Young Fish Research Articles

Toxic effects of naturally-aged microplastics on zebrafish juveniles: A more realistic approach to plastic pollution in freshwater ecosystems

We aim at evaluating the toxicity of naturally-aged polystyrene microplastics (MPs) in Danio rerio at intermediate development stage. Animal models were stactically exposed to 4 × 104 and 4 × 106 microparticles/m3 for five days – this concentration is environmentally relevant. We evaluated MP’s impact on animals’ nutritional status and REDOX balance, as well as its potential neuro- and cytotoxic action on them. Initially, MPs did not induce any change in total carbohydrates, triglycerides and total cholesterol levels. MP accumulation was associated with oxidative stress induction, which was inferred by the nitrite and thiobarbituric acid reactive substances levels. Furthermore, we observed that such stress was not counterbalanced by increase in the assessed enzymatic (total glutathione, catalase and superoxide dismutase) and non-enzymatic (total thiols, reduced glutathione and DPPH radical scavenging activity) antioxidants. The association between high acetylcholinesterase activity and numerical changes in neuroblasts distributed on animals' body surface confirmed MP’s neurotoxic potential. MP’s ability to induce apoptosis and necrosis processes in animals' erythrocytes suggested its cytotoxic action; therefore, the present study is pioneer in providing insight on how MPs can affect young freshwater fish at environmental concentrations. It is essential knowing the magnitude of these pollutants’ impact on the ichthyofauna.

The core circadian component, Bmal1, is maintained in the pineal gland of old killifish brain.

SummaryCircadian rhythm is altered during aging, although the underlying molecular mechanisms remain largely unknown. Here, we used the turquoise killifish as a short-lived vertebrate model to examine the effects of aging on the major circadian network comprising the four mammalian clock protein homologs, Bmal1, Clockb, Cry1b, and Per3, which are highly conserved in the killifish with 50%–85% amino acid sequence identity to their human counterparts. The amplitude of circadian rhythm was smaller in old fish (14 weeks) than in young fish (6 weeks). In old fish brain, the Bmal1 protein level was significantly downregulated. However, the Bmal1 interaction with Clockb and chromatin binding of Bmal1 to its downstream target promoters were retained. Furthermore, Bmal1 was relatively well maintained in the pineal gland compared with other regions of the old fish brain. The results suggest that the circadian clock system in the killifish becomes spatially confined to the pineal gland upon aging.

Juvenile fish assemblages in the Jinju Bay region, Korea

Assemblages of juvenile fish and associated abiotic parameters were investigated inside and outside Jinju Bay in southern Korea, on a monthly basis from December 2014 to November 2015. Fluctuations in water temperature and salinity were larger inside than outside the bay. In total, 534,657 individuals per square kilometre from 81 fish species and 47 families were collected during the study period. The most dominant species was Nuchequula nuchalis both inside (25.6%) and outside (26.9%) the bay. The next dominant species were Thryssa kammalensis (17.9%) and Zoarces gillii (16.0%) inside the bay and Liparis tanakae (16.9%) and T. kammalensis (9.0%) outside the bay. Forty species (33% of total number of individuals) of young fish were recorded inside the bay and 47 species (52%) outside the bay. Therefore, it appears that a diversity of fish use nursery grounds inside and outside Jinju Bay. In particular, the following six species appeared: Z. gillii, Pleuronichthys cornutus, L. tanakae, Hemitripterus villosus, Pennahia argentata, and Xenocephalus elongates. Due to assemblage differences for fishes within Jinju Bay and outside the bay, management of both areas is required to maintain current diversity of species in the region.

Development of Open-Field Behaviour in the Medaka, Oryzias latipes.

