Effects of size and light on respiration and activity of walleye pollock (Theragra chalcogramma) larvae

The respiration rate and swimming activity of walleye pollock (Theragra chalcogramma) larvae were measured in the laboratory to determine how these were affected by body size (measured as dry weight), and amount of light. Size influenced respiration rates, but not activity. Activity increased with increased light, and as walleye pollock larvae developed, light had an increasingly important effect on respiration rate. For older larvae, light is an important factor affecting respiration rate and this may be due to an increased sensitivity to light. Thus, in addition to size, light plays an important role in the energetics of walleye pollock larvae.     

Red porgy (Pagrus pagrus) larval feeding performance and behavior at the onset of exogenous feeding

The feeding performance and behavior at the onset of exogenous feeding, 3 to 4 days after hatching (DAH), were studied in red porgy Pagrus pagrus larvae. Similar feeding efficiency and intensity were achieved for two feeding treatments (live or freeze-dried rotifers) suggesting that prey movement is not decisive for their detection and capture and demonstrating that at first feeding red porgy larvae can ingest inert food. Larvae feeding performance was not affected by a diet shift between treatments. Based on maximum rotifers consumption and gut evacuation time at 18 °C, the daily ration was estimated as 14.035 μg, considering 14 h of feeding and a 25% egg:female rotifer ratio. Larval swimming activity measured by video recording showed a close association with gut fullness and similar swimming patterns for 3 and 4 DAH larvae. However, 20.3% larger mouth gape and 54.6% higher swimming speed of the older larvae should provide a better feeding performance and more energy needed for growth.     

Size-dependent flight initiation by a lotic mayfly in response to a predatory fish

1. Laboratory experiments were performed to determine whether flight initiation by lotic mayfly larvae of Baetis tricaudatus exposed to the longnose dace ( Rhinichthys cataractae ) is affected by an individual's size and its physiological state.
2. We used a three factorial ANOVA design to test whether flight initiation distances (FIDs) were affected by Baetis size (small, large), starvation level (low, high), and the length of a predator-free foraging period (short, long).
3. FIDs were significantly affected by the interaction between Baetis size and starvation level, and the main level effects of starvation and Baetis size. FIDs of small larvae were unaffected by starvation level and the length of the predator-free feeding period, whereas starvation reduced FIDs of large larvae 2-fold.
4. Subsequent experiments showed that size-dependent differences in FIDs could not be attributed to size-specific differences in the economics of rates of food intake or gut evacuation. For both small and large larvae, food intake rates declined with increasing time spent foraging and both small and large larvae consumed the majority (70–75%) of food within the first 3 h of the 12-h feeding period. Similarly, gut evacuation declined with increasing starvation time and rates of evacuation did not differ between small and large larvae. These data suggest that size-dependent differences in flight initiation by Baetis larvae do not involve the energetics of food intake or processing.     

Size-dependent flight initiation by a lotic mayfly in response to a predatory fish

1. Laboratory experiments were performed to determine whether flight initiation by lotic mayfly larvae of Baetis tricaudatus exposed to the longnose dace ( Rhinichthys cataractae ) is affected by an individual's size and its physiological state.
2. We used a three factorial ANOVA design to test whether flight initiation distances (FIDs) were affected by Baetis size (small, large), starvation level (low, high), and the length of a predator-free foraging period (short, long).
3. FIDs were significantly affected by the interaction between Baetis size and starvation level, and the main level effects of starvation and Baetis size. FIDs of small larvae were unaffected by starvation level and the length of the predator-free feeding period, whereas starvation reduced FIDs of large larvae 2-fold.
4. Subsequent experiments showed that size-dependent differences in FIDs could not be attributed to size-specific differences in the economics of rates of food intake or gut evacuation. For both small and large larvae, food intake rates declined with increasing time spent foraging and both small and large larvae consumed the majority (70–75%) of food within the first 3 h of the 12-h feeding period. Similarly, gut evacuation declined with increasing starvation time and rates of evacuation did not differ between small and large larvae. These data suggest that size-dependent differences in flight initiation by Baetis larvae do not involve the energetics of food intake or processing.     

