Experimental studies on the larval development of the shrimpsCrangon crangon andC. allmanni

Larvae of the shrimpsCrangon crangon L. andC. allmanni Kinahan were reared in the laboratory from hatching through metamorphosis. Effects of rearing methods (larval density, application of streptomycin, food) and of salinity on larval development were tested only inC. crangon, influence of temperature was studied in both species. Best results were obtained when larvae were reared individually, with a mixture ofArtemia sp. and the rotiferBrachionus plicatilis as food. Streptomycin had partly negative effects and was thus not adopted for standard rearing techniques. All factors tested in this study influenced not only the rates of larval survival and moulting, but also morphogenesis. In both species, in particular inC. crangon, a high degree of variability in larval morphology and in developmental pathways was observed. Unsuitable conditions, e.g. crowding in mass culture, application of antibiotics, unsuitable food (rotifers, phytoplankton), extreme temperatures and salinities, tend to increase the number of larval instars and of morphological forms. The frequency of moulting is controlled mainly by temperature. Regression equations describing the relations between the durations of larval instars and temperature are given for bothCrangon species. The number of moults is a linear function of larval age and a power function of temperature. There is high variation in growth (measured as carapace length), moulting frequency, morphogenesis, and survival among hatches originating from different females. The interrelations between these different measures of larval development in shrimps and prawns are discussed.     

Veligers from the nudibranch <Emphasis Type="Italic">Dendronotus</Emphasis><Emphasis Type="Italic">frondosus</Emphasis> show shell growth and extended planktonic period in laboratory culture

The planktonic period of planktotrophic veliger larvae from the nudibranch Dendronotus frondosus was characterized by laboratory culture methods. Larvae in culture successfully metamorphosed at 73–86 days after hatching. These veligers have Type 2 (Thompson) larval shells that significantly increased in length over the first 7–14 days after hatching. Direct observations of the development of nudibranch larvae with Type 2 protoconchs are limited, and these data help clarify previous attempts to correlate shell type and growth with minimum planktonic periods. Although these are not absolute values for the planktonic period of D. frondosus larvae, these data show the potential for extended larval dispersal and may help explain reports of an extensive geographic range in north-temperate waters for this species.     

Diapause hormone directly stimulates the prothoracic glands of diapause larvae under juvenile hormone regulation in the bamboo borer,Omphisa fuscidentalis Hampson

Larval diapause in many lepidopteran insects is induced and maintained by high juvenile hormone (JH). In the case of the bamboo borer, Omphisa fuscidentalis, the effect of JH is the opposite: The application of juvenile hormone analog (JHA: S‐methoprene) terminates larval diapause, unlike in other insect species. Here, we analyzed the expression of JH‐receptor Met, DH‐PBAN, and Kr‐h1 in the subesophageal ganglion (SG) from October to April using semi‐quantitative polymerase chain reaction (PCR). The results show that OfMet and OfDH‐PBAN messenger RNA in the SG are mainly expressed during the larval diapause stage, while OfKr‐h1 increases during the pupal stage. Using tissue culture techniques and an enzyme‐linked immunosorbent assay (ELISA), diapause hormone (DH) was found to induce ecdysteroidogenesis in the culture medium of the prothoracic gland (PG) after incubation for 30 min with 25 ng and 50 ng of DH. Thus, DH is a novel stimulator for the PG. We identified a DHR homolog in the bamboo borer and confirmed that it is expressed in the PG. In addition, for in vitro experiments, DH increased the expression levels of OfDHR, OfEcR‐A, and ecdysone‐inducible genes in the PG. These results demonstrate that DH can function as a prothoracicotropic factor, and this function of DH might be through of DHR expressed on PG cells. Consequently, DH is one of the key factors in larval diapause break which is triggered by JH in the bamboo borer, O. fuscidentalis.     