Simple SummaryAnimal models play an important role in research on behaviour and its impairment. Fish larvae allow researchers to conduct experiments on large samples in just a few days and with small-scale experimental infrastructure, substantially increasing research output. However, several aspects of larval biology, including their behaviour, are frequently unknown. Our study has demonstrated that the most important behavioural paradigm for studying anxiety and stress in animals, the open-field test, can be used in the larvae of an important fish genetic model, the medaka. This finding will allow researchers to develop models to study anxiety and stress disorders based on medaka larvae.The use of juvenile and larval fish models has been growing in importance for several fields. Accordingly, the evaluation of behavioural tests that can be applied to larvae and juveniles is becoming increasingly important. We tested medaka at four different ages (1, 10, 30, and 120 dph) in the open field test, one of the most commonly used behavioural assays, to investigate its suitability for larvae and juveniles of this species. We also explored ontogenetic variation in behaviour during this test. On average, adult 120-day-old medaka showed higher locomotor activity in terms of distance moved compared with younger fish. Our analysis suggests that this effect was derived from both quantitative changes in locomotion related to the ontogenetic increase in fish size as well as qualitative changes in two aspects of locomotor behaviour. Specifically, time spent moving was similar between 1- and 10-day-old medaka, but progressively increased with development. In addition, we revealed that adult medaka showed constant levels of activity, whereas younger medaka progressively reduced their activity over the course of the entire experiment. The thigmotaxis behaviour typically used to assess anxiety in the open field test emerged at 120 days post-hatching, even though a difference in the temporal pattern of spatial preference emerged earlier, between 10 and 30 days post-hatching. In conclusion, some measures of the open field test such as total distance moved allow behavioural phenotyping in the medaka of all ages, although with some degree of quantitative and qualitative developmental variation. In contrast, immature medaka appear not to exhibit thigmotactic behaviour.

Nitrogen and phosphorus dynamics in Nile tilapia farming in excavated rearing ponds

The purpose of this study was to determine the total nitrogen (TN) and total phosphorus (TP) balance during intensive tilapia farming in excavated ponds. To quantify TN and TP released into the environment, the supply water, effluents at the harvest time, fish composition, feed, and sediment were analysed. The mass balance between the amount of nutrients that is inserted through the feed, which is transformed into biomass by the fish and is retained in the sediment was calculated based on dry matter. The nutrient load arriving from the supply water was calculated as a function of the concentration of TN and TP. The TN and TP dynamics during the harvesting process in three different pond sizes identified that, on average, 2.37% of TN and 2.05% of TP inserted into the system during rearing is eliminated with 10.64% TN and 37.01% TP are retained in the sediment. The TN and TP input into the system occurs through the water supply, young fish, and the feed, the latter being responsible for about 92.87% TN and 96.05% TP. The feed composition indicates that the P level of the food is above the nutritional recommendations for the species. The amount of TP accumulated in the sediments indicates that there is a need for good management practices for water quality during the rearing and sediment management period before the beginning of a new production cycle.

Preparation and optimization of rapid and sensitive coagglutination test for detection of infectious pancreatic necrosis virus (IPNV)

The aim of this study is the development of a coagglutination test for rapid diagnosis of infectious pancreatic necrosis (IPN) virus which causes an acute infectious viral disease with high mortality in young salmonid fish. Serotypes Sp, Ab, WB of the IPNV were cultivated in BF-2 cells and purified by linear sucrose density gradient centrifugation. Hyperimmune sera against purified IPNV serotypes were collected from immunized guinea pigs. Coagglutination test conjugates were prepared by using sensitized S. aureus and hyperimmune sera. Cell culture derived salmonid pathogens such as infectious hematopoietic necrosis virus (IHNV), viral haemorrhagic septicaemia virus (VHSV) and epizootic hematopoietic necrosis virus (EHNV) were used to determine the specificity of the test as control. Upward comparison of the preferability for the rapid diagnosis was also carried out with ELISA and RT-PCR. The validation studies of newly developed coagglutination test were carried out in accordance with the Manual of Diagnostic Tests for Aquatic Animals. Consequently, determined detection limit of the test was approximately 105.25 TCID50/mL for the Sp and Ab serotypes and 107.75 TCID50/mL for the WB in laboratory conditions. The results indicated that newly developed coagglutination test was compatible with ELISA and RT-PCR in positive cell culture supernatants. It was concluded that this test would be an economic, rapid and reliable method for the diagnosis of IPN virus in cell culture.

