects on the growth of O. bonariensis. The model's results additionally suggest that, if the observed growth rates are scaled by the maximum growth rate corresponding to the larva weight, the effect of zooplankton biomass is largely independent of age and weight of larvae.     

Ontogenetic shifts in the diet ofGalaxias maculatus (Galaxiidae) andOdontesthes microlepidotus (Atherinidae)

Synopsis The feeding habits ofGalaxias maculatus (Galaxiidae) andOdontesthes microlepidotus (Atherinidae) larvae and juveniles were studied in an Araucanian lake of Argentina. Fish specimens were grouped, on the basis of the percentage of each food category found in their gut, using multivariate methods. These groups of fishes showed significant differences in average total length. Positive correlations between prey size and fish length were also detected. Diet overlap between juvenileG. maculatus and juvenileO. microlepidotus was observed. We discuss the interaction between the two species and the role of functional capabilities for prey capture during these early life periods.     

Intralacustrine movements of Galaxias maculatus (Galaxiidae) and Ondontesthes microlepidotus (Atherinidae) during their early life history

Synopsis Galaxias maculatus and Odontesthes microlepidotus undertook significant habitat shifts in a small Araucanian lake during their early life history. After hatching in the littoral zone, free embryos migrate to the limnetic zone. Later, larvae return to the littoral. A third movement, littoral-limnetic, is suggested through acoustic records of fish in the limnetic zone which correspond with the growth curve of littoral sampled juveniles.     

Latitudinal differences in somatic energy storage: adaptive responses to seasonality in an estuarine fish (Atherinidae: Menidia menidia)

This study focuses on the seasonal accumulation and depletion of somatic energy in the Atlantic silverside (Menidia menidia), an annual estuarine fish. Previous research revealed that northern silversides are subject to strong size-dependent winter mortality, while southern fish suffer no appreciable winter mortality. To examine whether there was geographic differentiation in allocation strategies, we compared temporal patterns of energy storage and utilization among three populations along this gradient in seasonality. The comparative design used monthly or biweekly samples of fish collected in the wild, as well as samples of fish from each population reared in a common environment, where genetic differences can be clarified. Somatic energy stores were quantified via gravimetric analysis of neutral storage lipids and lean tissue. Analysis revealed that small individuals maintained relatively low levels of lipid reserves, which may account for their lower survival in winter. Wild fish in the north rapidly accumulated large somatic reserves, which were depleted over the winter and then increased again during the subsequent spring breeding season. In wild southern fish, relatively small reserves accumulated slowly until breeding commenced in the spring. The common-environment comparison of somatic storage patterns revealed a genetic basis for among-population differences in reserve accumulation rates, but no differences in the amount of reserves stored. We conclude that the overwinter depletion of somatic reserves has a significant selective impact on energy accumulation and allocation strategies in seasonal environments. Received: 1 November 1995 / Accepted: 13 September 1996     

Hepatocyte nuclear size and nutritional condition of larval pejerrey, Odontesthes bonariensis (Cuvier et Valenciennes)

This paper presents evidence that the size of the nuclei of parenchymal cells of the liver is correlated with the nutritional status of first-feeding pejerrey larvae, Odontesthes bonariensis (Cuvier et Valenciennes). Kariometry revealed that larvae which successfully began exogenous feeding maintained the large nuclear sizes attained during the period of endogenous feeding. In contrast, nuclei of fasted larvae shrank gradually and lowest values were attained before starvation death. The degree of shrinkage seemed to be dependent on rearing temperature; reduction in nuclear area was faster and more pronounced at higher temperatures. In addition, mean hepatocyte nuclear areas of larger as well as of triploid fish are presented. The results suggest that hepatocyte nuclear size might constitute an alternative indicator for the identification of starving condition in field larval specimens.     

The effect of starvation on the ultrastructure of the red and white myotomal muscles of the crucian carp (Carassius carassius)

Summary The effect of 16 weeks total starvation on the ultrastructure of the red and white myotomal muscles of the crucian carp (Carassius Carassius) has been investigated. In the white fibres the amount of myofibrillar material fell from 89.6% to 70.7% of the total fibre volume whilst in the red fibres the fall was from 72.2% to 70.3%. The sarcoplasmic reticulum appeared to have become swollen during starvation in both fibre types. In the white fibres the terminal cisternae of some triads seem to have fused. The volume of the red fibres occupied by mitochondria was reduced from 16.2 % to 5.9 %. The concentration of mitochondria in the white fibres was too low to detect any quantitative changes. A marked reduction in the amount of euchromatin material was observed in most white fibre nuclei and many red fibre nuclei. Many of the ultrastructural changes noted in the present study can be correlated with biochemical changes known to occur in the red and white myotomal muscles of fish during starvation. This work was supported by a grant from the Natural Environmental Research Council.     

