First estimates of metabolic rate in Atlantic bluefin tuna larvae

Atlantic bluefin tuna is an iconic scombrid species with a high commercial and ecological value. Despite their importance, many physiological aspects, especially during the larval stages, are still unknown. Metabolic rates are one of the understudied aspects in scombrid larvae, likely due to challenges associated to larval handling before and during respirometry trials. Gaining reliable estimates of metabolic rates is essential to understand how larvae balance their high growth needs and activity and other physiological functions, which can be very useful for fisheries ecology and aquaculture. This is the first study to (a) estimate the relationship between routine metabolic rate (RMR) and larval dry weight (DW) (mass scaling exponent) at a constant temperature of 26°C, (b) measure the RMR under light and darkness and (c) test whether the interindividual differences in the RMR are related to larval nutritional status (RNA/DNA and DNA/DW). The RMR scaled nearly isometrically with body size (b = 0.99, 0.60–31.56 mg DW) in contrast to the allometric relationship observed in most fish larvae (average b = 0.87). The results show no significant differences in larval RMR under light and darkness, suggesting similar larval activity levels in both conditions. The size explained most of the variability in RMR (97%), and nutritional condition was unrelated to the interindividual differences in routine metabolism. This is the first study to report the metabolic rates of Atlantic bluefin tuna larvae and discuss the challenges of performing bioenergetic studies with early life stages of scombrids.     

Susceptibility of three lepidopteran pests to five entomopathogenic nematodes and in vivo mass production of these nematodes

Abstract

An investigation was conducted in pots to access the susceptibility of three lepidopteran pests, namely, gram pod borer, Helicoverpa armigera, greater wax moth, Galleria mellonella, and rice moth, Corcyra cephalonica, to two recently described species, Steinernema masoodi, S. seemae, and three indigenous S. carpocapsae, S. glaseri and S. thermophilum entomopathogenic nematodes (EPN). The suitability of these lepidopterans for the in vivo mass production of the nematodes was also estimated. Among the five species of EPN, S. masoodi, S. seemae and S. carpocapsae were found most pathogenic to C. cephalonica, bringing about mortality within 24 h, followed by H. armigera (36, 38 and 48 h, respectively) and G. mellonella (30, 36 and 48 h, respectively). The other species of EPN, viz., S. glaseri and S. thermophilum was the least pathogenic, which killed the larvae of C. cephalonica in 29 and 36 h, respectively, G. mellonella in 48 h, and H. armigera in 38 and 56 h, respectively. Galleria mellonella was found the most suitable host for the mass production of infective juveniles (IJs) of S. seemae, which yielded higher IJs than S. carpocapsae. Helicoverpa armigera was the next best suitable alternate host, which produced maximum IJs in case of S. seemae followed by S. masoodi, S. carpocapsae, S. glaseri and S. thermophilum. Rice moth, Corcyra cephalonica was the least suitable host. The susceptibility of H. armigera to five tested EPN species and susceptibility of G. mellonella and C. cephalonica to S. masoodi and S. seemae are new records.     

Butterflies of the South Pacific

ABSTRACT

Larvae of the invasive mosquito Culex quinquefasciatus Say are morphologically similar to those of the native Culex pervigilans Bergroth, yet distinguishing these species can be hampered by morphological variations in Cx. quinquefasciatus. We present detail about the extent of these variations in an urban population of Cx. quinquefasciatus in Auckland. To aid in identification of this exotic species, we provide images of key diagnostic characters and some observed exceptions to these. Details regarding variation in diagnostic characters for < 3rd instar and 3rd/4th instar larvae are given. Of the nine characters used for identification, three were highly consistent (dorsal papillae, mantle plate, pecten teeth); each observed in > 90% of larvae, although these characters were not always visible. Other characters were less reliable, for instance, the expected position of seta 1a-S in relation to the pecten teeth was observed in < 10% of larvae. Further exploration of regional morphological variation in both Cx. quinquefasciatus and Cx. pervigilans is recommended, ideally with associated molecular characterisation.     