Multiple life‐stage connectivity of Pacific halibut (Hippoglossus stenolepis) across the Bering Sea and Gulf of Alaska

AbstractPacific halibut (Hippoglossus stenolepis) is managed as a single stock throughout the Gulf of Alaska (GOA) and eastern Bering Sea (BS), but biogeographical barriers and the potential for differential impacts of climate change may alter habitat use and distributions, and restrict connectivity between these ecosystems. To improve our understanding of larval dispersal pathways and migrations of young fish within and between GOA and BS, we (a) examined potential pelagic larval dispersal and connectivity between the two basins using an individual‐based biophysical model (IBM) focusing on years with contrasting climatic conditions and (b) tracked movement of fish up to age‐6 years using annual age‐based distributions and a spatiotemporal modeling approach. IBM results suggest that the Aleutian Islands constrain connectivity between GOA and BS, but that large island passes serve as pathways between these ecosystems. The degree of connectivity between GOA and BS is influenced by spawning location such that an estimated 47%–58% of simulated larvae from the westernmost GOA spawning location arrived in the BS, with progressive reductions in connectivity from spawning grounds further east. From the results of spatial modeling of 2‐ to 6‐year‐old fish, we can infer ontogenetic migration from the inshore settlement areas of eastern BS toward Unimak Pass and GOA. The pattern of larval dispersal from GOA to BS, and subsequent post‐settlement migrations back from BS toward GOA, provides evidence of circular, multiple life stage, connectivity between these ecosystems, regardless of climatic variability or year‐class strength.

Life history plasticity affects the population structure and distribution of the widespread migratory fish Galaxias brevipinnis

Partial migration, or variation in migratory propensity within populations, has been reported across a range of taxa, including fish. Otolith microchemistry has revealed a high degree of life history plasticity in many amphidromous species, with diadromous and non-diadromous recruitment occurring. We examined this plasticity and its effect on population structure, dispersal and recruitment in Galaxias brevipinnis, an amphidromous fish widespread around New Zealand. We used otolith microchemistry analyses to examine recruitment sources and fish surveys to assess abundance and size structure in two large river systems, each containing naturally formed lakes and no obvious physical barriers to migration. Otolith analyses revealed discrete recruitment sources for stream-resident populations, with marine recruitment supporting populations downstream from lakes and exclusively lake-derived recruitment for populations upstream of lakes. Although diadromous G. brevipinnis were abundant within 10km of the sea, the abundance and relative proportion of younger fish declined as distance upstream increased, until a lake was reached, at which point abundance and the proportion of small individuals increased. The results provide a strong indication that supply is limiting recruitment for G. brevipinnis as distance from pelagic larval habitat increases, and that discrete recruitment sources and population structuring exist even within drainages.

Intestinal Explant Cultures from Gilthead Seabream (Sparus aurata, L.) Allowed the Determination of Mucosal Sensitivity to Bacterial Pathogens and the Impact of a Plant Protein Diet.

The interaction between diet and intestinal health has been widely discussed, although in vivo approaches have reported limitations. The intestine explant culture system developed provides an advantage since it reduces the number of experimental fish and increases the time of incubation compared to similar methods, becoming a valuable tool in the study of the interactions between pathogenic bacteria, rearing conditions, or dietary components and fish gut immune response. The objective of this study was to determine the influence of the total substitution of fish meal by plants on the immune intestinal status of seabream using an ex vivo bacterial challenge. For this aim, two growth stages of fish were assayed (12 g): phase I (90 days), up to 68 g, and phase II (305 days), up to 250 g. Additionally, in phase II, the effects of long term and short term exposure (15 days) to a plant protein (PP) diet were determined. PP diet altered the mucosal immune homeostasis, the younger fish being more sensitive, and the intestine from fish fed short-term plant diets showed a higher immune response than with long-term feeding. Vibrio alginolyticus (V. alginolyticus) triggered the highest immune and inflammatory response, while COX-2 expression was significantly induced by Photobacterium damselae subsp. Piscicida (P. damselae subsp. Piscicida), showing a positive high correlation between the pro-inflammatory genes encoding interleukin 1β (IL1-β), interleukin 6 (IL-6) and cyclooxygenase 2(COX-2).

