Juvenile Production Research Articles

Assessing the population impacts and cost‐effectiveness of a conservation translocation

Abstract Managers often move, or translocate, organisms into habitats that are assumed to be suitable; however, the consequences of these translocations are usually not rigorously assessed. Robust assessment of these management experiments should consider impacts to both donor and recipient populations and compare the cost‐effectiveness of translocations to other actions. Here we evaluate the translocations of a federally listed fish species, humpback chub within a tributary to the Colorado River in its Grand Canyon reach (Arizona, USA). We analyse mark–recapture data with multistate models to estimate vital rates (growth, survival and movement) for the donor and recipient populations while accounting for substantial temporal variation in vital rates. We then use stochastic matrix projections to quantify the impact of translocations on adult population size. Lastly, we compare the costs of translocations to another, legally required management action, non‐native fish removal, by modifying an existing bioeconomic model. We estimate that six of eight translocations during the study period positively impacted adult abundance and that the overall population impact was positive. Population projections suggest that each chub translocated per year increases the equilibrium adult population size by 1.2 (95% CI: 0.4–2.2) adults, lessening the need for non‐native fish removal. The continuation of translocations at the current rate is expected to save managers ~$50,000 per year by decreasing the annual probability of removals from 0.26 to 0.15. Further savings and decreases in removals could be attained by avoiding translocations in years when there has been no winter/spring runoff and modifying the number of translocated individuals based on the estimates of juvenile production in the lower Little Colorado River. Synthesis and applications. Translocations that increase the abundance of a rare species can sometimes be viewed as a hedge against future declines that might necessitate more costly interventions. Quantifying population benefits and economic costs of management actions like translocations and comparing alternative actions can lead to cost‐effective conservation that is more easily sustained.

Effect of microencapsulated phenolic compound extracts of Maclura tinctoria (L.) Steud on growth performance and humoral immunity markers of white leg shrimp (Litopenaeus vannamei, Boone, 1931) juveniles

Aim of study: The effect of microencapsulated phenolic compound extracts of Maclura tinctoria (MTBE) on growth performance and humoral immunity markers of the white leg shrimp Litopenaeus vannamei juveniles (0.5 ± 0.2 g initial weight) was studied.Area of study: M. tinctoria was collected from Hampolol, Campeche, and Arroyo del Agua, Culiacan, Sinaloa, Mexico.Material and methods: Three MTBE inclusions (0.5, 1, and 2.5 g MTBE/kg, Purina®) were compared with a control commercial feed (Purina®) during 30 days. Nine phenolic acids, nine flavonols, four dihydro-flavonoids, four flavones, and seven unidentified phenolic compounds were determined fin the MTBE using a Perkin Elmer® HPLC chromatograph and diode array-detection.Main results: The mean concentrations of total phenolic compounds, total flavonoid compounds, and condensed tannins were 198.05 ± 5.59 mg gallic acid equivalent (GAE) g-1 dw, 78.57 ± 1.80 quercetin equivalent g-1, and 28.32 ± 0.33 mg epicatechin equivalent g-1, respectively. The ferric reducing antioxidant power and the total antioxidant capacity, respectively, averaged 28.32 mg GAE mL-1 and 10.9 mg ascorbic acid equivalent mL-1. Survival, weight gain, and specific growth rate of L. vannamei were similar among the experimental diets. The dietary inclusion of MTBE at 0.5 g/kg of food showed significant higher (p < 0.05) plasma hemocyte lysate protein (1.35 ± 0.055 µg mL-1), prophenoloxidase (0.47 ± 0.15, Abs. 492 nm), and superoxide anion (O2.-) activity (0.21 ± 0.07, Abs. 630 nm).Research highlights: The supplementation of MTBE at 0.5 g/kg of food could be considered as a potential alternative additive for L. vannamei diet in the juvenile production, since it improved the response of the humoral immunity markers at post larval life stages, when cultivated shrimp are more susceptible to be infected by pathogens.

