Search

Intensive research on the effectiveness of chemoattractants has been widely explored to improve the feed qualities in expanding crustacean farming. Taste preferences in slipper lobster remained unknown despite their significant contribution to the lobster fisheries. Chemoattractants allow better performance in aquaculture species by increasing food attractiveness and palatability. Amino acids (AA) have been leading in previous research on crustacean feeding behavior. Given that slipper lobster possesses chemoreceptors to detect and orient towards food, this study investigated an approach to identify the AA with the most potent chemoattractant in eliciting a response from slipper lobster. Behavioral assays were performed to evaluate the responses of slipper lobster Thenus orientalis (carapace length, 52.34 ± 1.52 mm) on 15 crystalline AA and three derivatives of AA (DAA) at three concentrations between 10-1 and 10-3 3 M as test substances (TS). Meretrix sp. extract was used as a positive control and clean filtered seawater as a negative control. The behavioral responses of 14 T. orientalis were evaluated based on their antennular flicking rate, third maxillipeds activity, and substrate probing by the pereiopods. T. orientalis responded to the solutions of single AA down to a concentration of 10-3 M, excluding histidine and serine. The behavioral activity displayed by T. orientalis increased with the TS concentrations. L-glutamic acid monosodium salt monohydrate, betaine, and glycine solutions elicited the most behavioral responses, whereas histidine exhibited the lowest behavioral responses. Conclusively, L-glutamic acid monosodium salt monohydrate, betaine, and glycine can be potential chemoattractants for T. orientalis. [ABSTRACT FROM AUTHOR]

Context: Swimming crab is a vital fishery resource and a valuable source of income in the southern East China Sea, but it lacks management strategies, especially when using different fishing gear. Aims: This study aimed to determine the effects of spatial–temporal conditions and vessel capacity on swimming crabs by using different fishing-gear types in the Taiwan Strait (TS). Methods: We used generalised linear mixed models (GLMMs) to investigate data from Taiwanese vessels (2011–2019) on how spatial–temporal conditions and vessel capacity affected the catch of swimming crabs when using trawls, gill-nets and traps. Key results: The results showed that the traps (>80.0%) caught more swimming crabs in the TS than did the gill-nets (6.6%) and trawls (8.0%). Additionally, the GLMM analysis showed that Charybdis feriatus , Portunus pelagicus and Portunus sanguinolentus catches by traps and trawls were significantly affected by different fishing locations, climate events, work hours and vessel sizes. However, for gill-nets, spatial–temporal conditions and vessel capacity did not affect the catch of C. feriatus. Conclusions: Monitoring fishing efforts and environmental factors is vital to understanding their impacts on marine ecosystems. Implications: These findings enable future sustainable crab fishing through harvesting strategy planning, ecosystem management and spatial–temporal governance. The catch performance of fishing gear depends on species' behaviour, habitat, fishing grounds, fishing regulations and oceanographic conditions. Besides, to optimise the catch, experienced fishermen mostly use the right gear at the right time and place. Therefore, the fact that baited traps more efficiently target swimming crabs than do other gear types may be due to two critical factors, namely, the habitat of the crabs in the benthic area and the chemoreceptive sensory behaviour of crabs in detecting the bait. [ABSTRACT FROM AUTHOR]

Mesocyclops leuckarti is a zooplankton that is potentially suitable as a live food for freshwater fish larvae. Aquaculture farmers often struggled to create nutritious live feed to maximize the production of larval fish. This study aimed to determine the effects of different enrichments on life-table parameters, protein, lipid and fatty acid content of M. leuckarti when enriched with different dietary enrichments. In this study, five treatments for raising the copepod were compared: rice bran, soybean meal, Chlorella sp., Spirulina sp., and unenriched (control). The results showed that M. leuckarti after 16 days of cultivation enriched with rice bran produced a higher population density (53.3 ind/ml) and survival rate (97.4%) than when cultivated with any of the other diets. In terms of nutritional value, protein content was higher in M. leuckarti enriched with rice bran (52% DW) and soybean meal (53% DW). However, lipid content was highest in M. leuckarti enriched with rice bran (14% DW). Fatty acids, such as α -linolenic acid ALA (7.21%) and docosahexaenoic acid DHA (6.26%) were higher in M. leuckarti enriched with rice bran. Eicosapentaenoic acid EPA (7.16%) and arachidonic acid ARA (7.74%) were higher in M. leuckarti enriched with Chlorella sp. This study suggests that organic by-products are better sources for strengthening and improving the growth performance and life history of this copepod, and possibly also of zooplankton organisms in general. [ABSTRACT FROM AUTHOR]

