Larval Capture Research Articles

Guiding the path of larvae: The potential of light traps in Neotropical freshwater fish research

Light traps are devices utilized in biomonitoring studies across various aquatic environments. Although light traps are used globally, few studies report their efficacy in capturing fish larvae in the Neotropics. To address this gap, this study aimed to assess the efficacy of light traps in capturing larvae of six fish species commonly found in Neotropical rivers. Additionally, we aimed to evaluate the effect of light color on larval capture. To accomplish this, we selected larvae from six species: Cyprinus carpio, Ctenopharingodon idella, Piaractus mesopotamicus, Pimelodus maculatus, Prochilodus lineatus, and Rhamdia quelen. Each experiment lasted seven days, and six types of traps were tested, including those without light (control) and those with light (green, red, yellow, white, and blue), and installed in triplicate. A total of 18 traps were randomly positioned in earthen ponds containing the six species of interest. Each species was assessed separately in six experiments. Larvae were counted, measured, and identified daily according to their developmental stage. The light traps collected 30,498 larvae, whereas the control traps only collected 39 larvae by the end of the experiment. Larvae from species of the Cypriniformes order were the most captured, while those from the Siluriformes order were least captured. The light traps exhibited selectivity in capturing larvae at different developmental stages, which varied according to species. Traps installed with green lights captured a greater number of larvae and were more efficient at capturing larvae from a wider variety of species. In contrast, traps installed with red light led to the capture of fewer larvae. Therefore, by their ability to attract a greater number of larvae, compared to control, and selectively capture larvae at different developmental stages at variable rates, depending on light source, light traps can be a valuable tool in biomonitoring and managing fish larvae in Neotropical environments.

Calling for institutional arrangements in Napoleon Wrasse conservation and management in Indonesia: The Anambas Islands case

Cheilinus undulatus, or Napoleon wrasse – though severely vulnerable to extinction - has become a highly sought-after luxury food for certain societies and has intensified its continuous market demand. Overfishing has been the key factor driving the collapse of its populations. Therefore, conservation and management have never been more urgent. This study explores Napoleon wrasse farming in Anambas, Indonesia. Data gathering was conducted through interviews, exploring the farming practices and export trade. The findings are showing the history of overfishing of adult fish, leading to larval capture as the tragedy of the commons in the nursery grounds. Farming practices causing no stocks replenishment. The government supports the promotion of sustainable activities such as spatial protection. LMMA shows the success of community based coral reef rehabilitation, and this bring opportunity to local communities to utilize Napoleon fish other than farming. However, even though spatial protection leads to institutional arrangement to control unsustainable practices, it needs an integration with calculation based on science to determine the sustainable export quota. Unfortunately, the Non Detriment Findings on Napoleon fish trade was not based on biological assessment, so even though the recent export practice is legal, but it cannot be considered as sustainable. It is also important to allocate the benefit of the farming to broader group so the power of the dominant becomes uncentralized. The more benefit earned by the farmers from sustainable fishery, the more easier it is to institutionalize social norms to avoid overfishing and achieve the conservation goals.

Laboratory and Field Evaluation of an innovated adult-larval mosquito trap for the capture of dengue vector mosquitoes

The exact dates of the introduction of Aedes aegypti and dengue in the Philippines are unknown; however, the first records of the circulation of dengue in the Philippines among accounts from military hygiene records after the Philippine-American War were recorded in 1903 among U.S. soldiers stationed in bases in Manila. So dengue has long been confronting the country, but in 1953, dengue hemorrhagic fever was reported for the first time in this part of Asia. From then on, sporadic dengue cases have been reported in several parts of the country, and control measures were instituted only when necessary. Three (3) trap prototypes, trap x, y, and z, with different trap entrances, were tested for both adult and larval capture of dengue vector mosquitoes in the laboratory and field. Prototype trap x had openings for capture at the sides, prototype y had both side and top outlets for capture, and prototype z had a top entrance only for capture. Release-and-recapture testing on the three trap prototypes revealed that prototype x (side entrance only) captured more Aedes mosquitoes at a low (n=3) to medium (n=25) number of mosquitoes released. Trap z (with top mosquito entrance only) captured more mosquitoes at high densities (n=50). In the field, capture performances on Aedes dengue vector mosquitoes had no significant differences, including the comparator, Ovicatch™. Non-target mosquito capture and non-mosquito capture were comparatively lesser than the capture of Aedes aegypti and Aedes albopictus. The prototype x showed Aedes capture performance most comparable to Ovicatch™.