Gut evacuation of walleye pollock larvae in response to feeding conditions

Gut residence times of first-feeding walleye pollock larvae were measured at 6°C in continuous and discontinuous feeding regimes. Larvae fed tagged copepod prey evacuated their guts more quickly in continuous feeding as compared to the discontinuous feeding treatment. The mean gut residence time was estimated to be 5.0 h for larvae feeding continuously. Gut evacuation by larvae fed tagged prey and then isolated without food (discontinuous treatment) was slower and more variable, with an estimated gut residence time exceeding 8.0 h. Field and laboratory observations suggest that the larval fish gut may be modeled as an intermittent plug-flow reactor (PFR) in response to diel feeding patterns. The cyclical nature of gut dynamics has implications for gut content analyses and the estimation of daily food rations.     

Food consumption of vendace Coregonus albula larvae in Lake Lentua, Finland

The daily ration of vendace larvae (mean TL 10·1–12·8 mm) was assessed after a time-intensive field survey in Lake Lentua. Ten larvae were sampled every 2 h throughout the 10-day sampling period and their alimentary tract contents analysed. The gut was cut into four quarters of equal length and each quarter was analysed separately. This procedure enabled the assessment of the proportions of different zooplankton taxa in the diet based on the least degraded first-quarter contents and to reconstruct the entire gut contents. Secondly, the gut passage time of ingested zooplankton was evaluated by comparing the degradation rate of zooplankton in the guts of experimentally fasted larvae to the degradation of zooplankton in the gradient from pharynx to anus among the larvae sampled from the lake. Finally, food consumption was calculated as zooplankton individuals and carbon biomass based on the two variables, gut passage time of constantly feeding larvae and reconstructed gut contents. The daily ration of vendace larvae varied between 14 and 450 zooplankters in the monitored period.     

Comparative larval energetics of an ophiuroid and an echinoid echinoderm

The morphologically convergent larvae of the echinoderm classes Ophiuroidea and Echinoidea have been suggested to be functionally dissimilar when it comes to their capacities to feed, but little is known about whether these larvae are similar in terms of energetics. Here, we compare the energetics of early development of a tropical ophiuroid, Ophiocoma alexandri, and a temperate to tropical echinoid, Arbacia punctulata, two species with similarly sized eggs. Measurements of respiration and constituent analyses were performed on eggs and unfed larvae of both species. Members of both species showed an increase in oxygen consumption during morphogenesis followed by a lower, static rate once morphogenesis was complete (3 d for O. alexandri and 1.3 d for A. punctulata). Compared to the echinoid larvae, the ophiuroid larvae developed more slowly and had peak respiration rates that were 3.1× lower. Eggs of O. alexandri contained significantly more protein and significantly less triacylglycerol than eggs of A. punctulata. Energy utilization, as calculated via respiration measurements, closely matched decreases in energy content from the eggs to larvae as measured with biochemical constituent assays. Larvae of A. punctulata used 1.4× more energy to reach the pluteus stage than larvae of O. alexandri, and used 4× more energy during the first 9 d of larval life. These data suggest that echinoid larvae require more energy to develop to the feeding stage than ophiuroid larvae, and likewise have higher requirements for maintenance metabolism. Ophiuroid larvae may be more tolerant of low food levels due to their very low metabolic rates, but this advantage may be offset by their slower rate of development.     

Does excess dietary carbon affect respiration of <Emphasis Type="Italic">Daphnia</Emphasis>?