Factors affecting the spatio-temporal variability in the production of sandfish Holothuria scabra juveniles in floating hapa ocean nursery systems

Hatchery production of the tropical sea cucumber Holothuria scabra or sandfish has been successfully demonstrated in various countries, especially during the past decade. However, the main bottleneck in up-scaling production of larger sandfish juveniles is in the nursery phase where land-based facilities are limited in the Philippines compared to other countries. This has led to some promising pioneering research in ocean-based sandfish nurseries in the Philippines. However, site-specific and seasonal inconsistencies in production levels were observed. In this study, a comprehensive experiment comparing 17 replicated nursery culture operations of sandfish juveniles using floating hapas, was conducted across four sites with distinct geo-climatic zones in the Philippines and at different months from 2013 to 2016. We evaluated the performance of the ocean-based floating hapa nursery system by determining the effects of periphyton characteristics and broad-scale differences in meteorological variables to growth and survival of juvenile sandfish within different geo-climatic zones. Our data confirmed high spatial (across sites) and temporal (among trials within a site) variability in sandfish culture performances. Wind stress was the most significant driver of this variation, which negatively influenced growth and survival of juveniles especially during Cycle 1 (first 30 d). Sandfish growth was positively related to Chl-a and mean temperature, but was negatively impacted by Wind stress, Autotropic Index (AI), total rainfall (∑Rain), and sea-surface atmospheric pressure; while survival was positively affected by phaeophytin and Ash-Free Dry Weight (AFDW) content of the hapa biofilm. In Cycle 2 (succeeding 31–60 d), growth and survival was greatly influenced negatively by the re-stocked density (number of individuals surviving from Cycle 1), while survival was further affected negatively by ∑Rain and AFDW. Our results provide significant information on suitable ocean nursery conditions, periphyton/biofilm characteristics, and spatial-temporal considerations for optimizing production of H. scabra juveniles in floating hapas. We also highlight the negative effects of increasing biomass density when on-growing larger juveniles in this system. These insights are valuable in optimizing management and operation of ocean nurseries for sandfish, not only in various potential sites in the Philippines, but also in many developing tropical countries in the Indo-Pacific.

Feeding habits and growth characteristics of cobia (Rachycentron canadum) larval and juvenile stages

The feeding habits and growth of larvae and juveniles under artificial culture conditions were examined using the ecological method of simple random sampling to better understand the feeding characteristic of cobia (Rachycentron canadum) during the early development stage. The results showed that cobia larvae had a good foraging capability. After three days of the hatch (DAH), the larvae began feeding, and the feeding incidence was 70%. Feeding incidence was 100% in the case of juveniles. Feed intake of larvae and juveniles increases with increased body mass and could be expressed using the binomial equation (R2 = 0.9188). The digestive tract fullness coefficient of 3–24-day-old larvae and juveniles fluctuated from 0.1% to 1.0%. The larvae and juveniles of cobia were satiated within 1 h. The digestion time of larvae to rotifers and copepods was between 0.5 and 1.5 h and 0.5–2 h, respectively, while that of juveniles was 1–3 h. The daily feeding rates of larvae and juveniles were 61.38% (5-day-old), 54.18% (10-day-old), and 24.85% (24-day-old), and could be used as a reference for the daily feeding (%) of both larval and juvenile stages of cobia. The feeding patterns of larvae and juveniles showed a circadian rhythm, suggesting that they were fed during the day. The average daily growth rate of full-length larvae and juveniles aged 3 to 24 days was 35.90%, with an average daily weight gain rate of 56.97%. The relationship among total length, body mass, and age were expressed using a quadratic equation of one variable (R2 > 0.90) and a power function (R2 > 0.90) for the regression equation of body mass and full length. This study provides useful insights on the early development stage, and a reference for large-scale production of cobia larvae and juveniles.