Capture of conspecific planktonic larvae by the suspension-feeding gastropodCrepipatella peruviana: association between adult and larval size

ABSTRACTFree-living, planktonic larvae can be vulnerable to capture and ingestion by adult suspension-feeders. This is particularly the case for larvae that settle gregariously in benthic environments where suspension-feeders occur at high densities. Larvae of gregarious suspension-feeding species are at particularly high risk, as adults of their own species often serve as cues for metamorphosis. We conducted laboratory experiments to assess the extent to which adults of the suspension-feeding caenogastropod Crepipatella peruviana would capture and ingest their own larvae. Experiments were conducted with adults of different sizes, with larvae of different ages and sizes, and in the presence or absence of phytoplankton. Adults captured larvae in all experiments. The presence of microalgae in the water did not influence the extent of larval capture. On average, 39% of larvae were captured during the 3-h feeding periods, regardless of adult size. However, up to 34% of the larvae that were captured on the gill were later discarded as pseudofaeces; the other 64% were ingested. The extent of capture by adults was not related to adult size, or to larval size and, thus, to larval age. Our results suggest that the filtration of congeneric larvae by adult C. peruviana is a result of accidental capture rather than a deliberate feeding preference. Such ingestion could, however, still be an important source of larval mortality, especially when the advanced larvae of this species are searching for a suitable substrate for metamorphosis.

Suitability of Tisochrysis lutea at different growth phases as an enrichment diet for Brachionus plicatilis sp. complex rotifers

In larviculture of marine finfish, Tisochrysis lutea cultured cells have a potential to be a sustainable enrichment diet for rotifers due to its de novo synthesis of docosahexaenoic acid (DHA). To improve its effectiveness in rotifer enrichment for later larviculture, we determined which growth phase of T. lutea can enhance DHA in polar lipids (PLs) in Brachionus plicatilis sp. complex rotifers without reducing their vigor. Tisochrysis lutea was harvested at logarithmic growth phase, deceleration growth phase, and stationary phase. The ambient concentrations of phosphorus (P) and nitrogen (N), and fatty acid composition of microalgae were measured. P was limited between logarithmic and deceleration growth phases, followed by N starvation in stationary phase. Total lipid DHA was lowest in logarithmic growth phase, whereas DHA levels increased in deceleration growth phase and maintained at high levels even in stationary phase. PL-DHA also increased during deceleration growth phase, although its abundance dropped during stationary phase. In a rotifer enrichment trial, T. lutea harvested in each phase were fed to B. plicatilis sp. complex rotifers for 12 h. The highest PL-DHA value for cells in deceleration growth phase reflected the concentrations of the rotifers. No significant differences were found in rotifer growth rate and egg ratio. Rotifers fed cells in deceleration growth phase exhibited higher swimming speeds than those fed the other cells, potentially linking to increased larval capture success. Therefore, we recommend the deceleration growth phase as an optimal timing for T. lutea harvest for the effective enrichment of B. plicatilis sp. complex rotifers.

Timing and Location of Spawning Based on Larval Capture and Ultrasonic Telemetry of Atlantic Sturgeon in the Saint John River, New Brunswick

AbstractThe timing and location of spawning of Atlantic Sturgeon Acipenser oxyrinchus oxyrinchus were investigated using larval sampling and ultrasonic telemetry in 2010–2014 in the lower Saint John River, New Brunswick, Canada. Larval sampling was conducted to identify potential spawning areas using anchored D‐frame drift nets and towed bongo nets. Forty‐four adult Atlantic Sturgeon (138–213 cm) were ultrasonically tagged and passively tracked using hydrophone receivers located throughout the river. Spawning was confirmed with the first capture of Atlantic Sturgeon larvae in the river. Four Atlantic Sturgeon yolk sac larvae (13.44–14.43 mm) were captured on July 23, 2011, and one exogenous feeding larva (22.6 mm) on July 25, 2011, at river kilometer (rkm) 106 near Burton, New Brunswick. Spawning time was estimated using larval growth models and is likely to have occurred July 6–13, 2011, above rkm 106. Eleven tagged fish returned to the river in May and June after a minimum of 2 years at large: nine males, one female, and one unknown sex. Seven of the 11 returning fish migrated to potential spawning areas above rkm 100. Based on the upstream occupancy observed, annual variability in spawning time is likely. The other four fish that returned remained below the salt–fresh interface with brief upstream migrations below rkm 100, suggesting that some fish are not spawning during summer migration. The majority of fish migrated from the river in August and September. This study provides the first description of the location and timing of Atlantic Sturgeon spawning and migratory patterns in the Saint John River.Received April 3, 2016; accepted November 17, 2016 Published online February 1, 2017