Like many invertebrate herbivores, Daphnia frequently face diets with excess carbon (C) relative to elements like phosphorus (P), and with limited ability to store C-rich compounds. To cope with this relative surplus of C they may either regulate the net uptake of C or dispose of excess assimilated C via increased release of dissolved organic carbon or CO₂. Here we investigate whether juvenile Daphnia magna use respiration as a means of stoichiometrically regulating excess C. Growth rate and respiration were measured under different algal food qualities (P-replete and P-depleted algae). Growth rate was strongly reduced by P-depleted food, implying a stoichiometric disposal of excess ingested C. Respiration rates of feeding animals were measured after short- (0.5 h), medium- (12 h) and long- (five days) term acclimation to P-limited food. The respiration rates of animals during active feeding were not affected by the acclimation period per se, whereas food quality had a significant effect; respiration rates of feeding animals increased slightly in individuals receiving low-P food under all acclimation regimes. Respiration was also measured on nonfeeding and fasting animals that had been acclimated for five days to P-limited food. Respiration rates of these animals were strongly affected by feeding conditions but not by food quality; feeding individuals had higher respiration rates than those deprived of food, which again had higher respiration than fasting animals. Although animals grown on low-P food had strongly reduced growth and thus were expected to have decreased respiration rates due to reduced growth-related costs, this seems to be canceled out by increased stoichiometric respiration under P-deficiency. These results indicate that D. magna partly releases excess C as CO₂, but other means of stoichiometric regulation most likely add to this.     

Effect of delayed first feeding on development and feeding ability of Paralabrax maculatofasciatus larvae

The impact of delayed feeding early in development on late feeding ability and development of spotted sand bass Paralabrax maculatofasciatus larvae was examined. Larvae were sampled from hatching until day 19 after delayed feeding for zero (control), 1, 2, or 3 days. Feeding incidence was evaluated as the percentage of larvae with food in the gut and feeding intensity was measured by direct counting of prey after dissection of the gut. Delayed feeding effects due to starvation were observed early in development. By day 5, significant differences ( P  < 0·05) were observed between controls and larvae submitted to degrees of delayed feeding, including total length ( L _T), eye diameter, and the size of the head, liver, gut, muscles and body. Differences were still apparent in L _T, and body, liver and muscle heights at the end of the studied period. Larvae under total starvation did not survive beyond day 5. Initial feeding incidence was 35, 60, 90 and 10% for larvae first fed on day 2, 3, 4 or 5, respectively. Mean ±  s . d . feeding intensity was 3·6 ± 0·8, 2·8 ± 1·3, 5·2 ± 0·3, and 10·2 ± 1·5 rotifers per larva depending on whether larvae were initially fed on day 2, 3, 4 or 5, respectively. The point of no return occurred between 4 and 5 days after hatching.     

Effect of Early Introduction of Microencapsulated Diet to Larval Atlantic Halibut, Hippoglossus hippoglossus L. Assessed by Microarray Analysis

An experimental microdiet prepared using an internal gelation method was used to partially replace the traditional live feed (Artemia) for larval Atlantic halibut, Hippoglossus hippoglossus L. Three trials were conducted with microdiet introduced at 20, 32, and 43 days post first feeding and larvae were sampled at approximately 2, 13, 23, and 33 days after microdiet introduction in each trial. The success of feeding was assessed by morphometrics and histological analysis of gut contents. Microdiet particles were readily consumed after a period of adaptation and provided an adequate source of nutrients with no significant increase in mortality in the microdiet-fed group compared to the control group. However, growth was limited and there was an increased incidence of malpigmentation of the eye and skin. Subtle changes in underlying digestive and developmental physiology were revealed by microarray analysis of RNA from control and experimental fish given microdiet from day 20 post first feeding. Fifty-eight genes were differentially expressed over the four sampling times in the course of the trial and the 28 genes with annotated functions fell into five major categories: metabolism and biosynthesis, cell division and proliferation, protein trafficking, cell structure, and stress. Interestingly, several of these genes were involved in pigmentation and eye development, in agreement with the phenotypic abnormalities seen in the larvae.     

Growth and respiration of embryos and larvae of the rabbittish Siganus randalli (Pisces, Siganidae)

Growth and respiration of larval rabbitfish from Guam were examined. Larvae were reared from eggs in 2- to 10-ton tanks and were fed rotifers, Anemia , and artificial feed in succession as development proceeded through metamorphosis. Growth in length was rapid during the 12 h after hatching, then slowed until the larvae began to feed. The yolk sac was usually absorbed by 36 h after hatching. Rates of respiration of larvae and eggs were determined with a dissolved oxygen electrode at various times through development. Larval metabolism increased steadily during the embryonic stages culminating in a metabolic burst immediately after hatching. Respiration rates remained relatively stable from shortly after hatching until the onset of exogenous feeding, after which respiration rates increased with larval size. The respiration rates of post-yolk-sac larvae scaled isometrically with larval dry mass. Daily growth of feeding larvae was 27 to 28% of larval dry mass.     