Feeling the Squeeze: Adult Run Size and Habitat Availability Limit Juvenile River Herring Densities in Lakes

AbstractMaximum densities of juvenile river herring (Alewife Alosa pseudoharengus and Blueback Herring A. aestivalis) vary among freshwater lakes, likely due to densities of adult spawners. Differences in habitat availability and lake water quality may also contribute to variation in juvenile river herring productivity between populations, yet these relationships have not been tested across a large geographic scope. In this study we investigated relationships between juvenile river herring densities and (1) spawning adult river herring densities, (2) lake habitat availability, and (3) lake water quality in 29 freshwater lakes in the northeastern USA. Purse seines were used at night to sample juvenile river herring monthly in June–August 2014 and 2015, with concurrent collection of lake‐specific physical (e.g., lake surface area, mean depth, depth to thermocline), chemical (e.g., nitrogen, phosphorus, dissolved organic carbon [DOC]), and biological (chlorophyll a, adult spawning density) data. Spawning adult density (number of adults per surface area of lake) explained 66.6% of the variation in juvenile densities using a generalized additive model. Juvenile densities increased with increasing adult density, peaking at roughly 1,000 adults/ha, and then declined at higher adult densities, suggesting a limit to carrying capacity in juvenile production. Linear mixed‐effects models revealed that differences in water quality and habitat across lakes explained additional variation in juvenile densities. Specifically, DOC was negatively related to juvenile densities, suggesting that DOC limits the amount of suitable, well‐oxygenated epilimnion habitat available to juvenile river herring in late summer. Our results can be used to help understand expected juvenile production based on adult density within a lake, to inform expectations about juvenile growth and survival, and to understand the mechanisms for how changes in habitat availability and water quality affect river herring populations.

Influence of tank shading and rearing density on growth during stunted juvenile production of rohu, Labeo rohita (Hamilton)

Seed stunting of rohu, Labeo rohita (Ham.) carried out for 6 months in 24 large (50 m2) concrete tanks using 20 and 40 fry m−2 rearing densities under open and shade (50% light incidence) conditions. A significant influence of tank shading observed on all the water quality parameters, unlike the density effect only on the dissolved oxygen content in water. Highly significant stunting effects of both higher density and shading observed on juvenile growth and survival after 2-, 4- and 6-month stunting. Doubling the density caused 22.9 and 27.8% weight suppression after 6-month stunting under open and shaded conditions respectively. Similarly, shading caused 31.7 and 36.1% suppressed body weight after 6 months in the low- and high-density groups respectively. However, the best stunting effect observed through a compounded effect of high density and shading as 50.7–57.0% growth suppression recorded within 2–6 months stunting. The study revealed both higher rearing density (two times) and tank shading (50% light incidence) to be effective tools for rohu juvenile stunting, while a combination of these factors yielded greater stunting effect. Such protocol can be used for production of stunted carp juveniles to ensure their round-the-year availability for stocking grow-out ponds.

Population changes and limitation in the montane vole (Microtus montanus) in perennial old-field grasslands: insights from a long-term study

AbstractWe livetrapped populations of Microtus montanus from 1982 to 2003 in semiarid perennial old-field grasslands of southern British Columbia. We evaluated two, nonmutually exclusive hypotheses (H) to explain their population dynamics: first (H1), that extended breeding during the summer or winter will drive the increase phase of population fluctuations; and second (H2), that density-dependent depression of juvenile survival will be reflected in poor early juvenile survival during high populations. Populations on 2–3 grids of 1 ha were livetrapped at 3- to 8-week intervals in summer and winter except in 5 years of very low populations. Densities ranged from 10/ha to 250/ha. Peak densities occurred in 6 years and an extended low phase occurred from 1999 to 2003. Fluctuations of 3–4 years appeared in our populations but were not always present. Breeding occurred both in summer and winter, and the best predictor of the population growth rate was the fraction of adult females lactating in summer or winter, thereby supporting H1. Juvenile production (number of juveniles/lactating female) varied greatly among years with the mean being over two times higher in low (2.41) than high (1.08) years, thereby supporting H2. There was no clear correlation between population changes and either seasonal temperatures or rainfall, or any combination of these two variables, and no obvious cause of the prolonged low from 1999 to 2003. Thus, both female reproduction and juvenile production drive montane vole dynamics demographically, similar to what is found in other vole species. However, the ultimate cause of these changes remains to be tackled experimentally.