Larval biomass and chemical composition at hatching in two geographically isolated clades of the shrimp Macrobrachium amazonicum: intra- or interspecific variation?

The shrimp Macrobrachium amazonicum (Heller 1862) has an extremely large geographic range (>4000?km across) in northern and central South America, comprising estuarine and fully limnic inland populations, which are hydrologically isolated from each other. Significant variations in ecology, physiology, reproduction, and larval development suggest an at least incipient allopatric speciation due to limited genetic exchange. In a comparative experimental investigation with shrimps from the Pantanal (upper Paraguay River basin) and the Amazon delta, respectively, we measured larval body size, dry weight (W), biochemical (total protein; lipid; fatty acids, FA), and elemental composition (carbon, hydrogen, nitrogen; collectively CHN) at hatching. All these early larval traits are relevant for the degree of developmental dependence on planktonic food sources. Various consistent differences were observed between the two populations: Newly hatched larvae produced by shrimps from the Amazon delta were significantly smaller and showed lower values of W, CHN, protein, and unsaturated FA compared to those from the Pantanal. On the other hand, they contained significantly higher quantities of total lipid and saturated FA and, in consequence, higher ratios of lipid:protein, C:N, and saturated:unsaturated FA. All these differences in biomass and chemical composition suggest that the larvae of the Amazon population are energetically better adapted to planktonic food limitation, which likely occurs during riverine downstream transport toward coastal marine waters, also explaining previous observations of much stronger initial starvation tolerance in larvae from the Amazon versus those from the Pantanal. The latter develop in highly productive lentic inland waters, where large body size, an early onset of feeding, and a strong musculature (indicated by a high protein content) should facilitate their role as planktonic predators and allow for fast growth. An initial independence from food (lecithotrophy in the zoea I stage) as well as a preference for oligohaline rather than fully limnic conditions observed in the Pantanal larvae are interpreted as traits that have persisted from an ancestral coastal marine clade. Altogether, consistent ontogenetic differences between shrimps from the Pantanal and the Amazon estuary support the hypothesis that the taxon M. amazonicum comprises a complex of closely related but separate species.     

A study on the energy source in the developing embryo of the mangrove horseshoe crab,Carcinoscorpius rotundicauda (Latreille)

The mangrove horseshoe crab, Carcinoscorpius rotundicauda, is an Asian species found in Malaysia. This ancient arthropod has a long incubational period during which it depends on various energy sources for both embryogenesis and organogenesis. This study describes the trend of energy utilization from the endogenous reserves by the developing embryos from 0 to 40 days of incubation (until the hatching of the larvae). The dry weight, insoluble protein, carbohydrate, glycogen and lipid showed a declining trend from 0 to 40 days of incubation, whereas the wet weight, water content, ash content and soluble protein showed an increasing trend. Selected micro-elements such as Cu²⁺, Fe²⁺ and Zn²⁺ also demonstrated an interesting trend in the developing eggs when the egg mass was subjected to inductively coupled plasma mass spectrometry analysis, where these elements showed a high correlation with the moulting stages and egg development. Maximum variations within the micro-elements were observed during the 1st (10 days after fertilization) and 2nd (35–36 days after fertilization) moulting stages within the developing eggs. This study clearly indicated that the moulting cycles of C. rotundicauda during embryonic development influence energy utilization in the form of carbohydrates, lipids, proteins, glycogen and other micro-elements.     