Diet breadth variability in larval blue whiting as a response to plankton size structure

Diet breadth (measured as the S.D. of the log of prey size per larvae; SLH) of blue whiting micromesistius poutassou larvae followed a quadratic equation with larval size. In small larvae, diet breadth in terms of size (SLH), the mean and the maximum of the log of prey size per larvae (MLH and XLH, respectively) increased with larval size as prey size selection shifted to larger prey. In contrast, large larvae tended to reduce diet breadth of prey sizes ingested, focusing on the larger prey that were abundant, instead of raising the upper limit of prey sizes because of the low abundance of larger prey. Except for larvae at the onset of first feeding, number of prey stayed constant or decreased in relation to larval size. Both patterns (in small and large larvae) maintained a constant rate of increase of gut carbon content with increase in larval size. Large larvae appear to maintain the increase in gut carbon content during ontogenetic development by reducing diet breadth (SLH) and increasing selection towards the larger prey that are abundant.     

Relationship between specific dynamic action and protein deposition in calanoid copepods

The link between specific dynamic action (SDA) and protein deposition was investigated in copepodites stage V of two calanoid copepod species, the neritic Acartia tonsa and the oceanic Calanus finmarchicus. This was done by measuring respiration before, during, and after a specific feeding period and measuring the incorporation of carbon into proteins. These were also measured on individuals incubated with cycloheximide, an antibiotic that inhibits protein synthesis. The cycloheximide treatment significantly diminished the magnitude of SDA in both A. tonsa and C. finmarchicus, and inhibited carbon incorporation into protein in both species. This provides evidence that the rate at which protein deposition takes place greatly affects the magnitude of SDA. The specific respiration rates of both starving and feeding copepods were generally higher in A. tonsa than in C. finmarchicus. This influenced SDA, the magnitude of SDA normalised to an 8 h feeding period being threefold higher in A. tonsa (78.7+/-25.7 nlO(2) μgC(-1)) than in C. finmarchicus (27.5+/-11.6 nlO(2) μgC(-1)). This difference may arise due to differences in energy allocation in the organisms of the copepodite V stage of the two species. In this stage C. finmarchicus deposits large quantities of storage lipids, predominately wax esters, whereas A. tonsa deposits proteins during somatic growth.     

Cholecystokinin (CCK) in Atlantic herring (Clupea harengus L.) - ontogeny and effects of feeding and diurnal rhythms

Neural and alimentary cholecystokinin (CCK) levels in Atlantic herring, Clupea harengus, were analyzed from hatching to 40days after hatching (DAH). The head compartment representing the neural pool was quantitatively dominant (>80% of the total CCK content) while the digestive tract pool represented 6-10%. During ontogeny the CCK level in whole larvae increased almost 15-fold from 0 to 40 DAH, being particularly marked from 14 to 20 DAH. Larvae of 24 to 26 DAH were examined for potential occurrence of a circadian rhythm and to analyze the effects of feeding. Fed and fasted larvae were significantly different, where fed larvae showed higher CCK levels. There were large fluctuations in CCK levels analyzed at 3h intervals without an apparent diurnal pattern. Shorter sampling intervals of 1h in the morning when lights were switched gradually on and food was offered to the larvae demonstrated a marked drop in the relative gut CCK levels and a concurrent increase in the CCK carcass to gut ratio, 1h after introduction of food followed by a return to prefeeding levels after 2h. This response probably results from a release and re-synthesis of CCK in the gut after initiation of feeding. Taken together, these results support earlier reports that CCK participates in the regulation of digestive processes in herring larvae, but CCK does not seem to have a circadian rhythm independent of feeding.     