Notes on the morphology, bionomics, distribution and efficacy of Steinernema siamkayai (Rhabditida: Steinernematidae) from western Uttar Pradesh, India

Summary The entomopathogenic nematode Steinernema siamkayai has been a subject of several detailed studies but its morphological, molecular and ecological characterisation is still incomplete. In the present study we studied morphology of several strains of S. siamkayai using morphometrics and light and scanning electron microscopy (SEM) and we aimed to complete its molecular characterisation by obtaining the sequence of the D2-D3 region of the 28S rDNA in addition to ITS rDNA and mitochondrial (12S and COI) DNA studies. Furthermore, we studied the species life cycle and we attempted to assess its distribution using a meta-analysis of the GenBank records. Finally, insecticidal properties were evaluated against Helicoverpa armigera and Spodoptera litura. The SEM study revealed the presence of the adcloacal pair of genital papillae in males. Duration of the life cycle of the Indian strains did not differ from the previous records; however, we have observed production of the infective juveniles by the first-generation adults. For the first time in entomopathogenic nematodes, we have recorded intra-individual variability in the D2-D3 region of the 28S rDNA and we discuss potential implications of this phenomenon for the use of this marker in EPN systematics. Our analysis of distribution has shown that S. siamkayai is ubiquitous throughout the Indian subcontinent but is rarely found in South East Asia. The pathogenicity results showed that the present species effectively killed the tested pests under laboratory conditions, demonstrating its potential as a biocontrol agent.

Assessment of biopiles treatment on polluted soils by the use of Eisenia andrei bioassay.

A long-term case of residual pollution is studied after 20 years since the largest mining accident in Spain (the Aznalcóllar spill) happened. This pollution is manifested through a surface zoning consisting of bare soils (B0), sparsely vegetated soils (B1), and densely vegetated and recovered soils (B2). A biopiles treatment with a mixture of contaminated soils (B0 and B1) with recovered soils (B2) at 50% (w/w), and vermicompost addition (50 tons ha-1) was evaluated. To assess the effectiveness of treatments, total, water-soluble, and bioavailable fractions of the most polluting elements in the zone (Cu, Zn, As, Pb, Cd, and Sb) was analyzed. To evaluate the potential risk of contamination for the ecosystem, a bioassay with earthworm Eisenia andrei was carried out. Twenty years after the accident, there are still soils where total As and Pb exceed the regulatory levels and water-soluble Zn and As exceed the toxicity guidelines. According to toxicity bioassay, weight variation and juvenile production of earthworms showed an improvement after biopiles treatment, with values that trend to be similar to those of recovered soils. The only bioaccumulated element in earthworms was Cd (BAF>1), both in polluted as in treated soils, which indicates the possible existence of exclusion mechanisms of the other pollutants by earthworms. The comparison between biopiles and polluted soils showed no significant differences for the bioaccumulation factor of trace elements, with the exception of Zn and Cu, which slightly increased after treatment. According to our results, biopiles treatment combined with vermicompost addition is a good technique for the recovery of residual contaminated areas, by the improvement of soil properties and the reduction of the potential toxicity; anyway, monitoring of soils and organisms is needed to prevent the increase of bioavailability of some potentially pollutant elements over time.

Breeding Effort and Hydroperiod Indicate Habitat Quality of Small, Isolated Wetlands for Amphibians Under Climate Extremes

The distribution and function of small, temporarily ponded wetlands such as vernal pools are driven by climate variation, especially precipitation. These wetland ecosystems provide important habitat for amphibians, whose breeding effort (egg deposition) is often used to characterize pool habitat quality. However, whether breeding effort consistently predicts larval survival, juvenile production, and overall reproductive output—key indicators of habitat quality for amphibians in a varying environment—remains unclear. We assessed the occurrence of spotted salamander (Ambystoma maculatum) and wood frog (Lithobates sylvaticus) larvae in 71 vernal pools in New York, USA during the spring and summer of 2016 and 2017—the fifth driest and third wettest years in regional history, respectively—to better understand the relationship between breeding effort and metamorph production under environmental extremes. Breeding effort was an important predictor of whether late-stage larvae occurred in pools for both species. However, occurrence of late-stage larvae was substantially lower for both species during 2016, i.e., the drought year, when pools dried rapidly. These outcomes suggest that, in the face of an increasingly variable climate, prioritizing clusters of pools that encompass a range of hydroperiods and include high-productivity pools would help maintain populations of vernal-pool dependent amphibians.

