Juvenile Production Research Articles

The heterologous expression of a soybean (Glycine max) xyloglucan endotransglycosylase/hydrolase (XTH) in cotton (Gossypium hirsutum) suppresses parasitism by the root knot nematode Meloidogyne incognita.

A Glycine max (soybean) hemicellulose modifying gene, xyloglucan endotransglycoslase/hydrolase (XTH43), has been identified as being expressed within a nurse cell known as a syncytium developing within the soybean root undergoing the process of defense to infection by the parasitic nematode, Heterodera glycines. The highly effective nature of XTH43 overexpression in suppressing H. glycines parasitism in soybean has led to experiments examining whether the heterologous expression of XTH43 in Gossypium hirsutum (upland cotton) could impair the parasitism of Meloidogyne incognita, that form a different type of nurse cell called a giant cell that is enclosed within a swollen root structure called a gall. The heterologous transgenic expression of XTH43 in cotton resulted in an 18% decrease in the number of galls, 70% decrease in egg masses, 64% decrease in egg production and a 97% decrease in second stage juvenile (J2) production as compared to transgenic controls. The heterologous XTH43 expression does not significantly affect root mass. The results demonstrate XTH43 expression functions effectively in impairing the development of M. incognita at numerous life cycle stages occurring within the cotton root. The experiments reveal that there are highly conserved aspects of the defense response of G. max that can function effectively in G. hirsutum to impair M. incognita having a different method of parasitism.

General Status and Growth Potential of Fisheries Sector in Northern Cyprus

The island of Cyprus is a growing region in terms of the aquaculture sector. Northern Cyprus, in particular, is very weak for the aquaculture, although its environmental conditions are very favorable for aquaculture. While the number of fishers in Northern Cyprus was around 30-40 before 1974, the number of registered fishers has reached 1167 today. There are two existing cage facilities in the region, and there are no juvenile production facilities and feed mills. The amount of fish obtained from the natural stock with the fisheries activities are also limited. However, the amount of fish produced by aquaculture has been increasing since 2015 and today exceeds the amount of fish obtained from natural stock. The effect of the tourism sector on the increase in aquaculture and fish production is remarkable. In the country, for per capita meat consumption, fish product consumption ranks fourth. To increase the amount of fish consumed, a couple of suggestions made. This review has the most up to date data about fisheries and aquaculture sector for North Cyprus.

Consequences of surface coatings and soil ageing on the toxicity of cadmium telluride quantum dots to the earthworm Eisenia fetida.

The bioaccumulation potential and toxic effects of engineered nanomaterials (ENMs) to earthworms are poorly understood. Two studies were conducted following OECD TG 222 on Eisenia fetida to assess the effects of CdTe QDs with different coatings and soil ageing respectively. Earthworms were exposed to carboxylate (COOH), ammonium (NH4+), or polyethylene glycol (PEG) coated CdTe QDs, or a micron scale (bulk) CdTe material, at nominal concentrations of 50, 500 and 2000 mg CdTe QD kg-1 dry weight (dw) for 28 days in Lufa 2.2 soil. In the fresh soil study, earthworms accumulated similar amounts of Cd and Te in the CdTe-bulk exposures, while the accumulation of Cd was higher than Te during the exposures to CdTe QDs. However, neither the total Cd, nor Te concentrations in the earthworms, were easily explained by the extractable metal fractions in the soil or particle dissolution. There were no effects on survival, but some retardation of growth was observed at the higher doses. Inhibition of Na+/K+-ATPase activity with disturbances to tissue electrolytes, as well as tissue Cu and Mn were observed, but without depletion of total glutathione in the fresh soil experiment. Additionally, juvenile production was the most sensitive endpoint, with estimated nominal EC50 of values >2000, 108, 65, 96 mg CdTe kg-1 for bulk, PEG-, COOH- and NH4+-coated CdTe QDs, respectively. In the aged soil study, the accumulation of Cd and Te was higher than in the fresh soil study in all CdTe QD exposures. Survival of the adult worms was reduced in the top CdTe-COOH and -NH4+ QD exposures by 55 ± 5 and 60 ± 25%, respectively; and with decreases in growth. The nominal EC50 values for juvenile production in the aged soil were 165, 88, 78 and 63 mg CdTe kg-1 for bulk, PEG-, COOH- and NH4+-coated CdTe QDs, respectively. In conclusion, exposure to nanoscale CdTe QDs, regardless of coating, caused more severe toxic effects that the CdTe bulk material and the toxicity increased after soil ageing. There were some coating-mediated effects, likely due to differences in the metal content and behaviour of the materials.