The effect of starvation on RNA: DNA ratios and growth of larval striped bass, Morone saxatalis

Hatchery reared larval striped bass, Morone saxatilis , 8-days-post-hatching were subjected to various feeding/starvation regimes over a period of 14 days.
Batches of larvae from each treatment were sampled over the 14-day period and subdivided for determination of notochord length and RNA:DNA ratio. The best growth was found in fully fed F1000 larvae (exposed to 1000 Artermia nauplii l⁻¹), which reached 8.2 mm after 11 days and 9.6 mm after 14 days. Starved animals after 11 days had notochord lengths of 4.9 mm. Growth curves from feeding-delayed larvae indicated that animals fed after up to 5 days starvation were capable of complete recovery. F100 larvae (exposed to 100 Anemia nauplii 1^−l) had a slower growth rate than F1000 larvae, reaching a notochord length of 7.3 mm after 14 days. RNA:DNA ratios over time closely followed notochord growth curves, with clear differences between starved, F100 and F1000 larvae being established after only 2 days. Equilibrium RNA:DNA ratios of 3.0 and 2.25 were established in F1000 and F100 larvae, respectively, 6.8 days after the beginning of the experiment. The average lag time between a change from the starved to the fed condition and a change in RNA:DNA ratio as determined by the divergence of the nucleic acid curve from the starved condition was 0.66 days.
In treatments where starvation followed various periods of feeding, larvae regressed in notochord length such that the final length at 14 days reflected the degree of feeding. RNA:DNA ratios in these animals again closely followed growth curves with a lag time of 0.81 days.
It was concluded that RNA:DNA ratios provided very accurate indices of growth in striped bass larvae which were highly sensitive to feeding status.     

Characterization of Serine Proteinase Inhibitor from Subabul (Leucaena leucocephala Lam) Seeds

Partially purified subabul trypsin inhibitor (STI) showed high level of thermotolerance and pH stability with a molecular weight of -15 kD. Bioassay results showed that STI is a strong inhibitor of Helicoverpa armigera larval gut proteinases. In vitro feeding experiments revealed 40% mortality in inhibitor fed larvae followed by 12 days extension in larval growth period and significant reduction in pupal weight. Differential activity staining for the larval gut proteolytic enzymes did not show any difference in the isoprotease pattern between the control and the larvae fed with STI.     

Consumption and gut evacuation rate of laboratory‐reared spotted seatrout (Sciaenidae) larvae and juveniles

The temperature and mass dependence of maximum consumption rate was measured for larval and early juvenile spotted seatrout Cynoscion nebulosus . Maximum consumption ( C _MAX) estimates were obtained from feeding and gut evacuation experiments on larvae (3·8–19 mm standard length, L _S) at three temperatures (24, 28 and 32° C), and maximum consumption experiments on juveniles at three temperatures (20, 26 and 32° C). Feeding levels were determined for larvae fed live prey ( Brachionus plicatilis and Artemia salina ) ad libitum . The midgut and total evacuation times were estimated for fish feeding continuously and discontinuously using alternate meals of tagged and untagged live prey. Temperature and fish size had significant effects on gut evacuation and consumption. The gut evacuation time increased with increasing fish size, and decreased with increasing temperatures. Mass‐specific midgut contents increased for small larvae <0·156 mg dry mass ( M _D)( c . 4 mm L _S), and decreased for larger larvae and juveniles. Maximum consumption was modelled by fitting a polynomial function to a reduced dataset of individuals feeding at high levels. The C _MAX model predicted an initial increase in specific feeding rate from 70 to 155% M _D day⁻¹ for small larvae, before declining for larger larvae and juveniles.     