Isolation,characterization, and in vitro culture of larval and adult epidermal cells of the frogXenopus laevis

Summary Methods for the isolation and in vitro culture of larval and adultXenopus laevis epidermal cells have been developed. Epidermal cells of stage 52–54 tadpoles and adult epidermal cells were enzymatically dissociated and purified (98%) by Percoll-density centrifugation and unit-gravity sedimentation. Both cell types attached on fibronectin-coated dishes and proliferated for 1 wk when the proper medium was used. There were four significant differences between larval and adult cells: a) Adult cells had a greater buoyant density than larval cells. b) Keratin synthesis patterns were markedly different. c) A combination of medium F12 and Eagle's minimum essential medium was optimal for growth of larval cells whereas MCDB151 medium was optimal for adult cells. d) Adult cells needed fetal bovine serum (>5%) whereas larval cells grew without fetal bovine serum. In contrast to these differences, larval and adult cells had two similar properties: a) Insulin had a potent effect on the growth of both cells, and b) The optimal Ca⁺⁺ concentration for cell growth was quite low for both cell types; 0,1 mM for larval cells and below 0.05 mM for adult cells. These results suggest that low Ca⁺⁺ levels are essential for both cornifying (adult) and uncornifying (larval) amphibian keratinocytes. The culture techniques described herein for larval and adult epidermal cells provide a new in vitro model for analyzing development of the epidermis during amphibian metamorphosis. This study was supported by grant (HD 24438) from the National Institutes of Health, Bethesda, MD.     

Failure of the introduction ofActinote anteas (Lep.: Acraeidae) from Costa Rica as a biological control candidate forChromolaena odorata (Asteraceae) in South Africa

Actinote anteas from Costa Rica was screened as a biological control candidate forChromolaena odorata in South Africa. Preliminary starvation trials suggest thatA. anteas is species specific. There are seven larval instars and the life cycle is completed in 101–169 days. The culture died out after three generations possibly because of incompatibility with the form of the local species ofC. odorata or disease.     

Oviposition,larval preference,and larval performance in two polyphagous species: does the larva know best?

It is expected that females preferentially oviposit on plant hosts that allow for optimal larval performance. However, this expectation contradicts empirical evidence where adults do not always choose the best host for their descendants. Recent evidence suggests that females’ host selection depends on the number of potential hosts. Females from oligophagous species seem to be able to choose an appropriate host in terms of larval performance, whereas in polyphagous species, adult oviposition preference is not related with larval performance. This suggests that larvae in polyphagous species could be taking a more active role in host selection than their mothers. Here, we evaluated the oviposition preference and the larval preference and performance of two polyphagous species of economic importance, Copitarsia decolora (Guenée) (Lepidoptera: Noctuidae: Cuculliinae) and Peridroma saucia (Hübner) (Lepidoptera: Noctuidae: Noctuinae), on eight species of cultivated plants. In laboratory and greenhouse choice assays, we tested adult preference for oviposition and larval preference at 1 and 24 h. Larval performance was measured in terms of survival to adulthood, length of larval period, and pupal weight. We found that both adult females and larvae actively choose their hosts and that the larval preference toward the hosts is related to the females’ preference in both herbivore species. However, the females and larvae did not preferentially select the host with the best larval performance, indicating that larval performance is not related to female or larval preference and that other selective pressures are influencing the choice of the host plant in these two species.     

Observations on development,larval growth and metamorphosis of four species of aplysiidae (gastropoda: Opisthobranchia) in laboratory culture

The development of simple, reliable techniques for the laboratory culture of aplysiid gastropods through their complete life cycle, has enabled us to study the larval biology, metamorphosis, and early juvenile development of these animals. Egg masses, duration of the embryonic phase, veligers, and larval growth and development are described for four species of Hawaiian Aplysiidae, namely, Aplysia dactylomela Rang, Aplysia Juliana Quoy and Gaimard, Dolabella auricularia (Lightfoot) and Stylocheilus longicauda (Quoy and Gaimard). Metamorphosis and early juvenile development of A. Juliana are described in detail with additional comments on these processes in the other three species. Length of the embryonic phase and size of the veliger at hatching are a function of the size of the uncleaved egg. All four species develop planktotrophically and have ≈ 30-day larval phases. In each species the larval phase includes a period of rapid shell growth to a species-specific size followed by a non-growth period during which other morphological developments occur to culminate in metamorphic competence. The larvae of each species metamorphose preferentially on a particular species of benthic algae. The events of metamorphosis require 2 to 4 days for completion and transform the planktonic filter-feeding larva into a benthic, radular-feeding juvenile. Postlarval development includes growth of the shell, parapodia, oral tentacles, rhinophores, anal siphon, and structures of the mantle cavity.     