Comparison of nutritional status of field and laboratory reared Balanus amphitrite Darwin (Cirripedia: Thoracica) larvae and implication of starvation

Experiments were carried out to evaluate the influence of rearing temperature and food concentration (20 and 30 °C, 1×10⁵ and 2×10⁵ cells ml⁻¹) on the starvation threshold and nucleic acid content of the larvae of Balanus amphitrite. The larvae were also field-reared using micro-enclosures. Laboratory-reared larvae were larger in size than the field-reared larvae. An increase in size, DNA content and instar index of the starved II instar larvae was observed indicating that the absence of food may not be fatal to this early instar. The temperature at which larvae were raised and the food concentration had variable influence on the capacity to withstand starvation. Exposure to increased temperatures during starvation eliminated the effect of doubling food concentration during their feeding period prior to starvation. The larvae reared at 20 °C had comparatively lower nucleic acid content. The laboratory-reared larvae had ca. 1.7 times greater RNA:DNA ratio than larvae raised at comparable temperature in the field.     

Reproductive behavior of the Atlantic silverside,Menidia menidia (Pisces,Atherinidae)

Synopsis The spawning behavior of the Atlantic silverside,Menidia menidia, was studied at two sites on the North Edisto River estuary in South Carolina. Prespawning schools moved back and forth along the shoreline as the time of high tide approached. Spawning runs took place in the upper intertidal zone at high tide.Spawning fish deposited their eggs on three types of substrates: 1) the lower stems of cordgrass plants,Spartina alterniflora, 2) detrital mats, and 3) exposed cordgrass roots along erosional scraps. Spawning behavior during egg deposition and fertilization was similar for all three substrates. Females released eggs during a rapid fluttering motion of the posterior half of the body. A similar movement accompanied release of sperm by males. Behavior of fish just prior to spawning insured deposition of gametes at locations that provided protection from thermal and drying stress during development. Eggs were deposited at mean intertidal elevations of 1.8 and 1.5 meters above mean low water (MLW) at respective study sites. They were exposed to the atmosphere for approximately ten hours between successive high tides.During spawning runs in which eggs were deposited at the base of cordgrass plants, ambient dissolved oxygen concentrations of the water in the spawning area were sometimes reduced to < 1.0 mg. 1^–1. Spent fish, apparently incurring an oxygen debt while spawning, formed a nonschooling aggregation offshore from the spawning zone.The recurrent use of specific spawning substrates for egg deposition resulted in an uneven distribution of spawning runs along the shoreline at each study site.Contribution No. 409 to the Gulf Breeze Environmental Research Laboratory. Contribution No. 377 to the Belle W. Baruch Institute for Marine Biology and Coastal Research.     

Effect of body length and temperature on the crawling speed of Protophormia terraenovae larvae (Robineau-Desvoidy) (Diptera Calliphoridae)

This work investigates variation in the crawling speed of Protophormia terraenovae larvae (Robineau-Desvoidy) (Diptera Calliphoridae) as a function of body length and ambient temperature. A video-tracking system was used to follow the movement of larvae in an experimental arena, and to estimate their average crawling speed. Recordings were carried out at various temperatures using larvae of different developmental stages. As temperature increased, the larvae crawled at a faster speed. Furthermore, speed increased as a function of body length. We present a general allometric relationship to express the average crawling speed of larvae as a combined function of temperature and body length, expressed in the following equation: speed (cm/min)=5.45 x log[length (mm)]+0.66 x temperature (degrees C)-12.8. These results are particularly useful in forensic entomology for estimating the time that elapsed following the larva's departure from the corpse. This information can provide more accuracy for post-mortem interval estimations and a better comprehension of larvae behaviour and displacement.     