Microanalysis of scale morphology in killifish, Aphaniops hormuzensis inhabiting ecologically diverse environments (Cyprinodontiformes; Aphaniidae)

Ecologically, Aphaniops hormuzensis populations occupying diverse environments in southern Iran and showed substantial morphological variation across its range. In this study, three different habitats were chosen and identified as group A (sulfur rich spring), group B (salty River), and group C (urban canal), and scale microstructures and scale shape was inspected among three groups. The SEM imaging indicated that lepidonts were more developed on the scale of larger (group C, SL > 30 mm) than younger fish (group A, SL < 30 mm). We tentatively concluded that lepidonts are formed during scale development so that in the earlier stages of fish development, scales probably do not have lepidont. Also, the size and shape of lepidonts vary between the populations, and their shape and orientation within a given species affected by the fish size rather than the local ecological conditions of habitats. The number of radii was relatively higher in group C (12.58 ± 0.66 in males and 13.00 ± 1.89 in females). Similar to what is mentioned before in the case of lepidont, the inter-population variation in the number of radii seems to be influenced by fish size. Group A (SL < 30 mm) had a relatively large focus diameter (0.14 ± 0.02 in males and 0.36 ± 0.44 in females). It is assumed that the focus size is large at the earlier stage of fish development, but later during the fish growth, and by increasing the scale size, the focus diameter is reduced. In conclusion and agreement with previous studies, scale surface morphology and microstructure could be employed to discriminate certain populations, while scale size and J-indices could not help in distinguishing the populations. It is also proposed that the characteristics of scale morphology in the population-level are influenced by the combination of genetic, and environmental factors, as well as fish development.

Spatiotemporal changes in demersal fish habitats suggest potential impacts of fishing pressure: A case study of yellow seabream Dentex hypselosomus in the East China Sea

We evaluated spatiotemporal dynamics of yellow seabream (YSB) in the East China Sea (ECS) from 1993 to 2018 with a delta-type approach using generalized additive models (delta-GAM). We used catch records from the Japanese bull-trawl fishery and otter-trawl surveys. The delta-GAMs incorporated several explanatory variables and predicted YSB habitats for each size category. The best models, based on the Bayesian information criterion, included all available explanatory variables: season, fishing method, temperature at 100-m depth, bottom depth and spatial and spatiotemporal effects. Temperature and bottom depth had different influences on the catch-per-unit-effort (CPUE) for each size category: there were positive effects for young fish across a wide range of temperatures and depths, whereas for adult fish the positive effects only appeared at colder temperatures and deep bottom depths. Habitat predictions showed high presence probabilities for young fish over a broader area than for adult fish through all periods. CPUEs declined for both sizes after the 2000s in the mid- to southern ECS (≤31∘N) but increased for adult fish in the north (≥31∘N). Previous studies reported that Chinese fisheries have drastically exploited fish stocks in the ECS after the 1980s and 1990s and the current fishing intensities in the mid- to southern ECS could indicate high levels, whereas Japanese vessels operated sparsely and only in the narrow area of northern region after the 2000s. These facts suggest that the different fishery exploitation rates in different locations could have significant influences on spatiotemporal patterns of YSB distributions in the ECS.

Sex and Age-related Parasitism of &lt;i&gt;Clarias gariepinus&lt;/i&gt; in earthen ponds in African Regional Aquaculture Centre, Aluu, Rivers State, Nigeria

This study aimed at investigating the sex and age-related parasitic burden of Clarias gariepinus cultured in earthen ponds. Eighty–five (85) fish samples were selected randomly for analyses from three earthen ponds. Sexing was done by the observation of the urinogenital papillae. For parasitological analysis, skin and gill scrapes were taken for external parasites while the stomach and intestines were slit open, rinsed and observed for helminthic worms. Parasites identified included; Chilodonella sp. (0.3%), Ichthyophthirius sp. (41.1%), Trichodina sp. (55%), Icthyobodo sp., (1.0%) and Gyrodactylus sp. (2.4%). From the study 31 out of 56 males and 20 out of 27 females were infected with parasites. Prevalence of infection in males and females were 55.36% and 74.07% respectively. Mean intensity of parasites was also higher for females (150.75) than for males (62.68) Chi square analysis however, revealed no significant effect (p&lt;0.05) of parasitism on gender. It was further observed that juvenile males and early adult females respectively, had more parasites with 55.3 and 92.4 parasite mean intensities. Among age groups, the mid juveniles (25-99g) (19%), late juveniles (100-299g) (65%) and early adults (300-500g) (14%) were most infected, although there was no significant effect (p&lt;0.05). Sex-related prevalence could be based on hormonal changes and reproduction in females, and competitive search for mates by males. Age-related infection was predicated upon active feeding habits reported among fish of these ages It is therefore recommended that routine health checks be carried out for pond cultured fish. Furthermore, that older fish be sorted and kept together, as they would have stronger immunity than younger fish.&#x0D; Keywords; Zoonoses, fish infection, late juveniles, earthen pond, Clarias gariepinus, sex, age