Surface culture of Steinernema sp. on two solid media and their pathogenicity against Galleria mellonella

Abstract The use of native entomopathogenic nematodes as biocontrol agents is a strategy to decrease the environmental impact of insecticides and achieve sustainable agriculture crops. In this study, the effect of the surface culture of Steinernema sp. JAP1 over two solid media at 23–27°C on infective juvenile (IJ) production and pathogenicity against Galleria mellonella larvae were investigated. First, the bacterial lawn on the surface of the media with egg yolk (P2) or chicken liver (Cl) were incubated in darkness at 30°C for 48 and 72 h, and 100 surface-sterilized IJs were added. Four harvests were conducted within the next 35 days and the mean accumulated production was superior on Cl (210 × 103 IJs) than on P2 (135 × 103 IJs), but the productivity decreased up to 10% when the incubation time of the bacterial lawn was of 72 h. The mean pathogenicity of in vitro- and in vivo-produced IJs were of 47–64% and 31%, respectively. It is worth noting that none of the two solid media had a statistically significant difference in IJ pathogenicity. Considering that the maximum multiplication factor of IJs on solid media was 2108 and that the pathogenicity against G. mellonella was outstanding, Steinernema sp. has a good potential for in vitro mass production.

Does habitat quality matter to soil invertebrates in metal-contaminated soils?

This study investigated the influence of habitat quality (HQ) on the reproduction and bioenergetics (energy reserve and metabolic enzyme activities) of the oribatid mite, Oppia nitens, in response to cadmium (Cd). In the baseline toxicity test, Cd elevated the carbohydrate reserve of adult mites at intermediate Cd concentrations (88 and 175 mg Cd kg−1) but without a change in lipid and protein reserve across 0–700 mg Cd kg−1. The activities of glucose metabolism enzymes, glucose-6-phosphate dehydrogenase (G6PDH) and pyruvate kinase (PK) were inhibited in the mites at 700 mg Cd kg−1. Adult mites reared in high HQ soils had higher reproduction relative to mites from low HQ soils when exposed to Cd in OECD soil, but there was no difference in bioenergetics between mites from low and high HQ soils. Hence, HQ significantly (p = 0.024) influenced the reproduction of mites (i.e., juvenile production) irrespective of the Cd concentration in the OECD soil but did not significantly affect the bioenergetics of the mites. We suggest that habitat quality’s effect could be more significant than metal concentration on the biological fitness (juvenile production) of O. nitens in metal-contaminated soils.

Robust Recolonization of Pacific Lamprey Following Dam Removals

AbstractRemoval of two dams in the Elwha River basin, Washington, started one of the largest river restoration projects ever attempted in the Pacific Northwest. These dams had eliminated Pacific Lamprey Entosphenus tridentatus populations upstream. After the dam removals, larval production increased in the upper watershed, but the sources and numbers of new adult spawners were unknown. We applied genetic stock identification (GSI), parentage assignment (PA), and sibship assignment (SA) methods to (1) determine the origins of Pacific Lamprey larvae and juveniles, (2) quantify the increase in numbers of successful Elwha River spawners (i.e., effective number of breeders [Nb]) and assess whether the current numbers of spawners have reached levels equivalent to those of neighboring undammed basins, and (3) determine the relative productivity of streams within the Elwha River and how overall productivity originating from this system may be distributed across the broader surrounding region. We utilized a highly accurate set of 263 single‐nucleotide polymorphism (SNP) loci to perform PA and SA (>99% accuracy rate) and an additional set of 28 SNPs for GSI. Our results showed that a single stream (Indian Creek) was the source of 41% of larval and juvenile production in the Elwha River. Our Nb estimates for the Elwha River indicated a 12‐fold increase in Nb during the 3 years after dam removal, with recent Nb estimates matching those of neighboring Olympic Peninsula basins. These results indicate rapid recolonization potential for this highly dispersive species, and high productivity within the Elwha River suggests that restoring passage to adequate habitat is a highly effective approach for re‐establishing populations of Pacific Lamprey in coastal systems.