Evidence of selection for resistance to paralytic shellfish toxins during the early life history of soft‐shell clam, Mya arenaria, populations

This study identifies early, postmetamorphic soft‐shell clams, Mya arenaria, as the life‐history stage most susceptible to effects of blooms of paralytic shellfish poisoning (PSP) toxin–producing Alexandrium spp. Laboratory experiments used progeny from predominantly susceptible (naϊve) or resistant (annually exposed) NW Atlantic populations. Growth and survival of toxified veliger larvae did not differ from those fed nontoxic algae. In contrast, postlarvae (4–12‐mm shell length) from both populations exposed to a highly toxic Alexandrium tamarense isolate (~ 100 cells mL−1, 64–69 pg saxitoxin equivalents [STXeq] cell−1) suffered burrowing incapacitation, toxin accumulation, and mortalities within 1 week of toxin exposure. These effects were greater and occurred sooner in the naϊve population. Short‐term toxification in the laboratory caused a significant shift in the genotypic composition of this population, determined with a molecular marker for sodium‐channel resistance. Clams with the sensitive genotype were selectively eliminated relative to resistant or heterozygote clams. Ingestion of toxic cells (too large for larval capture) is thus required to elicit toxic effects. Exposure to mixed, toxic, and nontoxic algal suspensions demonstrated that adverse effects to fitness (survival and growth) were dose‐dependent, occurring only at ≥ 50 cells mL−1 of the isolate used (PR18b). Paralysis and thus increased predatory risk occurred even at 10 cells mL−1. Postlarvae < 12 mm, which can co‐occur with red tides throughout the Atlantic range of M. arenaria, were more susceptible to PSP than large (> 30 mm) juveniles. Natural selection for resistance in Atlantic populations will thus vary latitudinally with the timing, duration, and intensity of toxic blooms.

Monitoring <I>Tribolium castaneum</I> (Coleoptera: Tenebrionidae) in Pilot-Scale Warehouses Treated with Residual Applications of (<I>S</I>)-Hydroprene and Cyfluthrin

Pilot-scale warehouses, artificially infested with all life stages of Tribolium castaneum (Herbst), were used to evaluate the efficacy of two contact insecticides, (S)-hydroprene and cyfluthrin, and to determine the effect of insecticide treatments on insect captures in food- and pheromone-baited pitfall traps. Two application strategies were compared; insecticides were applied at the labeled rate either around the inside perimeter of the warehouse or in a band around the base of shelf units containing discrete food patches (10 g of wheat flour) infested with T. castaneum. Insect populations were assessed weekly for 6 wk by recording number of dead adults on the warehouse floor; number of larvae and adults captured in pitfall traps; and number of larvae, pupae, and adults recovered from food patch samples. There were significantly more dead adults in warehouses treated with cyfluthrin than with (S)-hydroprene or water (control treatment). However, food patch samples showed no detectable differences in quantity of larvae, pupae, or adults among any treatments. Pitfall traps detected fewer larvae starting the fourth week of the study in the warehouses treated with cyfluthrin around the shelf perimeter. Rate of larval capture in traps increased overall with increasing larval populations, but it was more pronounced in traps located closer to the food patches. Number of adults captured in pitfall traps reflected adult mortality in cyfluthrin-treated warehouses. Capture of larvae and adults was greater near the source of the infestation than elsewhere in the warehouse, suggesting that trapping data should be considered when precision targeting insecticide applications in the field.