In this study, climbing perch larvae were administrated with different diet treatments: Artemia nauplii enriched with 108 CFU mL−1L. lactis (LA); nauplii enriched with 0.5 g L−1 sodium alginate (SA); nauplii enriched with 0.5 g L−1 sodium alginate containing 108 CFU mL−1L. lactis (LSA); and non-enriched nauplii as the control (A). Throughout the 14-day observation period, fish larvae survival rate significantly increased to 50% (P <.05) in the group fed with LSA, followed by LA (41.7%) and SA (31.7%) while only 20% survival rate was observed in the control. The highest lysozyme activity was recorded in LSA (13.89 units mg−1 protein), followed by LA, SA, and A. Fish larvae treated with LA also showed a significant increase in lipase (P =.024) and amylase activities (P=.003) compared to those treated with LSA and SA. Our study indicated that L. lactis and alginate or the combination of both treatments (LSA) could improve the survival rate by upregulating their innate immune response. [ABSTRACT FROM AUTHOR]

The jewel cichlid Hemichromis bimaculatus is a popular freshwater ornamental fish with high market demand. However, it is aggressive and difficult to be maintained in captivity. Background colours are known to influence fish aggression, but there is still no such information available on H. bimaculatus. This study was conducted to examine the influence of 6 background colours (black, white, blue, yellow, green or red) on the aggression (chasing frequency), survival, weight gain and feed intake of the H. bimaculatus, through a 60‐day culture trial. At the end of this trial, since the total feed intake and fish weight gain (except black) were similar among all treatments, the green was the most recommended background colour for the H. bimaculatus culture as it has the highest fish survival, followed by the white and yellow. Low fish survival was found under the black, red and blue; hence, these background colours were not recommended. In this study, we suspected that different background colours may induce different aggressiveness degree in the H. bimaculatus, and biting may have occurred to cause low fish survival. Also, the blue was speculated to be a stressful background colour to the H. bimaculatus. Nevertheless, further study is necessary to elucidate these hypotheses. [ABSTRACT FROM AUTHOR]

The cladocera Moina macrocopa serves as a common live feed that is suitable for most freshwater fish species. Seven diets for the cladocera, viz. Chlorella sp., rice bran, soybean meal, chicken manure, swiftlet waste, canola oil, and artificial micro pellet were compared in this study. This study's objective was to analyse the effect of enriched M. macrocopa on the growth, survival, and dietary profiles of hybrid Nile tilapia fry. The feeding experiment lasted for over 60 days. The M. macrocopa enriched with rice bran has produced the highest weight gain (5.83 g), survival (86.67%), protein (24.88%), and lipid (6.85%) in Nile tilapia fry. While, fatty acid such as α-linolenic acid (ALA; 4.67%) was found to be the highest in fry fed with M. macrocopa enriched with soybean meal. Arachidonic acid (ARA; 3.69%) and docosahexaenoic acid (DHA; 0.47%) were the highest in tilapia fry fed with M. macrocopa enriched with rice bran, while eicosapentaenoic acid (EPA; 6.33%) was the highest in tilapia fry fed with M. macrocopa enriched with Chlorella sp. In conclusion, the manipulation of nutrient such as protein, lipid and fatty acid Scompositions in M. macrocopa diet has successfully improved the nutrient compositions and production of Moina sp. culture that indirectly increased the growth and survival of hybrid tilapia fry. [ABSTRACT FROM AUTHOR]