Standardization of oocyte size during artificial fertilization and optimization of stocking density during indoor larval and outdoor nursery rearing of captive spotted scat (Scatophagus argus) for a viable juvenile production system

The present study describes the viable and efficient hatchery seed production technique to maximize spotted scat (Scatophagus argus) juvenile production in captivity during the breeding season. Broodstock fish maintained in the earthen pond of hatchery were selected according to varying mean oocyte diameter (MOD) ranging from 351 to 400 (T1), 401–450 (T2), 451–500 (T3), and > 500 μm (T4) according to natural vitellogenesis progression. Breeding pairs were formed as two males: one female. Females (n = 24) were induced with a double dose of hCG (2000 IU kg−1 body weight day−1) and a single dose of LHRHa (400 μg kg−1 body weight) each at 24 h interval, whereas males (n = 48) received a single dose of LHRHa (200 μg kg−1 body weight). Females in T4 were spawned through dry stripping earliest at 30 h post hormone induction, whereas females of the T1 group spawned last at 33 h. The largest (P < 0.005) diameter (718.33 ± 3.28 μm) of fertilized eggs was observed in T4, whereas the smallest (652.33 ± 18.68 μm) fertilized eggs were observed in T1 post-fertilization. Significantly highest absolute and relative fecundity was found in T5 (1060.67 ± 45.36 and 213,239.7 ± 17,324.9, respectively), whereas T1 and T2 exhibited no significant difference. The dry stripped eggs were fertilized with milt and incubated for 22 h for hatching. Females in T4 achieved the greatest fertilization (98.67 ± 0.88) and hatching (97 ± 2.08) percentages significantly. The initial oocyte size range of 351–400 μm in T1 led to the lowest fertilization (17 ± 3.46) and hatching (10.67 ± 3.92) percentage. Subsequently, scat juvenile production techniques were standardized by conducting two experiments on stocking densities of larvae and fry. Hatchlings were first reared in the mesocosm larval rearing system in an indoor hatchery with four different stocking density of 2 (SD2), 4 (SD4), 6 (SD6), 8 (SD8) larvae L−1 for 30 days. Stocking density of 4 and 6 larvae L−1 achieved the highest survival of 53.05 ± 1.01% and 51.03 ± 1.23%, respectively. On completion of metamorphosis (30 dph), fry were shifted to hapa based rearing in a pond with three different stocking density of 2000 (SD2000), 3000 (SD3000), 5000 (SD5000) fry m−3 for 30 days. Highest survival percentage of 78.94 ± 2.78 found in SD3000. Present study standardized the operation protocol for a commercial hatchery aiming for juvenile scat production by selecting females with initial oocyte size >500 μm diameter for artificial fertilization. Seed production can be optimized by adopting a stocking density of 4–6 larvae L−1 in the indoor larval rearing and 3000 fry m−3 in outdoor hapa based nursery systems.

Temporal variations and pond age effect on plankton communities in semi-intensive freshwater marron (Cherax cainii, Austin and Ryan, 2002) earthen aquaculture ponds in Western Australia.