Restored river habitat provides a natural spawning area for a critically endangered landlocked Atlantic salmon population.

Supplementing endangered fish populations with captive bred individuals is a common practice in conservation management. The aim of supplementary releases from hatchery broodstocks is to maintain the viability of populations by maintaining their genetic diversity. Landlocked Lake Saimaa salmon (Salmo salar m. sebago) has been critically endangered for the past half-century. As a result of anthropogenic disturbance, especially construction of hydroelectric power plants, the Lake Saimaa salmon has become completely dependent on hatchery broodstock. Recently, habitat restoration has been done in one of the former spawning rivers with the aim of creating a new natural spawning ground for the critically endangered population. Hatchery fish releases have also been revised so that in addition to juveniles, adult fish from the hatchery and from the wild have been released into the restored river. We assessed here if a restored river stretch can be used as a natural spawning ground and juvenile production area with the aim of improving genetic diversity of the critically endangered Lake Saimaa salmon. By constructing a pedigree of the released adults, and juveniles sampled from the restored river, we found that the majority of the released adults had produced offspring in the river. We also found that wild-caught spawners that were released into the restored river had much higher reproductive success than hatchery-reared parents that were released into the restored river at the same time. We found no significant differences in genetic diversity between the parent and offspring generations. Meanwhile, relatedness among different groups of adults and juveniles varied a lot. For example, while the hatchery-reared females were on average half-siblings, wild-caught females showed no significant relatedness. This highlights the importance of using pedigree information in planning the conservation and management of endangered populations, especially when artificial propagation is involved.

Improving pikeperch larviculture by combining environmental, feeding and populational factors

Pikeperch (Sander lucioperca) has a high potential for inland aquaculture diversification in Europe. Bottlenecks (i.e. low survival, cannibalism and deformity rates) hamper further expansion of pikeperch culture, because of the weak production performances at the nursery level. To improve the production of pikeperch juveniles under recirculation system we used a pilot scale larval rearing system (700 L tanks) and multifactorial designs. Three successive larval rearing trials (duration: 35-49 days) were conducted to identify the best combination of environmental, feeding and population factors. Considering the main significant effects observed on survival, growth, swim bladder inflation rates and biomass gain, a favourable combination of twelve factor (F) modalities was proposed (F1- initial density: 100 larvae.L-1, F2- no sorting of fish jumper, F3- no sibling population, F4- eggs from large females, F5- discontinuous feeding, F6- no co-feeding, F7- light intensity: 50 lx, F8- beginning of the weaning at 16 dph (days post-hatching), F9- weaning duration: 9 days, F10- water renewal rate of 100 % per hour, F11- tank cleaning during morning and F12- tank bottom-up water current). A final validation step was realized over a last trial (seven replicates, duration: 49 days), and validated with the best productive results obtained over the global experimental period (2015-2018). These results were: a final body weight of 815.64 ± 95.34 mg, a survival rate of 16.9 ± 1.7 %, a specific growth rate of 15.1 ± 5.9 %.d-1, a final fish biomass of 9.55 ± 0.23 kg, a swim bladder inflation rate of 92.6 ± 3.2 % and a food conversion rate of 0.65 ± 0.02 (dry food). The final stocking density was 13.6 kg.m-3 of rearing volume. Authors were able to validate and provide a reliable basic protocol for pikeperch larval rearing using recirculating units.

Effect of crossbreeding three divergent populations on the juvenile production and rearing performance of the redclaw crayfish Cherax quadricarinatus