The aquaculture of decapod crustaceans is expanding continuously to supply protein source for human consumption. Therefore, intensive research is necessary to improve the quality of the feeds in decapod crustacean farming. Decapod crustaceans are slow feeders, and dietary inclusion of plant proteins reduces their intakes on the feeds. Dietary supplementation of chemoattractants (CA) (to reduce food searching duration) and feeding stimulants (FS) (to stimulate ingestion) is therefore necessary to solve these problems respectively. Amino acids are commonly used as the CA and FS in aquaculture, and the feeding response of aquatic animals to amino acids is species‐specific. As the chemosensory systems of decapod crustaceans are complicated, and their feeding responses are different from fish, it is essential to understand which amino acids can function as the CA, FS or both to the targeted farmed species. This review provides an overview on the acceptance of some commercially farmed decapod crustaceans to amino acids. Topics related to the efficiency of amino acids being a CA and FS were discussed, and recommendations on how to present amino acids as a CA and FS efficiently in decapod crustacean farming were also made. [ABSTRACT FROM AUTHOR]

Rapid development has been associated with mercury pollution in the aquatic environment, leading to mercury toxicity in fish and other aquatic organisms. Histopathological abnormalities such as hyperplasia, inflammation, and necrosis have been observed in various fish tissues as a result of mercury contamination based on organic mercury (methylmercury) and inorganic mercury (mercuric chloride) exposure via dietary or water exposure, respectively, with different duration doses of mercury. Knowing that tissue changes occurred at an important part of each organ that played various critical roles in the normal physiological actions of fish, it is critical to understand how fish respond to mercury contamination and how this heavy metal element affects their general well-being. This review paper focuses on major tissue histopathology changes in response to mercury toxicity and their potential use as a mercury contamination indicator in fish. [ABSTRACT FROM AUTHOR]

The Amur ide (Leuciscus waleckii) is a fish in the Cyprinidae family. Compared with other Amur ide living in freshwater ecosystems, the Amur ide population in Lake Dali Nor of China is famous for its high tolerance to the alkaline conditions of 54 mM (pH 9.6). Yet, surprisingly, the ionoregulatory mechanism responsible for this remarkable alkaline adaptation remains unclear. Therefore, this study sought to investigate how bicarbonate affects the acid-base balancing and ionoregulatory responses of this animal. Here, using a comparative approach, the alkali form of Amur ide and its ancestral freshwater form living in other freshwater basins were each exposed to 50 mM (pH 9.59 ± 0.09), a level close to the alkalinity of Lake Dali Nor, and their physiological (AE1) adjustment of ions and acid-base regulation were investigated. This study highlighted differences in blood pH and serum ions (e.g., Na+, K+, Cl−, and Ca2+), Na+/K+ ATPase (NKA) activity and its mRNA level, and mRNA expression of gill transporters (Na+/H+ exchanger member 2 and/or 3, Na+/ HCO 3 - cotransporter (NBC1), Cl−/ HCO 3 - exchanger, Na+/Cl− cotransporter (NCC), Na+/K+/2Cl− (NKCC1), SLC26A5, and SLC26A6) for alkalinity adaptation between the two forms of Amur ide differing in alkalinity tolerance. Specifically, close relationships among the serum Na+ and mRNA levels of NCC, NKCC1, and NHE, and also NKA and NBC1, in addition to serum Cl− and bicarbonate transporters (e.g., SLC26A5 and SLC26A6), characterized the alkali form of Amur ide. We propose that this ecotype can ensure its transepithelial Cl− and Na+ uptake/base secretions are highly functional, by its basolateral NKA with NBC1 and apical ionic transporters, and especially NCC incorporated with other transporters (e.g., SLC26). This suggests an evolved strong ability to maintain an ion osmotic and acid-base balance for more effectively facilitating its adaptability to the high alkaline environment. This study provides new insights into the physiological responses of the alkaline form of the Amur ide fish for adapting to extreme alkaline conditions. This information could be used as a reference to cultivating alkaline-tolerant fish species in abandoned alkaline waters. [ABSTRACT FROM AUTHOR]