The abundance and diversity of the plankton community represents the health of the aquatic ecosystem, and plays an important role in the growth of cultured animals under aquaculture conditions. The temporal variations of plankton abundance, taxonomic composition, diversity, evenness and species richness were studied in three old and three new semi-intensive marron (Cherax cainii, Austin and Ryan, 2002) ponds. Water parameters such as temperature, dissolved oxygen, pH, turbidity, TAN, nitrite, nitrate and reactive phosphate were recorded, and plankton samples were collected every two months, for one year of juvenile production cycle. A total of twenty-six phytoplankton and seven zooplankton genera were recorded. Chlorophyceae was the dominant class of phytoplankton throughout the year, followed by Trebouxiophyceae. Rotifera comprised 49.8% of the total zooplankton community (individuals L−1), the largest proportion of any group. Temporal variations impacted the plankton abundance and community structure, and plankton abundance were more abundant during summer. The pond age did not influence the phytoplankton abundance, whereas zooplankton abundance was higher in older ponds.

Effect of hormonal stimulation on captive broodstock maturation, induced breeding and spawning performance of striped snakehead, Channa striata (Bloch, 1793)

In the present study, there was assessment of effects of gonadotropin treatments on broodstock maturation, induced breeding, and spawning outcomes of striped snakehead in captivity. The striped snakehead (n = 128) were equally distributed in four concrete tanks (15 m2) and hormone implants (500 IU human chorionic gonadotropin (hCG)/kg body weight) were inserted intramuscularly and striped snakehead broodstock administered this treatment were confined in two tanks and striped snakehead of a non-implanted group were confined in two tanks. The hormone implanted striped snakehead had a greater (P < 0.05) gonadosomatic index (GSI) and oocyte diameter in comparison to non-implanted striped snakehead. In a subsequent experiment, hCG and carp pituitary homogenate (CPH) were evaluated for inducing breeding. Dosages of hCG used were, 2,000 (TH1), 3000 (TH2), and 4000 (TH3) IU hCG/kg body weight of females. Dosages of CPH were, 20 (TP1), 30 (TP2), and 40 (TP3) mg CPH/kg body weight of females. Males were administered 0.75 of the dosage administered to females. The values for reproductive variables were estimated. Fertilization (89.0 ± 3.0 %) and hatching (92.0 ± 1.0 %) rates were greater (P < 0.05) in the TH1 group of implanted striped snakehead. Relative fecundity (19,023 ± 2211), as well as fertilization (96.2 ± 2.4 %), and hatching (96.6 ± 1.7 %) rates were greater in the TP2 group of the implanted striped snakehead. The results from the present study indicate broodstock treated with gonadotropins had greater spawning outcomes which might facilitate mass scale breeding and fertilized egg as well as juvenile production of striped snakehead in captivity.

Integrated production of Nile tilapia juveniles and lettuce using biofloc technology

The aim of the present study was to evaluate the use of the technology we have named for the first time as FLOCponics (biofloc + hydroponic) (FP) and conventional aquaponics (AP) systems in producing Nile tilapia (Oreochromis niloticus) juveniles and lettuce (Lactuca sativa). The experiment was carried out for 46 days and consisted of two cycles of lettuce production (23 days each) and one cycle of juvenile production. The physical–chemical variables of the water, zootechnical performance of the fish, growth performance and visual characteristics of the plants, nutrient dynamics, and characterization of the planktonic community were evaluated in both systems. The results showed better fish productive performance in FP, with a mean final weight of 36.7 g compared with 34.9 g in AP. For plants, the Cycle 2 in the AP system showed the best plant growth and visual results (98% of the plants received the highest scores—grades A (excellent) and B (good)—on the plant quality index), whereas in FP only 37% achieved these grades in the same cycle. The results suggest that the integrated production of tilapia juveniles and lettuce using FP might be technically feasible if specific fertilization management or mechanisms are developed to refine the critical points of the system (e.g., nutrient imbalance and solids accumulation in the plant roots) to improve plant production.