Cherax quadricarinatus populations from different regions in Mexico have been exposed to varying environmental conditions and farming practices resulting in genetic drift. These populations have lost genetic variability due to selection pressure and inbreeding which could decrease reproductive capacity and growth rates. Three divergent groups from Baja California Sur (C), Tamaulipas (T) and Michoacan (M) were crossbred to evaluate the effect on reproduction and production of juveniles. There were no statistical differences in absolute fecundity and number of juveniles between the crosses. However, reference (two origin) and nucleus (three origin) crosses show that fecundity was at the higher end when the M breeder was male. Juvenile weight 45 days post-hatch for reference crosses had a smaller overall mean compared to parental or nucleus crosses. The nucleus crosses CT:M and TC:M showed positive heterosis for fecundity and produced juveniles, when compared to the best-performing parental group (C). After 195 days of rearing, juvenile mean growth for C and T offspring was 2.66 and 1.74 g higher than for M offspring. Reference crosses showed that, when the M breeder is female, body weight and growth rate are at the lower end of the overall range. This may relate to previous selective pressure for growth for the C and T populations. Reference crosses showed that juveniles from female M breeders (M:C, M:T) resulted in mean final weights statistically smaller when compared to the parental C group. Growth heterosis was positive for the nucleus when compared to parental M. A significant positive correlation was found between growth rate and Na (p = .002). A larger gene pool appears to improve adaptation to intensive rearing. Crossbreeding enhanced commercially important traits with the nucleus having similar performance when compared to parental C, while improving observed heterozygosity. The nucleus is suitable to commence a genetic selection program.

English

Abstract The Australian Redclaw crayfish, Cherax quadricarinatus, has been the subject of aquaculture development for more than 3 decades. Farm production from Australia and from around the world for this species has been relatively low, as suitable production technology continues to develop. The production of redclaw juveniles for the purpose of stocking to ponds for on-growing to marketable size, has been a particular constraint and new approaches to breeding and mass production of craylings have provided renewed impetus to industry expansion. This paper reviews the literature concerning redclaw juvenile production and provides a status report of current practices and innovations that may support further expansion of redclaw aquaculture.

Stability in reproductive timing and habitat usage of Chinook salmon across six years of varying environmental conditions and abundance

AbstractThe spatial and temporal distribution of spawning activity by autumn‐run Chinook salmon Oncorhynchus tshawytscha (Walbaum) was examined across multiple years. The study period included two years of extreme drought conditions when water temperatures in the spawning reach of the Stanislaus River were considered sub‐optimal for spawning and egg incubation. Despite varying levels of superimposition, redd counts and densities remained stable and positively associated with river location, indicating that superimposition may be driven by habitat preference rather than the absence of suitable spawning locations. Spawning occurred slightly later during drought years (6–10 days later compared with wetter years). This delay was attributable to deferred migration instead of deferred spawning, and the majority of redds were constructed at water temperatures exceeding the optimal temperature range. As a consequence, estimates of juvenile production during 2014 and 2015 were among the lowest on record. These findings may be related in part to the high hatchery contribution to the population, above‐average temperatures during spawning and incubation, and superimposition rates. Management recommendations include adequate cold‐water storage in the upstream reservoir, refined spawning habitat restoration techniques in the light of superimposition rates and, on a broader system scale, actions that reduce the amount of stray hatchery Chinook salmon.

Neuroestrogen synthesis modifies neural representations of learned song without altering vocal imitation in developing songbirds

Birdsong learning, like human speech, depends on the early memorization of auditory models, yet how initial auditory experiences are formed and consolidated is unclear. In songbirds, a putative cortical locus is the caudomedial nidopallium (NCM), and one mechanism to facilitate auditory consolidation is 17β-estradiol (E2), which is associated with human speech-language development, and is abundant in both NCM and human temporal cortex. Circulating and NCM E2 levels are dynamic during learning, suggesting E2’s involvement in encoding recent auditory experiences. Therefore, we tested this hypothesis in juvenile male songbirds using a comprehensive assessment of neuroanatomy, behavior, and neurophysiology. First, we found that brain aromatase expression, and thus the capacity to synthesize neuroestrogens, remains high in the auditory cortex throughout development. Further, while systemic estrogen synthesis blockade suppressed juvenile song production, neither systemic nor unilateral E2 synthesis inhibition in NCM disrupted eventual song imitation. Surprisingly, early life neuroestrogen synthesis blockade in NCM enhanced the neural representations of both the birds’ own song and the tutor song in NCM and a downstream sensorimotor region, HVC, respectively. Taken together, these findings indicate that E2 plays a multifaceted role during development, and that, contrary to prediction, tutor song memorization is unimpaired by unilateral estrogen synthesis blockade in the auditory cortex.