Climate warming and low pH environment are known to negatively impact all levels of aquatic organism from cellular to organism and population levels. For ammonotelic freshwater species, any abiotic factor fluctuation will cause disturbance to the fish, specifically at the gills which act as a multifunctional organ to support all biological processes. Therefore, this study was designed to investigate the effect of temperature (28 vs. 32°C) and pH (7.0 vs. 5.0) stress on the gill plasticity of Hoven's carp after 20 days of continuous exposure. The results demonstrated that high temperature and low pH caused severe changes on the primary and secondary lamellae as well as the cells within lamellae. An increasing trend of the proportion available for gas exchange was noticed at high temperature in both pH exposures, which resulted from a reduction of the primary lamellae width with elongated and thinner secondary lamellae compared to fishes at ambient temperature. Following exposure to high temperature and acidic pH, Hoven's carp experienced gill modifications including aneurysm, oedema, hypertrophy, curling of secondary lamellae, epithelial lifting, hyperplasia and lamellae fusion. These modifications are indicators of the coping mechanism of Hoven's carp to the changing environment in order to survive. [ABSTRACT FROM AUTHOR]

Leuciscus waleckii is a freshwater fish that is known to inhabit the Dali Nor Lake, Inner Mongolia, China. The water in this lake has an HCO3–/CO32– concentration of 54 mM (pH 9.6) and a salinity of 0.6‰. The physiological mechanisms that allow this fish to tolerate these saline/alkaline conditions have yet to be elucidated. Transcriptional component analysis has shown that the expression levels of a large number of genes involved in the pathways responsible for osmo-ionoregulation and arachidonic acid metabolism pathway expression change significantly (p < 0.05) during the regulation of acid–base balance under high alkaline stress. In this study, we investigated the role of long non-coding RNAs (lncRNAs) during adaptation to high alkaline conditions. Fish were challenged to an NaHCO3-adjusted alkalinity of 0 mM, 30 mM (pH 9.44 ± 0.08), and 50 mM (pH 9.55 ± 0.06) for 20 days in the laboratory. Gill and kidney tissues were then collected for high-throughput sequencing assays. A total of 159 million clean reads were obtained by high-throughput sequencing, and 41,248 lncRNA transcripts were identified. Of these, the mean number of exons and the mean length of the lncRNA transcripts were 4.8 and 2,079 bp, respectively. Based on the analysis of differential lncRNA transcript expression, a total of 5,244 and 6,571 lncRNA transcripts were found to be differentially expressed in the gills and kidneys, respectively. Results derived from Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of the coding genes were correlated with the lncRNA expression profiles. GO analysis showed that many lncRNAs were enriched in the following processes: "transporter activity," "response to stimulus," and "binding." KEGG analysis further revealed that metabolic pathways were significantly enriched. A random selection of 16 lncRNA transcripts was tested by RT-qPCR; these results were consistent with our sequencing results. We found that a large number of genes, with the same expression profiles as those with differentially expressed lncRNAs, were associated with the regulation of acid–base balance, ion transport, and the excretion of ammonia and nitrogen. Collectively, our data indicate that lncRNA-regulated gene expression plays an important role in the process of adaptation to high alkaline conditions in L. waleckii. [ABSTRACT FROM AUTHOR]

In the presence of I Moina i juice, the free neuromast-intact fish ingested significantly higher ( I p i < 0.05) proportion of live I Moina i (11.9 ± 9.3%) than frozen I Moina i (1.9 ± 2.7%), indicating that the mechanoreception facilitated prey detection. The I Moina i remaining in the beaker were detected using the naked eye, counted and the ingestion of I Moina i was calculated as [(number of I Moina i eaten/total number of I Moina i given) × 100]. Vision-mediated feeding behaviour of early juvenile Sultan fish, Leptobarbus hoevenii Keywords: ingestion rates; Jelawat; prey detection; sensory organs EN ingestion rates Jelawat prey detection sensory organs 1784 1787 4 03/13/21 20210401 NES 210401 The Sultan fish, or "Jelawat", I Leptobarbus hoevenii i is a cyprinid with a natural distribution in streams, rivers and lakes of some Southeast Asian countries, including Malaysia and Thailand (Mohsin & Ambak, 1983; Vidthayanon et al., 1997). [Extracted from the article]