In vivo production of entomopathogenic nematodes suppressed by asymptomatic bacterial contaminants

Summary Entomopathogenic nematodes (EPN) are excellent biological control agents possessing recycling ability as one of their major attributes. We report the presence of asymptomatic bacteria that can lead to disrupted or low progeny production in Heterorhabditis indica. In a one-to-one in vitro competitive bioassay with contaminants associated with H. indica cuticle, there was a significant suppression in the growth of Sphingomonas koreensis when stressed with the nematode symbiont Photorhabdus luminescens; however, P. luminescens was suppressed when sandwiched between Ochrobactrum anthropi. Bacillus bombysepticus associated with laboratory-reared Galleria when stressed by P. luminescens was significantly suppressed, but not so in the reverse assay. Both O. anthropi and B. bombysepticus were found to be insecticidal to Galleria larvae when fed orally. Tripartite interactive studies on the growth and multiplication of H. indica-P. luminescens symbionts in Galleria larvae, predisposed to S. koreensis, revealed no significant difference initially in the hermaphrodite formation, but subsequently there was a significant decline in the formation of amphimictic females and the final production of infective juveniles. In in vitro studies, none of the contaminants supported the growth and development of axenic H. indica. Adequate precautions should be taken to maintain proper hygiene to eliminate such contaminants while culturing the Galleria and EPN for use in the biological control of insects.

The influence of organic carbon on the toxicity of sediment-associated dinonylnaphthalene sulfonic acids to the benthic invertebrates Tubifex tubifex and Hyalella azteca

Naphthalene sulfonic acids (NSAs) are used extensively in industrial applications as dispersants in dyes, rubbers, and pesticides, and as anti-corrosive agents in coatings, gels, and sealants. This study examined the toxicity of three NSA congeners, barium dinonylnaphthalene sulfonate (BaDNS), calcium dinonylnaphthalene sulfonate (CaDNS), and dinonylnaphthalene disulfonic acid (DNDS), to two benthic species, Tubifex tubifex and Hyalella azteca. Two substrates with different levels of organic carbon (sediment [2%] and sand [0%]) were used in toxicity tests. Juvenile production was the most sensitive endpoint for T. tubifex: the 28-d EC50s were <18.2, 22.2, and 64.0 μg/g dw in sand and 281.3, 361.6, and 218.9 μg/g dw in sediment for BaDNS, CaDNS, and DNDS, respectively. The 28-d LC50s for H. azteca were similar among compounds: 115.3, 82.1, and 49.0 μg/g dry weight (dw) in sand, and 627.3, 757.9, and >188.5 μg/g dw in sediment, for BaDNS, CaDNS, and DNDS, respectively. However, when LC50s were estimated based on concentrations of NSAs measured in overlying water (which can be an important route of exposure for H. azteca), BaDNS and CaDNS were 3–4 orders of magnitude more toxic than DNDS. The NSAs examined were >3-fold more toxic when present in substrates with no organic carbon (e.g., sand) for all H. azteca endpoints where LC/EC50s could be calculated and for sublethal endpoints for T. tubifex. The organic carbon content of the sediment appears to have acted as a sink and reduced NSA toxicity by decreasing bioavailability. Environmental sediment samples were collected from 12 river sites across southern Ontario. The maximum concentration of CaDNS observed in sediment collected from this region was 2.8 μg/g dw in sediment with 2% organic carbon; 100-fold lower than the lowest EC10 in the current study.

Single and combined toxicity of the pesticides abamectin and difenoconazole on soil microbial activity and Enchytraeus crypticus population

Besides being toxic to enchytraeids, pesticides may also affect microbial communities, which are the main diet of enchytraeids. This study aimed to analyze the individual and combined effects of the insecticide Kraft® 36 EC (abamectin) and the fungicide Score® 250 EC (difenoconazole) to soil microbial communities and Enchytraeus crypticus populations. The abamectin and difenoconazole effects to the microbial community metabolism, as revealed by qCO2 increase in the first two periods of exposure, might indicate an acute effect of pesticides, which might result in lowered microbial biomass once microorganisms spend more energy in detoxification processes than in microbial growth. E. crypticus juvenile production was not affected at the different conditions tested. However, the importance of microorganisms on the enchytraeids diet was ratified. Besides, it is important to emphasize that only one recommended dose of the pesticides was tested in this study. Hence, other situations (e.g. pesticides over application or a slower process of pesticides degradation) may result in a different scenario of effects and should be further investigated.