Some aspects of biology and aquaculture potentials of <Emphasis Type="Italic">Tilapia guineensis</Emphasis> (dumeril) in Nigeria

The paper emphasizes on the several attempts made to raise the brackish water tilapia species, Tilapia guineensis both on an experimental and production basis by researchers and fish farmers in Nigeria. Besides, the aquaculture potentials of Tilapia guineensis have been reported by several authors. However, problems exist which are not found with the culture of other tilapia species. Even under most favourable conditions (e.g. the monosex culture of Tilapia guineensis), a poor growth rate and a mediocre feed conversion do not presage profitable aquaculture exploitation. The present review therefore throws light on areas of further research to enhance the growth performance of Tilapia guineensis with emphasis on fish larvae nutrition and first feeding (development of bio-encapsulated feed for larval fish based on nutritionally enriched nematodes and Calanoid copepods), digestibibilty of the feed ingredients, elucidation of the dietary protein requirements, improved culture technique through the use of the Recirculating Aquaculture Systems and the adoption of the most recent technology (The YY Male technology) that produces Genetically Male Tilapia through genetic manipulation. Specific recommended areas for further research are also proffered.     

Determining the optimum temperature and salinity for larval culture,and describing a culture protocol for the conservation aquaculture for European smelt Osmerus eperlanus (L.)

Populations of anadromous European smelt Osmerus eperlanus (L.) are declining across its geographical range in northern Europe, but no practical culture techniques exist to develop stock enhancement programmes for this species. In this study, a culture protocol is described to rear fish from fertilised eggs to mature adults in 2 years involving the use of ‘green water’, live feed and artificial diets. The sequence of embryonic development for eggs incubated at 10°C/0 ppt was described and photographed. To determine the optimum conditions for larval culture, fertilised eggs were reared at a range of salinities (0–20 ppt) and temperatures (5–18°C) until first feeding. Best hatching success (ca. 97%), size at hatch (ca. 0.8 mm) and survival to first feeding (ca. 96%) of larvae were achieved under combined conditions of low salinity (0–0 ppt) and temperature (5–10°C). No larvae survived a salinity of 20 ppt. The time taken from fertilisation to hatch (FtH) and hatching duration (HD) were temperature-dependent ranging from 42 days FtH and 10 days HD at 5ºC, to 10 days FtH and 2 days HD at 18°C irrespective of salinity. The results indicate that conservation programmes could utilise existing salmonid hatchery facilities (i.e. freshwater, ≤10°C water temperature) for stock enhancement. Since on-growing of smelt involves the logistical and technical problems of live feed production, it is recommended that smelt enhancement programme utilise freshwater hatchery facilities to rear fish until hatching, and then stock out onto known spawning grounds in rivers allowing hatched larvae to drift into estuaries to complete the larval and juvenile phases. This approach would minimise the time spent in the hatchery post-hatching, eliminate the need for live food production, prevent the development of predator-naïve fish, and hence would mimic the natural life cycle of the species as closely as possible.     

All in the ears: unlocking the early life history biology and spatial ecology of fishes

Obtaining biological and spatial information of the early life history (ELH) phases of fishes has been problematic, such that larval and juvenile phases are often referred to as the ‘black box’ of fish population biology and ecology. However, a potent source of life‐history data has been mined from the earstones (otoliths) of bony fishes. We systematically reviewed 476 empirical papers published between 2005 and 2012 (inclusive) that used otoliths to examine fish ELH phases, which has been an area of increasing attention over this period. We found that otolith‐based research during this period could be split into two broad themes according to whether studies examined: (i) biological objectives related to intrinsic processes such as larval and juvenile age, growth and mortality, and/or (ii) spatial objectives, such as habitat use, dispersal and migration. Surprisingly, just 24 studies (5%) explored a combined biological–spatial objective by simultaneously exploiting biological and spatial information from otoliths, suggesting much more scope for such integrated research objectives to be answered via the use of multiple otolith‐based techniques in a single study. Mapping otolith analytical techniques across these two approaches revealed that otolith structural analysis was mainly used to investigate biological processes, while otolith chemical analyses were most often applied to spatial questions. Heavy skew in research effort was apparent across biomes, with most (62%) publications specific to marine species, despite comparable levels of species richness and the importance of freshwater taxa (just 15% of papers). Indeed, around 1% (380 species) of a possible 31400+ extant species were examined in our surveyed papers, with a strong emphasis on temperate marine species of commercial value. Potential model species for otolith‐based ELH ecology research are arising, with the eel genus Anguilla (24 studies) and the European anchovy Engraulis encrasicolis (14 studies) attracting more research effort than most other taxa. While there is a preponderance of common techniques (e.g. daily otolith increment counts, increment widths), novel techniques such as transgenerational marking and computed X‐ray tomography, are increasingly being applied in published studies. The application of an integrative approach based on a combination of emerging techniques and traditional methods holds promise for major advances in our understanding of ELH fish ecology and to shine light into the ‘black box’ of fish ecology.     