This study investigated the effect of dietary arachidonic acid (ARA, 20:4n‐6) on final maturation, spawning performance and composition of the gonad of black sea urchin (Diadema setosum). Four different dietary ARA levels of 0.3 g/kg (Control diet), 1.4 g/kg (ARA 1.4), 2.5 g/kg (ARA 2.5) and 3.7 g/kg (ARA 3.7) were prepared and tested in this feeding trial for 90 days. The result showed that growth in terms of weight was not relatively affected by dietary ARA. Gonadosomatic Index (GSI) of animals were gradually increased in all the diets throughout the trial. The highest GSI level (25.7 ± 3.16%) was observed in animals fed with the diet ARA 1.4. ARA content in the gonad proportionally increased with dietary ARA levels. The highest larval survival rate (85.5 ± 5.67%) was found in diet ARA 2.5. The results of this study indicate that ARA plays an important role in the reproduction functions of black sea urchin and supplementing an appropriate level of ARA in the broodstock diet could induce the final maturation and improve reproduction of black sea urchin, but a higher level of ARA (3.7 g/kg) seems to have a negative effect on both growth rate and GSI. [ABSTRACT FROM AUTHOR]

This study was performed to evaluate the effect of dietary natural carotenoid sources on skin colour enhancement of false clownfish Amphiprion ocellaris. The juvenile fish (initial body wt. 0.30 g) were fed with four experimental diets including (a) commercial feed (reference diet), (b) moist feed, (c) sweet potato (potato diet) and (d) dried gut weed Enteromorpha sp. (gut weed diet). Sweet potato and gut weed were used to boost up β‐carotene levels in the diets. There was no significant difference in final weight (0.51 ± 0.02 – 0.61 ± 0.01 g) and length (2.80 ± 0.02 cm) of fishes among treatments (p > 0.05) after 8 weeks. The survival rate of the fish in all dietary treatment was greater than 89%. Principal component analysis results showed that fish fed potato and gut weed diets performed brighter colour in skin with more orangeness, body and accumulated β‐carotene levels were higher than those fish fed with reference diet. Indicator a* value for the redness of fish fed potato diet (16.18 ± 0.59) and gut weed (14.36 ± 2.14) was also higher than fish fed reference diet (10.92 ± 0.82). The result of this study provided key information for developing dietary colour enhancement of ornamental fish by using cost‐effective feed ingredients (potato and gut weed) as natural supplemental carotenoid sources. [ABSTRACT FROM AUTHOR]

Ureotelic elasmobranchs require nitrogen for both protein growth and urea-based osmoregulation, and therefore are probably nitrogenlimited in nature. Mechanisms exist for retaining and/or scavenging nitrogen in the gills, kidney, rectal gland and gut, but as yet, the latter are not well characterized. Intestinal sac preparations of the Pacific spiny dogfish shark (Squalus acanthias suckleyi) incubated in vitro strongly reabsorbed urea from the lumen after feeding, but mucosal fluid ammonia concentrations increased with incubation time. Phloretin (0.25 mmol l-1, which blocked urea reabsorption) greatly increased the rate of ammonia accumulation in the lumen. A sensitive [14C]urea-based assay was developed to examine the potential role of microbial urease in this ammonia production. Urease activity was detected in chyme/intestinal fluid and intestinal epithelial tissue of both fed and fasted sharks. Urease was not present in gall-bladder bile. Urease activities were highly variable among animals, but generally greater in chyme than in epithelia, and greater in fed than in fasted sharks. Comparable urease activities were found in chyme and epithelia of the Pacific spotted ratfish (Hydrolagus colliei), a ureotelic holocephalan, but were much lower in ammonotelic teleosts. Urease activity in dogfish chyme was inhibited by acetohydroxamic acid (1 mmol l-1) and by boiling. Treatment of dogfish gut sac preparations with acetohydroxamic acid blocked ammonia production, changing net ammonia accumulation into net ammonia absorption.We propose that microbial urease plays an important role in nitrogen handling in the elasmobranch intestine, allowing some urea-N to be converted to ammonia, which is then reabsorbed for amino acid synthesis or reconversion to urea. [ABSTRACT FROM AUTHOR]