Effect of nematode Panagrellus redivivus density on growth, survival, feed consumption and carcass composition of bighead carp Aristichthys nobilis (Richardson) larvae

The study aimed to determine the optimum density of free‐living nematodes in feeding bighead carp, Aristichthys nobilis, larvae. In the first experiment, carp stocked at 25 larvae L^?1 were fed varying levels of nematodes (50, 75, 100, 125 and 150 per ml) twice a day for 21 days from the start of exogenous feeding. Final body weight was significantly higher (P < 0.05) in larvae fed 125 and 150 nematodes per ml than in those fed 50 and 75 per ml, but survival was low (61.8 and 63.6%, respectively). Survival rate was highest in larvae fed 100 nematodes ml^?1 (81.3%). Carcass analysis showed that larvae fed 125 and 150 nematodes ml^?1 had significantly lower body protein and higher body lipid than those fed other nematode densities. Carcass ash was similar for larvae fed 50–100 nematodes ml^?1 but it decreased significantly at the higher nematode densities. Carp larvae in a subsequent experiment were given 50, 75 and 100 nematodes ml^?1 per feeding. Newly hatched Artemia was the control feed. Nematode consumption and growth of the larvae were determined. Larvae were sampled at intervals of 2–4 days and the nematodes in the gut were counted and measured. At each nematode density, the number of nematodes present in the gut of the larvae increased significantly with time. At each sampling day, the number of nematodes in the gut did not differ significantly among treatments (P > 0.05) although it tended to increase with nematode density at day 2 and day 4 but decrease at day 7 onward. The carp larvae consumed significantly shorter nematodes on day 2 and day 4 than on the succeeding sampling days regardless of nematode density. However, the length of nematodes in the gut of the larvae did not differ significantly among the nematode densities. The final body weight of larvae increased with increasing nematode density. The body weight of larvae fed 100 nematodes ml^?1 did not differ significantly from that of larvae given Artemia nauplii. Results show that bighead carp larvae should be fed 100 free‐living nematodes per ml at each feeding time.     

The mustard trypsin inhibitor 2 affects the fertility of Spodoptera littoralis larvae fed on transgenic plants

The effects of mustard trypsin inhibitor MTI-2 expressed at different levels in transgenic tobacco lines have been evaluated by feeding the lepidopteran Spodoptera littoralis throughout its larval life. Specific conditions were selected to study the long-term effects of feeding larvae on transgenic plants expressing the inhibitor at various levels. The data obtained led to the establishment of three relevant parameters to be considered during the experimentation: (i) the PI content of the plant lines to be used; (ii) the developmental stage of larvae sensitive to that PI content; (iii) the ratio of MTI-2/proteases sufficient to inhibit gut proteases. The experimental data obtained from feeding S. littoralis larvae using these conditions led to two main results. First, when L2 S. littoralis larvae were fed on high MTI-2 expressing tobacco plants, no effects on larval development were detected but there was a significantly reduced fertility. When the same larvae were fed on low expressing MTI-2 tobacco plants, only a less marked lowering of fertility was observed. Second, after the first generation, no differences in protease activity were observed in insects derived from larvae fed on high or low MTI-2 expressing tobacco lines, suggesting that genetic traits observed in previous studies were not inherited.     

Feeding behavior of neonate Ostrinia nubilalis (Lepidoptera: Crambidae) on Cry1Ab Bt corn: implications for resistance management

The European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae), is an economically important insect pest of corn, Zea mays L., in the United States and Canada. The development of genetically modified corn expressing genes derived from Bacillus thuringiensis (Bt) that encodes insecticidal crystalline (Cry) proteins has proven to be effective in controlling this insect. To assess the feeding behavior of neonate O. nubilalis on Bt corn, we examined differences in feeding behavior, based on presence of plant material in the gut, between Cry1Ab Bt corn and non-Bt near isoline corn for four intervals over a 48-h period. Feeding experiments revealed that there was significantly less feeding on Bt corn compared with non-Bt near isoline corn. The behavior of neonates on the plant corresponded with the differences in feeding on the two corn lines. The findings also showed that > 50% of the larvae initially left the plant before there was evidence in the gut of feeding regardless of whether the source was Bt or non-Bt corn. A higher quantity of plant material was found in the gut of larvae recovered from leaves of non-Bt compared with Bt corn. At the end of 48 h among the larvae that had left the plant, a greater proportion from Bt corn had plant material in the gut than did those from non-Bt corn.