Ontogenetic changes in responses to settlement cues by Anemonefish

Population connectivity for most marine species is dictated by dispersal during the pelagic larval stage. Although reef fish larvae are known to display behavioral adaptations that influence settlement site selection, little is known about the development of behavioral preferences throughout the larval phase. Whether larvae are attracted to the same sensory cues throughout their larval phase, or exhibit distinct ontogenetic shifts in sensory preference is unknown. Here, we demonstrate an ontogenetic shift in olfactory cue preferences for two species of anemonefish, a process that could aid in understanding both patterns of dispersal and settlement. Aquarium-bred na?ve Amphiprion percula and A. melanopus larvae were tested for olfactory preference of relevant reef-associated chemical cues throughout the 11-day pelagic larval stage. Age posthatching had a significant effect on the preference for olfactory cues from host anemones and live corals for both species. Preferences of olfactory cues from tropical plants of A. percula, increased by approximately ninefold between hatching and settlement, with A. percula larvae showing a fivefold increase in preference for the olfactory cue produced by the grass species. Larval age had no effect on the olfactory preference for untreated seawater over the swamp-based tree Melaleuca nervosa, which was always avoided compared with blank seawater. These results indicate that reef fish larvae are capable of utilizing olfactory cues early in the larval stage and may be predisposed to disperse away from reefs, with innate olfactory preferences drawing newly hatched larvae into the pelagic environment. Toward the end of the larval phase, larvae become attracted to the olfactory cues of appropriate habitats, which may assist them in identification of and navigation toward suitable settlement sites.     

Detecting host–parasitoid interactions in an invasive Lepidopteran using nested tagging DNA metabarcoding

Determining the host–parasitoid interactions and parasitism rates for invasive species entering novel environments is an important first step in assessing potential routes for biocontrol and integrated pest management. Conventional insect rearing techniques followed by taxonomic identification are widely used to obtain such data, but this can be time‐consuming and prone to biases. Here, we present a next‐generation sequencing approach for use in ecological studies which allows for individual‐level metadata tracking of large numbers of invertebrate samples through the use of hierarchically organised molecular identification tags. We demonstrate its utility using a sample data set examining both species identity and levels of parasitism in late larval stages of the oak processionary moth (Thaumetopoea processionea—Linn. 1758), an invasive species recently established in the United Kingdom. Overall, we find that there are two main species exploiting the late larval stages of oak processionary moth in the United Kingdom with the main parasitoid (Carcelia iliaca—Ratzeburg, 1840) parasitising 45.7% of caterpillars, while a rare secondary parasitoid (Compsilura concinnata—Meigen, 1824) was also detected in 0.4% of caterpillars. Using this approach on all life stages of the oak processionary moth may demonstrate additional parasitoid diversity. We discuss the wider potential of nested tagging DNA metabarcoding for constructing large, highly resolved species interaction networks.     

Mysids in toxicity testing — a review

The use of mysid shrimp, particularly the genusMysidopsis, along with specific testing procedures, has become accepted in aquatic toxicology. Investigators have developed methodologies for both culture and testing of these organisms. Acute and chronic (life cycle) toxicity tests in addition to dredge spoil and effluent tests with mysids are now becoming common. Attempts have been made to use mysids as test organisms in behavioral, physiological, nutritional, and food-chain studies. In general,Mysidopsis spp. have been shown to be as sensitive or more sensitive to toxic substances than other marine species tested. The ease of handling and culture, relative sensitivity to toxicants, short life cycle, small size and direct larval development make these organisms desirable for research purposes. Continued research using mysid species will probably demonstrate even greater usefulness of these organisms in assessment of pollutant impacts on estuarine or marine communities.     