Shifting Trophic Control of Fishery–Ecosystem Dynamics Following Biological Invasions

Increasing human population size and mobility have accelerated the translocation of nonnative species globally, which has become a major threat to conservation of biodiversity and ecosystem services. Introduced species can disrupt species interactions of the recipient ecosystem, triggering system-wide events, and amplify or dampen effects of existing pressures. We show how two pervasive intercontinental invasive consumers in North American lakes, dreissenids (filter-feeding mussels) and Bythotrephes (carnivorous zooplankton), nonlinearly modify consumer-resource dynamics and undermine management interventions to rebuild cold-water predatory fish biomass. Synthesizing 30 yr (1986-2015) of lake-wide monitoring data with a dynamic mass-balance food-web model (consisting of 61 species and trophic groups), we reconstructed historical food-web dynamics of Lake Simcoe, a large, temperate lake in Ontario, Canada that has shifted from a turbid to clear-water state. We then analyzed patterns of biomass fluctuations of three recreationally harvested, ecologically connected populations; lake trout (Salvelinus namaycush, a piscivore), lake whitefish (Coregonus clupeaformis, a benthivore), and cisco (C. artedi, a planktivore) before and after the invasions by testing hypotheses on their delayed recoveries under management interventions-predator manipulations (fishery removal and stocking) and nutrient (phosphorus) load reduction. Analyses suggest that fishery harvest primarily regulated early recovery trajectories of the piscivore and planktivore, weakening top-down control prior to the establishment of the invasive consumers. By contrast, the benthivore biomass patterns were shaped, in part, by the invasive mussels (via diet shift), independently of management actions. Although improved water quality (with reduced hypoxia in deeper water) and, in turn, higher macrophyte production are projected to expand the predation refuge for young fish, intensified planktivory (by Bythotrephes) and herbivory (by dreissenids) have triggered shifts in community composition (from pelagic to demersal dominance). These system-wide shifts, in turn, have substantially diminished ecosystem productivity, thereby shrinking fishery yields. Novel consumers can rewire food webs, disrupt energy flows, and suppress predator recoveries, underscoring the need to account for altered ecological reality when sustainably managing fishery resources in invaded ecosystems.

Sex ratio and first maturity of blackeye thicklip wrasse Hemigymnus melapterus Bloch, 1791 in Spermonde Archipelago

Blackeye thicklip wrasse Hemigymnus melapterus is a Labridae that was widespread throughout the tropical and subtropical waters of Indo-Pacific. In eastern Indonesia, blackeye thicklip wrasse found from the Strait of Bali, Mentawai Islands, Raja Ampat Islands, Manado and surrounding areas, and Banggai; while in central Indonesia, blackeye thicklip wrasse found in the waters of the Spermonde Archipelago. This research aims to analyze the sex ratio, gonad maturity stage, and the size at first maturity of blackeye thicklip wrasse in the Spermonde Archipelago. This research was done on the population of blackeye thicklip wrasse in the Spermonde Archipelago, South Sulawesi, Indonesia. Samples were collected from fishermen caught landed in the Rajawali Makassar Fisheries Port at Makassar City. Blackeye thicklip wrasse sex ratio was not balanced. This imbalance was thought to have something to do with the “r” reproductive strategy where blackeye thicklip wrasse tries to produce as many eggs as possible to maintain its population. The success of this strategy probably supported by protogyny reproduction patterns where young fish can produce eggs as fast and as much as possible before being devoured by predators. Based on its gonad structure, blackeye thicklip wrasse could be classified as fish with a total spawning pattern that take place long spawning period or individual different spawning period throughout the year. The size at the first maturity of blackeye thicklip wrasse female was 21.4 cm; it was much smaller than half the size that has ever been caught.

The Water in Which We Are Swimming: Introduction to the Special Issue: Developing a Common Understanding of Networks of Care

A famous parable tells of two young fish swimming along. An older fish, swimming the other way, nods at them and says, “Good morning, boys. How’s the water?” The two young fish swim on for a bit, a...