The effect of salinity on larval survival and development in the sea urchin Echinometra lucunter

Summary

Reductions in salinity can have adverse effects on larval development and larval survival in some invertebrate taxa but not others. Salinity tolerance of larvae may be particularly important in echinoderms because they are both poor ion regulators and stenohaline. I examined the effect of six levels of salinity (15, 18, 21, 24, 27 and 33 PSU) on survival and rate of development of larvae in the subtropical sea urchin Echinometra lucunter. In the short-term, mortality rate was significantly lower in 33 PSU than in all other salinities except 27 PSU, and it was significantly greater in 15 and 18 PSU than in all higher salinities. In the long-term, daily and cumulative mortality were significantly greater in 15 PSU than in most other salinities over 11 days of development (except for cumulative mortality in 18 PSU). They were significantly greater in 18 PSU than in 21 PSU or 33 PSU over a period of 13 days. Furthermore, daily mortality was significantly greater in 18 PSU than in 24 PSU or 27 PSU at 13 d after fertilization. Daily and cumulative mortality were significantly lower in 33 PSU than in 21, 24 or 27 PSU over a period of 17 days. Although in the control (33 PSU) 75% of larvae completed development to the 8-arm stage at 35 d, no larvae developed further than the 4-arm stage in 18, 21, 24 or 27 PSU; in 15 PSU, ~60% of larvae did not develop further than swimming blastulae. Since prolonged exposure to salinities as high as 27 PSU (frequently recorded in the adult habitat) can result in great larval losses, adaptive behaviours that prevent larvae from entering water layers of low salinity will enhance their chance for survival.     

Mini review: Hydrodynamics of larval settlement into fouling communities

Abstract

Flowing water delivers planktonic larvae to surfaces, but also dislodges them. This paper reviews experiments in the field and in laboratory flumes, as well as mathematical models, which have revealed how the interaction of ambient water motion with a developing fouling community affects larval settlement. Although mean current velocities across fouling communities in harbours are low, instantaneous velocities can be much higher due to turbulence and to the velocity oscillations of wind chop and ship wakes. As a fouling community develops, its topography becomes more complex and the range of flow microhabitats on the spatial scale of larvae increases. In spite of the prevalence of waves in shallow coastal habitats, and in spite of the importance to settlement of the fine-scale instantaneous velocities encountered by larvae, most studies of flow effects on larval settlement have focused on unidirectional currents and on temporally- and spatially-averaged aspects of the flow.     

Oxygen-depleted surfaces: a new antifouling technology

A novel, non-toxic strategy to combat marine biofouling is presented. The technology is paint with additions of up to 43% of industrial protein. Through microbial degradation of the protein component, an oxygen-depleted layer rapidly forms in a 0.2 mm layer close to the paint surface. With the present paint formulations, a stable, O₂-depleted layer can persist for 16 weeks. Barnacle larvae (cyprids) did not settle on panels where oxygen saturation was <20%, and cyprids were killed when exposed to O₂-free water for more than 1 h. It is also shown that the O₂-depleted layer will rapidly reform (within 15 min) after exposure to turbulent flow. Field exposure of panels for 16 weeks showed that paint with protein reduced fouling by barnacles and bryozoans by 80% and close to 100%, respectively. The results suggest that this novel technology may be developed into a non-toxic alternative to copper-based antifouling paints, especially for pleasure boats in sensitive environments. There is clearly potential for further development of the paint formulation, and a full-scale test on a boat-hull suggested that service-life under realistic operations needs to be improved.     

食品级惰性粉对三种储藏物害虫生长发育的影响

应用粉剂药膜法,一种食品级惰性粉——4号粉相应剂量处理赤拟谷盗Tribolium castaneum(Herbst)、烟草甲Lasioderma serricorne(Fabricius)、锯谷盗Oryzaephilus surinamensis(Linnaeus)的卵和1龄幼虫,赤拟谷盗、锯谷盗、烟草甲的卵平均孵化率均在97%以上,处理后卵孵化的1龄幼虫平均死亡率均在96%以上;处理3种害虫的1龄幼虫其平均死亡率均在99%以上。结果表明食品级惰性粉对3种试虫卵的孵化率几乎没有影响,但对其1龄幼虫有较好的防治效果。通过混粮法应用正交试验研究发现,惰性粉剂量和小麦含水量对赤拟谷盗F1代防治效果均有显著影响。当小麦处于安全水分时(含水量12%¹4%),10014%),100¹50 mg/kg 4号粉能有效防治赤拟谷盗F1代。