Egg diameter as a predictor for egg quality of California yellowtail (Seriola dorsalis)

The lack of knowledge in what optimizes egg and larval quality is an important limiting factor in developing culture techniques for any species. Inconsistent or poor egg quality significantly affects the production of larval and juvenile fish. Egg quality is a known predictor of subsequent larval viability, quality, and stress resistance. Without high quality eggs, it is not possible to optimize husbandry practices. Here we tracked egg quality in a population of California yellowtail (Seriola dorsalis), CYT. We used spawn events from three consecutive years and monitored basic egg quality metrics such as: spawn viability, egg diameter, oil diameter, hatch rates, larval size at hatch, and larval survival to first feeding. Along with these metrics we also ran proximate composition and fatty acid analysis of these spawn events on the viable portion of the eggs collected.During this study we demonstrated that egg diameters for S. dorsalis decreased as the spawning season progressed and water temperature increased. We showed that larger eggs lead to higher quality hatched larvae, and that using eggs earlier in the season would lead to better overall larval and juvenile production. Our fatty acid analyses suggest that both arachidonic acid (ARA) and linoleic acid (LA) were limiting fatty acids in eggs produced, and there is potential to improve the quality of cultured CYT eggs with the addition of these fatty acids to the broodstock diet.

Evaluation of biofloc generation protocols to adopt high density nursery rearing of Penaeus vannamei for better growth performances, protective responses and immuno modulation in biofloc based technology

Biofloc (BFT) based nursery rearing system help provides an additional food source, healthy juvenile production with better survival and an avenue for nitrogen removal through eco-friendly approach. It should be cost and energy efficient with a quick turn over. However, many questions remain unanswered regarding mechanisms of action and induced antibacterial/antiviral immune responses in penaeid shrimp especially during nursery phase. The present experiment was designed to evaluate the effects of biofloc treatments generated and maintained through three approaches on growth performances, physico-chemical parameters, microbial dynamics, feed utilization and immunological assessments in P. vannamei nursery rearing. The experiment was conducted in 500 L FRP tanks stocked with PL-III stage of Pacific white shrimp for 30 days at a stocking density of 6000 nos/m3. The heterotrophic bacteria level of 1 × 107 CFU/ml was maintained through three approaches differing in their generation; 1) biofloc lyophilized powder (BFP), 2) biofloc matured water (BFW) and 3) biofloc consortium (BFC) and compared with that of the conventional nursery rearing without biofloc treatment (Control). BFT treatments showed significantly higher growth as observed in average body weight (ABW) (BFP - 0.357 g, BFW - 0.363 g & BFC - 0.391 g) compared to control (0.188 g). BFT groups showed significantly (P < 0.01) higher survival (BFP (81.47%), BFW (79.73%), and BFC (85.4%)), than control groups. The population of heterotrophic bacteria was significantly (P < 0.05) increased in treatments when compared to control. But higher Vibrio load was recorded in the control than BFT water samples. BFT based nursery rearing system improves the water quality parameters when compared to the control. The cumulative mortality rate of biofloc reared juveniles was significantly lowered when challenged with Vibrio whereas, in control, it was higher. Further, certain immune genes like the prophenoloxidase, crustin, MAS, serine protease, alpha-2-M, antiviral genes, and RAN were up-regulated in the BFT groups. All these findings indicate that BFT nursery rearing system gives optimal and better culture condition displaying better survival, growth, disease tolerance, immune activity during the nursery phase and can be managed with minimal water exchange and maximum biosecurity.

Uptake, toxicity, and maternal transfer of cadmium in the oribatid soil mite, Oppia nitens: Implication in the risk assessment of cadmium to soil invertebrates

Cadmium (Cd) is a heavy metal of concern in contaminated sites because of its high toxicity to soil biota and humans. Typically, Cd exposure is thought to be dominated by dissolved Cd in soil pore water and, thus, dermal uptake. In this study, we investigated the uptake, toxicity, and maternal transfer of Cd in a standard soil invertebrate, the oribatid mite (Oppia nitens), which is common to boreal and temperate ecozones. We found total soil Cd predicted Cd uptake in adult and juvenile O. nitens with no significant uptake from pore water by juvenile mites. Cadmium significantly inhibited juvenile production and recruitment as well as reduced adult fecundity. Adult O. nitens maternally transferred 39–52% of their Cd body burden to juveniles (tritonymphs) while the maternally-acquired Cd accounted for 41% of the juvenile internal Cd load. Our results suggest that dermal adsorption of metal ions is not important for O. nitens and that maternal transfer of Cd in soil invertebrates has ecological and toxicological implications for populations of soil invertebrates. Maternal transfer should be incorporated as a criterion in setting environmental soil quality guidelines (SQGE) for cadmium and other non-essential heavy metals.