Rate of sexual maturation and fecundity of the roach Rutilus rutilus (L.) of the Volga reach of the Rybinsk reservoir

Climate warming and the introduction of a new mass species of clam Dreissena bugensis can potentially lead to changes in the reproductive capacity of benthic fish species living in the upper Volga reservoirs. The age of puberty, the structure of the spawning stock, and fecundity are the main indicators of reproduction that determine, together with indicators such as the survival of young fish and the degree of fishing load, the relative number of species in the ichthyofauna. The purpose of this work was to study the size and age of the onset of puberty and the dynamics of fecundity of roach Rutilus rutilus in the Volga ples of the Rybinsk reservoir. Determination of individual absolute fecundity was performed by counting eggs in fresh gonads, without the use of fixation. The age of fish was determined by scales, and vertebrae and operculum were used as additional recording structures. As a result, it is shown that the beginning of sexual maturation of female roach occurs when reaching the age of 3+ and a length of more than 9 cm. Late maturing females were 4+ years old and over 18 cm long. The beginning of sexual maturation of males could not be determined. The smallest males in the catches, 7–8 cm long, were all sexually Mature. The maximum age of fish reached 12+ years with a length of no more than 32 cm. Individual absolute fertility ranged from 1,75 to 178,46 thousand eggs. The value of relative fertility ranged from 79 to 308, with an average of 171 eggs/g. The result concluded that high absolute and relative fecundity of roach and dynamic changes of fertility in terms of increase in average water temperature and absolute improvement of fodder after the invasion of Dreissena bugensis, may indicate the attainment of specific limit reproductive capacity of this species.

Differential ontogenetic effects of gut passage through fish on seed germination

Passage through the digestive tract of frugivorous vertebrates likely influences seed dormancy, time to germination, and/or future seedling growth. Effects of gut passage on seed germination have been extensively investigated among frugivorous birds and mammals, however, few studies have focused on frugivorous fish. Here we present the results of a feeding experiment focusing on a broadly distributed Amazonian frugivorous fish, Brycon falcatus, and a fig tree, Ficus gomelleira. We investigated the effects of gut passage and ontogeny on seed germination probability and speed. The probability of seed germination and germination speed increased for seeds defecated by fish relative to control seeds. We also detected a negative effect of intestine length, where germination probability and speed decreased when seeds passed through larger fish with greater intestine to body length ratio. Such effects are probably the result of ontogenetic diet shifts, in which young fish transition from carnivory to frugivory as adults; a process only revealed by the inclusion of both small juvenile and large adult individuals in our study. As such, we advance knowledge of the mechanisms involved in frugivory as a feeding habit among fishes and on animal-fruit mutualisms.

СООБЩЕСТВА РЫБ МЕЛКОВОДИЙ ОЗ.АЛАКОЛЬ В УСЛОВИЯХ ВОЗРАСТАЮЩЕЙ РЕКРЕАЦИОННОЙ НАГРУЗКИ

Indigenous fish fauna has high endemism to the Balkhash watershed.&nbsp; Area of indigenous fish species had been drastically reduced after negative human impact.&nbsp; The Alakol Lake still remains bigger refuge for indigenous fishes. Therefore investigation of growing recreational impact to fish population on shallow sites was the aim of our researches. Samples were collected during 2015-2017 by international recommendations. State of the young fishes was evaluated through up their biological characteristics. Data on size and condition factor of fish babies were presented first time for many species despite long history of fishes investigations in the Alakol Lake.&nbsp;&nbsp; Diversity indexes by Simpson and Shannon&nbsp; were calculated to describe fish communities. Only 5 indigenous fish species like Seven rivers’ minnow Phoxinus brachyurus, spotted stone loach Triplophysa strauchii, Sewertzov’s stone loach Triplophysa sewerzowii, plain thicklip loach Triplophysa labiata, and Balkhash perch Perca schrenkii were revealed. Alien fish species were presented by 4 species like carp Cyprinus carpio, Prussian carp Carassius gibelio, topmouth gudgeon or pseudorasbora Pseudorasbora parva, and rosy bitterling Rhodeus ocellatus. Grow rate and condition factor indicated rather good living conditions for the indigenous fishes. Alien short living fish species were not neither numerous nor permanent members of the fish assemblages. The presented data allowed us to consider modern state of shallow sites of the lake as good enough for the indigenous fish reproduction.&nbsp; Limitation of number of visitors and 300 meters wide protected area around the investigated sites should be reasonable for long term conservation of indigenous fish fauna in the Alakol Lake.&nbsp; Key words: Alakol Lake, recreational, indigenous, alien, fish fauna