Temperature is an abiotic factor that affects various biological and physiological processes in fish. Temperature stress is known to increase the production of reactive oxygen species (ROS) that subsequently cause oxidative stress. Fish is known to evolve a system of antioxidant enzymes to reduce ROS toxicology. Glutathione peroxidase (GPx) family consists of key enzymes that protect fish from oxidative stress. In this study, full-length GPx1 cDNA (GenBank accession no. KY984468) of Tor tambroides was cloned and characterized by rapid amplification of cDNA ends (RACE). The 899-base-pair (bp) GPx1 cDNA includes a 576-bp open reading frame encoding for 191 amino acids, plus 28 bp of 5′-untranslated region (UTR) and 295 bp of 3′-UTR. Homology analysis revealed that GPx1 of T tambroides (Tor-GPx1) shared high similarity with GPx1 sequences of other fish species. The phylogenetic construction based on the amino acid sequence showed that Tor-GPx1 formed a clade with GPx1 sequences of various fish species. Real-time polymerase chain reaction (PCR) was performed to assess the levels of GPx1 gene expression in the liver and muscle of T tambroides under thermal stress. The results indicated that GPx1 gene expression was down-regulated under decreased temperature. However, there was no significant difference between GPx1 gene expression in fish exposed to high temperature and control. Our study provides the first data regarding GPx gene expression in T tambroides under thermal stress. [ABSTRACT FROM AUTHOR]

The mosquitofish (Gambusia affinis) naturally inhabits freshwater (FW; 1-3‰) and seawater (SW; 28-33‰) ponds in constructed wetland. To explore the physiological status and molecular mechanisms for salinity adaptation of the mosquitofish, cytoprotective responses and osmoregulation were examined. In the field study, activation of protein quality control (PQC) mechanism through upregulation of the abundance of heat shock protein (HSP) 90 and 70 and ubiquitin-conjugated proteins was found in the mosquitofish gills from SW pond compared to the individuals of FW pond. The levels of aggregated proteins in mosquitofish gills had no significant difference between FW and SW ponds. Furthermore, the osmoregulatory responses revealed that the body fluid osmolality and muscle water contents of the mosquitofish from two ponds were maintained within a physiological range while branchial Na+/K+-ATPase (NKA) expression was higher in the individuals from SW than FW ponds. Subsequently, to further clarify whether the cellular stress responses and osmoregulation were mainly induced by hypertonicity, a laboratory salinity acclimation experiment was conducted. The results from the laboratory experiment were similar to the field study. Branchial PQC as well as NKA responses were induced by SW acclimation compared to FW-acclimated individuals. Taken together, induction of gill PQC and NKA responses implied that SW represents an osmotic stress for mosquitofish. Activation of PQC was suggested to provide an osmoprotection to prevent the accumulation of aggregated proteins. Moreover, an increase in branchial NKA responses for osmoregulatory adjustment was required for the physiological homeostasis of body fluid osmolality and muscle water content. [ABSTRACT FROM AUTHOR]

Microplastic pollution in our environment, especially water bodies is an emerging threat to food security and human health. Inevitably, the outbreak of Covid-19 has necessitated the constant use of face masks made from polymers such as polypropylene, polyurethane, polyacrylonitrile, polystyrene, polycarbonate, polyethylene, or polyester which eventually will disintegrate into microplastic particles. They can be broken down into microplastics by the weathering action of UV radiation from the sun, heat, or ocean wave-current and precipitate in natural environments. The global adoption of face masks as a preventive measure to curb the spread of Covid-19 has made the safe management of wastes from it cumbersome. Microplastics gain access into aquaculture facilities through water sources and food including planktons. The negative impacts of microplastics on aquaculture cannot be overemphasized. The impacts includes low growth rates of animals, hindered reproductive functions, neurotoxicity, low feeding habit, oxidative stress, reduced metabolic rate, and increased mortality rate among aquatic organisms. With these, there is every tendency of microplastic pollution to negatively impact fish production through aquaculture if the menace is not curbed. It is therefore recommended that biodegradable materials rather than plastics to be considered in the production of face mask while recycle of already produced ones should be encouraged to reduce waste. [Display omitted] • Microplastic pollution not only threatened aquatic organisms but also to human through food chain. • Improper disposal of used face masks in the environment will lead to its disintegration into microparticles. • Negative impacts of microplastic includes disturb metabolism, increased neurotoxicity and mortality. [ABSTRACT FROM AUTHOR]