Density‐Dependent Effects of Invasive Red Swamp Crayfish Procambarus clarkii on Experimental Populations of the Amargosa Pupfish

AbstractThe adverse effects of invasive species are expected to be proportional to their relative densities. However, interference competition among conspecifics when invasive species are at high densities could limit such effects. These alternative hypotheses inspired us to test the density‐specific effects of red swamp crayfish Procambarus clarkii on experimental populations of the Amargosa Pupfish Cyprinodon nevadensis amargosae. The presence of crayfish had a significant influence on the survival of adult pupfish. In allopatry, adult pupfish survival was nearly 100%. However, the presence of crayfish resulted in significantly lower survival rates for adult pupfish, 84% and 69% survival for the low‐ and high‐density crayfish treatments, respectively. Crayfish also significantly affected the production of juvenile pupfish, with high juvenile production in the allopatric (705 juveniles/mesocosm) and low‐density crayfish treatments (705 juveniles/mesocosm). Juvenile production in both of these groups was significantly higher than that in the groups sympatric with high‐density crayfish (271 juveniles/mesocosm). The same pattern was observed when we evaluated the number of juvenile pupfish that were produced per adult female. We tested the hypothesis that interference competition among the crayfish would decrease predator efficacy by comparing the high‐density crayfish treatment with a fourth high‐density crayfish treatment wherein the crayfish were tethered. There was no significant difference in the rate of adult survivorship of the Amargosa Pupfish in the tethered and untethered high‐density treatment groups (70% and 69%, respectively). However, tethering resulted in a significant increase in juvenile production in the high‐density crayfish treatments (493 and 271 juveniles per mesocosm were produced in the tethered and untethered groups, respectively). The same patterns were observed when we examined the number of juvenile pupfish that was produced per adult female. These findings are inconsistent with the interference competition hypothesis, while supporting the hypothesis of density‐dependent effects of crayfish on Amargosa Pupfish populations. These findings suggest that reducing crayfish density will be a beneficial management tool for reducing the effects of crayfish on benthic fish populations.

A reconsideration of the safety of fenoxycarb (IGR) in soil environment: The toxicity of fenoxycarb to Yuukianura szeptyckii (Collembola)

Abstract Fenoxycarb, a juvenile hormone agonist has been widely used to control various insect pests in agriculture. Fenoxycarb has been considered environmentally safe because it degrades quickly and has lower mammalian toxicity compared with many conventional pesticides. To date, fenoxycarb is reported safe for soil organisms, but this conclusion is based solely on toxicity studies with Folsomia candida (Collembola) and Eisenia fetida (earthworm). The aim of this study was to investigate the toxic effect of fenoxycarb on Yuukianura szeptyckii (Collembola) to assess further whether this chemical is environmentally safe or not. After 28 d of exposure of fenoxycarb in the soil, adult survival and juvenile production were assessed. The median lethal concentration (LC50) value for adult was 955.2 mg/kg and the median effective concentration (EC50) and no observed effect concentration (NOEC) value for juvenile production was 0.2 mg/kg and

Predicting recruitment density dependence and intrinsic growth rate for all fishes worldwide using a data‐integrated life‐history model

AbstractFisheries scientists use biological models to determine sustainable fishing rates and forecast future dynamics. These models require both life‐history parameters (mortality, maturity, growth) and stock‐recruit parameters (juvenile production). However, there has been little research to simultaneously predict life‐history and stock‐recruit parameters. I develop the first data‐integrated life‐history model, which extends a simple model of evolutionary dynamics to field measurements of life‐history parameters as well as historical records of spawning output and subsequent recruitment. This evolutionary model predicts recruitment productivity (steepness) and variability (variance and autocorrelation in recruitment deviations) as well as mortality, maturity, growth, and size, and uses these to predict intrinsic growth rate (r) for all described fishes. The model confirms previous analysis showing little correlation between steepness and either natural mortality or asymptotic maximum size (). However, it does reveal taxonomic patterns, where family Sebastidae has lower steepness () and Salmonidae has elevated steepness () relative to the prediction for bony fishes (class Actinopterygii, ). Similarly, genus Sebastes has growth rate (0.09) approaching that of several shark families (Lamniformes: 0.02; Carcharhiniformes: 0.02). A cross‐validation experiment confirms that the model is accurate, explains a substantial portion of variance (32%–67%), but generates standard errors that are somewhat too small. Predictive intervals are tighter for species than for higher‐level organizations (e.g. families), and predictions (including intervals) are available for all fishes worldwide in R package FishLife. I conclude by outlining how multivariate predictions of life‐history and stock‐recruit parameters could be useful for stock assessment, decision theory, ensemble modelling and strategic management.