Metabolic correlates of burst swimming capacity of juvenile and adult threespine stickleback (Gasterosteus aculeatus)

The relationship between burst swimming performance and muscle metabolic capacities was examined in juvenile and adult threespine sticklebacks (Gasterosteus aculeatus). The absolute burst speed measured during startle responses increased markedly with growth of juveniles, but this positive allometry did not continue in adults. The allometry of phosphofructokinase (PFK), lactate dehydrogenase, creatine phosphokinase activities and protein concentrations was positive in juveniles and became negative in adults. The lower activities in adults may reflect the mobilization of muscle proteins for reproduction. In juveniles, absolute burst swimming and muscle glycolytic capacity show a similar allometry. However, when the influence of factors such as size and age was removed by calculating residuals from multiple regressions, variation in muscle enzyme activities in juveniles did not explain variation in their swimming capacity. In adults, interindividual variation in PFK and cytochrome C oxidase activities was correlated with variation in the burst swimming capacity. Apparently, mobilization of muscle proteins in support of reproduction may lead muscle enzyme levels to limit burst performance. Accepted: 9 November 1998     

Larval biology of butterflyfishes (Pisces,Chaetodontidae): what do we really know?

Synopsis Relatively little is known of the pelagic portion of the life history of butterflyfishes. Eggs are small (<1 mm), pelagic and hatch in less than 30 hours. Most species pass through a so-called tholichthys larval interval characterized by elaborate, distinctive head spination:Coradion larvae have different head spination. While older chaetodontid larvae can be identified by adult characters, young (preflexion) larvae generally cannot now be identified below family. In tropical plankton studies chaetodontid larvae averaged <0.1% of larvae captured, and occurred in 13% of samples. This rarity is a major hindrance to further work, but is not unexpected in view of adult abundance. Larvae of a few taxa are most abundant in shelf waters, but larvae of many chaetodontid taxa seem to be most abundant in oceanic waters. In either case, waters near reefs have the fewest chaetodontid larvae. Offshore maxima of larvae appear to exist a few kilometers seaward of Great Barrier Reef ribbon reefs. Chaetodontid larvae may prefer the upper portion of the water column. Both size and age at settlement vary widely within the family and the large genusChaetodon, and the latter varies widely within species. Average size at settlement is less than 20 mm and age is less than 40 days. No correlation was found between size and age at settlement. Behaviour and feeding of chaetodontid larvae are essentially unstudied. Chaetodontid larvae seem to be least abundant in winter. The implications of these conclusions are discussed and some suggestions for further research are made. In all areas more work is needed.     

Characterization of the cDNAs Encoding Three GnRH Forms in the Pejerrey Fish <Emphasis Type="Italic">Odontesthes bonariensis</Emphasis> (Atheriniformes) and the Evolution of GnRH Precursors

Most vertebrates express two gonadotropin releasing hormone (GnRH) variants in brain tissue but there is an increasing number of fish species for which a third GnRH form has been detected. We characterized the precursors (cDNAs) of all three forms expressed in the brain of the pejerrey (silverside) fish, Odontesthes bonariensis (Atheriniformes): type I (GnRH-I; 440 bp), type II (GnRH-II; 529 bp), and type III (GnRH-III; 515 bp). The expression of these GnRHs precursors was also observed in peripheral tissues related to reproduction (gonads), visual and chemical senses (eye and olfactory epithelium), and osmoregulation (gill), suggesting that in teleost fish and possibly other vertebrates GnRH mediates directly or indirectly many other functions besides reproduction. We also present a comprehensive phylogenetic analysis including representatives of all chordate GnRH precursors characterized to date that supports the idea of two main paralogous GnRH lineages with different function. A “forebrain lineage” separates evolutionarily from the “midbrain lineage” as a result of an ancient duplication (ca. 600 million years ago). A third, fish-only clade of GnRH genes seems to have originated before the divergence of fish and tetrapods but retained only in fish. Phylogenetic analyses of GnRH precursors (DNA and protein sequences) under different optimality criteria converge on this result. Although alternative scenarios could not be statistically rejected in this study due to the relatively short size of the analyzed molecules, this hypothesis also receives support from chromosomal studies of synteny around the GnRH genes in vertebrates. [Reviewing Editor: Dr. Axel Meyer]     

Field and laboratory observations of spawning periodicity and behavior of a northern population of the Atlantic silverside,Menidia menidia (Pisces: Atherinidae)