Changes in the biochemical status of common carp juveniles (Cyprinus carpio L.) exposed to ammonium chloride and potassium phosphate

Biogen elements that enter the water in large quantities are one of the main pollutants in the aquatic environment. They lead both to eutrophication of the reservoir and a decrease in the viability of young fish, acting as toxin. The energy enzyme activity (lactate dehydrogenase and succinate dehydrogenase), nitrogen (glutamate dehydrogenase) metabolism, dephosphorylation processes, and immune protection (by alkaline phosphatase activity) under the long-term action of ammonium nitrogen and phosphorus phosphates was studied. The biological object of research were 30–45 day common carp juveniles (Cyprinus carpio L.). According to our results, the peculiarities of the adaptive reactions of young carp to the action of these compounds have been established. We revealed, that under the loading of ammonium nitrogen, the activity of the processes of anaerobic digestion of energy-intensive complex increases directly in the organs of neutralization and excretion of nitrogenous compounds, namely in the gills. In general, the body of the carp due to these actions reduces the total energy consumption for maximum survival in these environmental conditions. We registered, that under the influence of elevated concentrations of phosphorus phosphates, oxidation of biogen elements to the body's energy needs in the presence of oxygen was observed. The processes of immune defense and dephosphorylation, for which LPh is responsible, also the detoxification, the excretion of nitrogenous substances from the body of carp (GDG) occurred differently depending on the chemical nature of the toxin. Thus, under the influence of ammonium nitrogen there was an increase in the activity of LPh in the highest concentrations of the toxin, and the activity of GDG decreased to reduce the production of ammonia, to avoid endogenous intoxication. Through these load of potassium monophosphate, the rise in the activity of immune defense processes and the involvement of ammonia in the cycle of tricarboxylic acids due to reamination to the energy supply of the processes of counteracting the weak but chronic toxic effects of orthophosphate ion. Under the load of ammonium chloride was observed not only the use of “traditional” energy substrates - glycogen and lipids, as well as proteins, which indicates the high toxicity of this compound for the body of young carp. Through the action of orthophosphate ion, the active use of lipids and even the activation of gluconeogenesis at maximum concentrations, as a reaction to weak long-term chemical stress.

Parasites of sturgeon fish in the conditions of artificial reproduction in the Astrakhan region

Due to the reduction of stocks of valuable sturgeon species, the restoration of which is difficult due to the lack of natural reproduction, limited scale and low efficiency of artificial reproduction, the development of sturgeon breeding in the Astrakhan region in recent decades remains the most relevant direction of the fishing industry. The main damage to fish farms is caused by infectious and invasive diseases. Epizootic well-being of enterprises depends largely on timely applied preventive measures, ichthyopathological monitoring and production control. This paper presents the results of a parasitological survey of different age groups of sturgeon fish in conditions of artificial reproduction, which is one of the methods for assessing the epizootic situation on a fish farm. The parasitofauna of Russian sturgeon and Beluga combined ectotrophic organisms of a direct development cycle widely distributed in aquaculture — protozoa, crustaceans, leeches. Producers of Beluga and sturgeon larvae each have two types of parasites with a low level of infestation. Producers of Russian sturgeon were distinguished by their parasitic purity. The qualitative composition of parasites of young sturgeon fish grown in ponds was more diverse and in different years included 5-6 species with a predominance in young Russian sturgeon. This age group had the highest level of invasion by epizootically significant parasites. The 35 % of the examined fish had mixed infestations. The parasite fauna of larvae and juveniles of Russian sturgeon and Beluga combined common species: Ichthyophthirius multifiliis and Ichthiobodo necatоr. The detected organisms did not show pathogenicity to their host, but the presence of parasites with a high epizootic potential indicates the preservation and functioning of the centers of infestation on the farm.