Restoration-mediated secondary contact leads to introgression of alewife ecotypes separated by a colonial-era dam.

Secondary contact may have important implications for ecological and evolutionary processes; however, few studies have tracked the outcomes of secondary contact from its onset in natural ecosystems. We evaluated an anadromous alewife (Alosa pseudoharengus ) reintroduction project in Rogers Lake (Connecticut, USA), which contains a landlocked alewife population that was isolated as a result of colonial‐era damming. After access to the ocean was restored, adult anadromous alewife were stocked into the lake. We assessed anadromous juvenile production, the magnitude and direction of introgression, and the potential for competition between ecotypes. We obtained fin clips from all adult alewife stocked into the lake during the restoration and a sample of juveniles produced in the lake two years after the stocking began. We assessed the ancestry of juveniles using categorical assignment and pedigree reconstruction with newly developed microhaplotype genetic markers. Anadromous alewives successfully spawned in the lake and hybridized with the landlocked population. Parentage assignments revealed that male and female anadromous fish contributed equally to juvenile F1 hybrids. The presence of landlocked backcrosses shows that some hybrids were produced within the first two years of secondary contact, matured in the lake, and reproduced. Therefore, introgression appears directional, from anadromous into landlocked, in the lake environment. Differences in estimated abundance of juveniles of different ecotypes in different habitats were also detected, which may reduce competition between ecotypes as the restoration continues. Our results illustrate the utility of restoration projects to study the outcomes of secondary contact in real ecosystems.

Optimization of techniques and procedures for the production and management of live feed used in the larval culture of the freshwater shrimp Cryphiops caementarius (Decapoda: Palaemonidae)

The variation in saline requirements during larval development of Cryphiops caementarius establishes a particular coexistence in the culture systems between the shrimp larvae, the microalgae and Artemia nauplii. Although the technology for the mass production of freshwater prawn juveniles has advanced positively, the non-commercial availability of an exclusive live feed for amphidromous crustaceans, such as C. caementarius , has created the need to optimize the management of organisms commonly used as feed in the larval culture of marine crustaceans. We investigated the effect of salinity on embryonic development dynamics and the hatching rate of commercial Artemia sp. cysts, including the effect of cooling decapsulated cysts on the hatching rate, and the effect of salinity on the behavior of marine microalgae used as live feed in the larviculture of C. caementarius . The results encourage a sustained and stable production of Artemia nauplii at different salinities, and at the same time, reduce by 80% the daily time used in feeding activities. Also, the information generated in this study adds critical information about activities and procedures for the larviculture of the northern river shrimp, which could be used to improve larval feeding strategies either in C. caementarius or in other amphidromous crustacean species.

The Lanzarote Population of the African Houbara Chlamydotis undulata fuertaventurae: Census, Sex Ratio, Productivity, and a Proposed New Survey Method

Lanzarote island, in the Canary archipelago, is the main stronghold of the Canarian subspecies of the African Houbara Bustard Chlamydotis undulata fuertaventurae. The size of this population has been estimated several times in recent decades, based on extrapolations of bird densities obtained in small sampling areas. Here we present the results of the first complete census of the Houbara population of this island, based on car transects combined with frequent and prolonged scanning stops, and carried out during the mating season, in January-February 2018. Based on a count of 370 birds (161 males, 209 females) we estimate a total population of 440-452 Houbara Bustards on the island. For the first time, a sex-ratio figure was obtained for this species: 1.41 females per male. The annual production of juveniles was recorded for three years and varied between 5.83 and 19.57 juveniles per hundred females. The census method used in this study is proposed as an alternative to the line transects used previously, since it avoids possible methodological flaws that probably overestimate the population. The present method also enables sex ratio and productivity to be determined, and it established the locations of most displaying males. These are important parameters for evaluating the conservation status and reproductive performance of this endangered subspecies of the African Houbara.—Alonso, J.C., Palacin, C. and Abril-Colon, I. (2020). The Lanzarote population of the African Houbara Chlamydotis undulata fuertaventurae: census, sex ratio, productivity, and a proposed new survey method. Ardeola, 67: XX-XX.