Allocation of reproductive effort in female Arrenurus spp. water mites (Acari: Hydrachnidia; Arrenuridae)

Summary Twenty-seven species of water mites of the genus Arrenurus were compared with respect to allocation of reproductive effort. Clutch volume was positively correlated to female volume, female volume was positively correlated with clutch size and with larval volume, while clutch size and larval volume were negatively correlated. In threespace, corresponding to female volume, clutch size and larval volume, species were arranged along two trajectories representing separate reproductive strategies. The strategy characterized by small larvae, large clutches and large females corresponded to species of the subgenus Arrenurus, known to be larval parasites of adult Odonata. Members of three subgenera, known to be larval parasites of adult Diptera, followed the second strategy of small clutch size and alrge larvae. Of nine species of mites tested for intraspecific relationships, only one significant relationship was found, between female volume and clutch size for A. (Megaluracarus) bartonensis.     

Population dynamics and resource utilization by larval Chironomidae (Diptera) in a backwater area of the River Danube

1. The five most abundant species of the larval chironomid community in a backwater area of the River Danube were analysed in terms of population dynamics and utilization of space from July 1985 to July 1986. The life histories of Prodiamcsa olivacea (Meigen), Cryptochironomus defectus (Kieffer), Harnischia curtilamellata (Malloch), Polypedilum laetum (Meigen) and Polypedilum scalaenum Schrank were described; the number of estimated generations per year was two for P. olivacea, H. curtilamellata, P. laetum and P. scalaenum and three for C. defectus. A decline in larval densities of P. olivacea and P. scalaenum was significantly correlated with increasing cumulative water discharge in an area close to a dam (P<0.01). 2. Spatial overlap and resource width were estimated for these chironomid species across four ranges of water depth, in three sections of the River Danube. An increasing mean spatial overlap between larval species coincided significantly with higher mean resource utilization in all cross-sections during the sampling period. Simulations of spatial overlap between randomized species associations were conducted for analyses of coexistence and dispersion between larval populations. On the basis of comparison with a neutral model, in which patches of individuals were randomly reassigned to habitat units, spatial segregation was significantly (P<0.05) different from chance for seventy-three out of 263 species pairs examined through the year. 3. An analysis of the spatial dispersion of each chironomid species (using the standardized Morisita index) suggested temporally and spatially varying patterns of dispersion, whereas the mean spatial segregation between patches of larval species might have resulted from temporary formations of random patches in this backwater area of the River Danube. 4. Spatial stability estimated as the minimum positive eigenvalue of the species matrix was significantly positively related to mean spatial segregation, indicating that a lower habitat segregation between patches of larval species pairs may lead to a destabilization of the larval species assemblage.     

A review on the biology and potential aquaculture of Dentex dentex

A very limited number of scientific studieshave been conducted on Dentex dentex inits natural environment yet, over the lastdecade, this species has been extensivelystudied in captivity. This sparid fish, highlyregarded in many countries of the Mediterraneancoasts, has recently been successfullyproduced, on a trial basis, in Greece, Italyand Spain, and may become a serious candidatefor aquaculture. Although the species was firstconsidered as protandric, later studies havecharacterized Dentex dentex as agonochoric species with bisexual juvenilephases. In recent times, it has become possibleto control and lengthen the spawning period forthe purpose of improving production management.Embryonic and larval development has beenextensively described, and the assaying of anumber of culture conditions and feedingprotocols have permitted us to overcome thedifferent stages of larval development.Survival rates, however, are still low and thefeeding requirements at each stage, especiallyduring the weaning period, are not clearlydefined. Nevertheless, growth rate, both atlarval and fattening stages, is high whencompared to that of gilthead sea bream (Sparus aurata).In spite of the many studiesperformed over recent years, the lack of a dryfeed precludes exploration of the full growthpotential of Dentex dentex under cultureconditions. During the larval and juvenileperiods, Dentex dentex exhibitsaggressive behaviour and high sensitivityto stress, and is prone to high mortality ratesdue to a number of pathological processes(systemic granuloma, epitheliocystis,vibriosis, etc.)