Assessment of a trap for measuring larval supply of intertidal barnacles on wave-swept, semi-exposed shores

Larval supply and settlement of Semibalanus balanoides (L.) on a semi-exposed wave-swept shore in E Scotland were assessed by means of a new larval trap design. Two midshore sites were utilised throughout the peak of the 2001 settlement season (May 11–June 3). Larval supply was quantified by 176 ml baffled cylinder traps filled with a 4-M killing solution of urea in seawater. Larval trap washout of urea typically ranged from ∼25% per day under minimal wave action to a maximum of 39% under heavy wave action during an onshore gale. The maximum capture for a single trap was 334 cyprids over one tide. Significant and consistent positional effects, both on urea retention and larval capture, were found for replicate traps separated by 9 cm. These indicated fine-scale variations in hydrodynamic flow and larval supply over the substratum which will have implications for the quantification of spatial heterogeneity of larval input to the benthos. The retention of urea and larval capture efficiency generally were not compromised by traps being serviced daily, as opposed to tidally, except perhaps for captures at very low larval densities. Larval supply measured on a tidal basis was strongly correlated between sites ( r=0.975), but supply at Site C was ∼5× that at Site T: the reduction at Site T could not be explained by its slightly shorter immersion time and hence ‘availability’ of cyprids alone. At Site C settlement was quantified for 5×5 cm quadrats of natural substratum cleared daily. Settlement on these clearances (subject to possible grazing by limpets) was quantified only from May 20–June 3, after the peak of larval supply on May 17, and the variation in larval supply explained 65% of the variance in settlement. The larval supply/settlement relationship at Site T was quantified using grooved acrylic panels. A high correlation coefficient (0.961) was obtained for the daily supply/settlement relationship for these panels over the period May 15–June 3, which included the peak of supply. Larval supply varied up to 15-fold within a site on consecutive tides and up to 100-fold between sites on the same tide. Although further improvements to both the larval trap and the settlement panels can be made, this larval trap does appear capable of providing high-resolution data on tidal or daily larval supply over a wide range of wave conditions and larval concentrations.

Modified Larval Bait Trap for Sampling Black Cutworm (Lepidoptera: Noctuidae) Populations in Field Corn1

A cutworm larval bait trap was improved for sampling black cutworm populations in field corn. Trap size was reduced from 1.98 to 0.41 liters without substantially reducing trap efficiency. A removable inner cup was used to reduce the quantity of vermiculite which must be searched for thc retrieval of cutworms. Four trap components used in the original trap were adapted to the modified trap and evaluated. Two of these components, cylinders and wheat bran, had a significant effect on larval capture, whereas metal guides and lids had little or no effect and were not incorporated into the modified trap design.

The Larval Dwelling-tube, Capture Net and Food of Phylocentropus placidus (Trichoptera: Polycentropodidae)

In Georgia, the larvae of Phylocentropus placidus Banks) construct branched elongate tubes composed of very fine sand grains which are largely buried in detritusladen sandy stream beds. A vertical tube, with a small sub-apical opening for incurrent water, protrudes several centimeters above the stream bed. The lower part of this vertical tube extends into the stream bed as far as 12 cm. Below the substrate surface the vertical tube has branch attached at a 90° angle that curves upward to the surface of the stream bed. This latter branch contains an enlarged chamber that houses the larval capture net. At the apex of this branch there is a small opening for excurrent water. The capture nets have no distinct uniform mesh shapes; instead, there is a random arrangement of closely placed layers of silk strands. Larvae apparently force water through the tubes by undulating their bodies. Larvae feed primarily on very small particulate detritus particles with an avg plane surface area of about 48 μ (or about 7 μ diam). Larval dwelling tubes are found in deposition areas of meandering streams, and Phylocentropus is the only net-spinning trichopteran to inhabit such areas in these streams. The dwelling tubes are very similar to those of the genus Protodipseudopsis described previously from Africa and supports the recent transferral of Phylocentropus from the sub-family Polycentropodinae to Dipseudopsinae.

The Larval Retreat and Food of Arctopsyche; with Phylogenetic Notes on Feeding Adaptations in Hydropsychidae Larvae (Trichoptera)

Arctopsyche larvae generally construct somewhat cornucopia-shaped dwellings at the top and sides of large rocks in swift mountain streams and spin a capture net across a U-shaped frame at the anterior end of the larval abode. There is an increase in net mesh size in successive larval instars. The individual meshes of mature larval capture nets are the largest found to date in the Hydropsychidae. Based on larval foregut contents, 2nd instars are about 50% plant detritivores and 50% predators. In the last 2 instars foregut contents consisted of ca. 90% insect fragments and 10% plant material. The structure of the nets and larval abodes supports the placement of the Arctopsychinae as primitive Hydropsychidae. In the evolution of hydropsychid larvae there is a tendency toward more complicated larval feeding structures and smaller capture net mesh sizes.