Excess zinc uptake in &lt;i&gt;Paronychiurus kimi&lt;/i&gt; (Collembola) induces toxic effects at the individual and population levels

The purpose of this study was to investigate the toxic effects of zinc in collembolan Paronychiurus kimi at the individual (survival and juvenile production) and population (population growth and age structure) levels after 28 days of exposure in artificially spiked soil. These toxic effects were interpreted in conjunction with the internal zinc concentrations in P. kimi. The EC50 value for juvenile production based on the total zinc concentration was 457 mg Zn kg-1 dry soil, while the LC50 value for adult survival and ri=0 value for population growth were within the same order of magnitude (2,623 and 1,637 mg Zn kg-1 dry soil, respectively). Significant differences in adult survival, juvenile production, and population growth compared with the control group were found at concentrations of 1,500, 375, and 375 mg Zn kg-1 dry or higher, respectively, whereas significant differences in the age structure, determined by the proportion of each age group in the population, were observed in all treatment groups. It appeared that the internal zinc level in P. kimi was regulated to some extent at soil zinc concentrations of ≤375 mg Zn kg-1 dry soil, but not at high soil zinc concentrations. These results indicate that, despite zinc being regulated by P. kimi, excess zinc exceeding the regulatory capacity of P. kimi can trigger changes in the responses at the individual and population levels. Given that population dynamics are affected not only by individual level but also by population level endpoints, it is concluded that the toxic effects of pollutants should be assessed at various levels.

PRODUCTION PERFORMANCE OF TAMBAQUI JUVENILES SUBJECTED TO SHORT FEED-DEPRIVATION AND REFEEDING CYCLES

This study proposes to investigate whether short restricted-feeding cycles during the pre-fattening phase of tambaqui (Colossoma macropomum) juveniles affect their production performance and yield in a semi intensive system and if this practice can be introduced as an alternative to reduce production costs in the pre-fattening phase of this species. The fish (8.07 ± 0.07 g) were subjected to short restricted-feeding periods under controlled laboratory conditions (experimental boxes) for 60 days (Phase I). Three feeding strategies were tested, namely: dairy feeding (Control); five days of feeding followed by two days of deprivation (5F/2D); and two days of feeding followed by four days of deprivation (2F/4D). Subsequently, the fish from each treatment (feeding regimes) evaluated in Phase 1 were transferred to an excavated pond with low water exchange and no supplemental aeration (semi-intensive system) where they were fed continuously for 65 days (Phase II). At the end of both phases, performance, metabolic and hematological parameters and the centesimal composition of the filets were analyzed and an economic assessment was undertaken based on the total operating cost (TOC) of production in the different feeding regimes. The restricted-feeding cycles 2F/4D and 5F/2D (Phase I) affected the performance of the fish, which showed lower daily weight gains and specific growth rates (SGR), resulting in lower viscerosomatic index (VSI) and morphometric measurements. However, apparent feed conversion did not differ across the treatments. The feed-deprived fish used triglycerides as an energy source, maintaining their blood glucose levels close to those of the continuously fed group (control). When they started to be feed daily for 65 days (Phase II), the metabolic (triglycerides) and hematological parameters (hematocrit and hemoglobin) equaled those of control group. Nevertheless, their final weight and morphometric measurements were lower than those of non-restricted feed, indicating a partial compensatory growth in tambaqui juveniles. Short restricted-feeding cycles applied in the pre fattening phase for 60 days negatively affected performance and led to metabolic and hematological alterations in tambaqui (Colossoma macropomum) juveniles. Although these short restricted-feeding cycles resulted in less expenditure on labor and feeding, the fish under those conditions did not develop equally to those fed daily, culminating in less biomass produced during the fattening period in a semi-intensive system for 65 days. Ultimately, this led to a higher total operating cost per gram of produced fish, demonstrating the economic infeasibility of this practice for tambaqui juvenile production.