Synopsis The spawning periodicity and mating behavior of a northern population of the Atlantic silverside, Menidia menidia, was studied both in the field (Salem Harbor, Massachusetts) and in laboratory experiments. Spawning in the field coincided with new and full moons. Under conditions of unlimited food availability in artificial outdoor pools that received natural celestial illumination or in indoor aquaria receiving no evening illumination, spawning occurred every 1–3 days rather than fortnightly. These results suggest that tidal influences are a primary factor that synchronizes spawning in M. menidia. Published reports of diel time of spawning in both marine and freshwater species of Menidia indicate a generic tendency to spawn during mid-morning. This pattern coupled with high tides that cover suitable spawning substrates during mid-morning only at fortnightly intervals could account for the semilunar spawning cycle in marine populations of Menidia. Although general characteristics of the reproductive ecology of M. menidia in Massachusetts were similar to a thoroughly studied population in South Carolina, several differences were evident. The breeding season was shorter in Massachusetts (late; April–June), and occurred over a much lower range of temperatures (9–21°C). Intensity and frequency of spawning was correlated with the height of high tide. Eggs were deposited only on mats of intertidal, filamentous algae rather than on roots or stems of Spartina alterniflora or other intertidal vegetation. Promiscuous spawning occurred in small, highly male-dominated groups of fish, primarily after the tide had begun to recede, and often at the water's edge. No predation on spawning adults was observed but the mummichog, Fundulus heteroclitus, fed daily on developing embryos during high tide. Contribution No. 81, Massachusetts Cooperative Fisheries Research Unit, Contribution No. 349, Marine Sciences Research Center, State University of New York at Stony Brook.     

Factors affecting calculation of nutritional induces for foliage-fed insects: an experimental approach

To determine how nutritional indices for insects fed leaves are affected by the experimental conditions and the physiology of the plant material, we used larvae of the buckmoth, Hemileuca lucina Hy. Ed. (Saturniidae) and their hostplant Spiraea latifolia Ait. Bork (Rosaceae). Under experimental conditions identical to those used to determine larval nutritional indices, we found that the age of leaves (new versus mature) significantly affected their metabolism and water loss, but simulated herbivory did not directly affect leaf metabolism. Over a 6-day test, nitrogen concentration showed an initial increase followed by a gradual decline, and was higher in new leaves compared to mature leaves. New leaves increased in protein concentration and then gradually returned to the initial level, whereas mature leaves changed little over the 6-day test. These changes in percent nitrogen and protein may largely reflect the disproportional changes in non-nitrogenous materials. Solitary and grouped larvae had similar growth rates on new leaves, but they differed on mature leaves. Deliberate manipulation of larvae during the course of an experiment significantly reduced relative growth rates by increasing duration of the stadium rather than by decreasing biomass gained. Two methods of estimating larval gut contents at mid-stadium were compared: weight of frass produced and weight of digestive tract and contents. After the end of the 4-day test period used to determine nutritional indices, the digestive tracts with food accounted for 10.8% of the larval dry weight. Larval frass produced in 24 h after the end of the test period comprised 9.3% of the larval dry weight. Correction factors for plant metabolism changed nutritional indices by 1 to 8%, while those for larval gut contents altered indices by 2 to 15%.     

Effects of size on Vervet (Cercopithecus aethiops) gait parameters: A cross-sectional approach

A comparison of the values of certain temporal and spatial locomotor parameters was made among ten different-aged (sized) vervet monkeys locomoting at nine identical speeds. Cycle and stance durations decreased across speed for all the animals; at any one speed both parameters also varied directly with body size. Stride length increased with speed for all the animals and was greater in the larger animals. Swing duration and hindlimb support length tended to be relatively consistent for each animal across speed, but varied among the animals directly with body size. Hindlimb duty factor decreased with speed for any one animal but showed no direct correlation with size. Hindlimb angular excursion also showed no correlation with size, nor did it show a simple relationship with speed. In terms of gaits and gait transitions, the data indicate that vervets use a very wide variety of gait types, which are not easily correlated with speed or body size. Furthermore, the data suggest the existence of a run–gallop transition zone of speeds for these animals, rather than the existence of a specific transition speed. Finally, the data were used to test intraspecifically the elastic and dynamic similarity models, both of which predict how locomotor parameters will change with size in animals. The results are generally consistent with the dynamic model.     

Fatty acid composition of wild Odontesthes bonariensis (Valenciennes 1835) larvae: implications on lipid metabolism and trophic relationships

The fatty acid composition of the pejerrey Odontesthes bonariensis larvae was studied to elucidate potential dietary relationships. Their principal fatty acids were characteristic for membrane lipids of aquatic organisms. The fatty acid composition varied little throughout seasons, with high proportions of 22 : 6(n‐3) (27% of total fatty acids), which is biosynthesized de novo from dietary precursor fatty acids and/or accumulated from the diet. Other major fatty acids were 16 : 0 and 18 : 0. The diatom‐typical 16 : 1(n‐7) and other dietary fatty acids (zooplankton and microplankton) are not reflected in the larvae, thus limiting the use of fatty acids as trophic markers for food web relationships of atherinopsids.