Many species from several different families of fishes perform mouthbrooding, where one of the sexes protects and ventilates the eggs inside the mouth cavity. This ventilation behaviour differs from gill ventilation outside the brooding period, as the normal, small-amplitude suction-pump respiration cycles are alternated with actions including near-simultaneous closed-mouth protrusions and high-amplitude depressions of the hyoid. The latter is called churning, referring to its hypothetical function in moving around and repositioning the eggs by a presumed hydrodynamic effect of the marked shifts in volume along the mouth cavity. We tested the hypothesis that churning causes the eggs located posteriorly in the mouth cavity to move anteriorly away from the gill entrance. This would prevent or clear accumulations of brood at the branchial basket, which would otherwise hinder breathing by the parent. Dual-view videos of female Nile tilapias (Oreochromis niloticus) during mouthbrooding showed that churning involves a posterior-to-anterior wave of expansion and compression of the head volume. Flow visualisation with polyethylene microspheres revealed a significant inflow of water entering the gill slits at the zone above the pectoral fin base, followed by a predominantly ventral outflow passing the ventrolaterally flapping branchiostegal membranes. X-ray videos indicated that particularly the brood located close to the gills is moved anteriorly during churning. These data suggest that, in addition to mixing of the brood to aid its oxygenation, an important function of the anterior flow through the gills and buccal cavity during churning is to prevent clogging of the eggs near the gills. [ABSTRACT FROM AUTHOR]

Interacting effects of feeding and stress on corticoid responses in fish were investigated in common carp fed 3.0% or 0.5% body mass (BM) which received no implant, a sham or a cortisol implant (250 mg/kg BM) throughout a 168 hour post-implant period (168 h-PI). At 12 h-PI, cortisol implants elevated plasma cortisol, glucose and lactate. Plasma osmolality and ions remained stable, but cortisol increased gill and kidney Na + /K + ATPase (NKA) and H + ATPase activities. Gill NKA activities were higher at 3%-BM, whereas kidney H + ATPase activity was greater at 0.5%-BM. Cortisol induced liver protein mobilization and repartitioned liver and muscle glycogen. At 3%-BM, this did not increase plasma ammonia, reflecting improved excretion efficiency concomitant with upregulation of Rhesus glycoprotein Rhcg-1 in gill. Responses in glucocorticoid receptors (GR1/GR2) and mineralocorticoid receptor (MR) to cortisol elevation were most prominent in kidney with increased expression of all receptors at 24 h-PI at 0.5%-BM, but only GR2 and MR at 0.5%-BM. In the liver, upregulation of all receptors occurred at 24 h-PI at 3%-BM, whilst only GR2 and MR were upregulated at 0.5%-BM. In the gill, there was a limited upregulation: GR2 and MR at 72 h-PI and GR1 at 168 h-PI at 3%-BM but only GR2 at 72 h-PI at 0.5%-BM. Thus cortisol elevation led to similar expression patterns of cortisol receptors in both feeding regimes, while feeding affected the type of receptor that was induced. Induction of corticoid receptors occurred simultaneously with increases in Rhcg-1 mRNA expression (gill) but well after NKA and H + ATPase activities increased (gill/kidney). [ABSTRACT FROM AUTHOR]

In the present study, the combined effects of hypoxia and nutritional status were examined in common carp ( Cyprinus carpio ), a relatively hypoxia tolerant cyprinid. Fish were either fed or fasted and were exposed to hypoxia (1.5–1.8 mg O 2 L − 1 ) at or slightly above their critical oxygen concentration during 1, 3 or 7 days followed by a 7 day recovery period. Ventilation initially increased during hypoxia, but fasted fish had lower ventilation frequencies than fed fish. In fed fish, ventilation returned to control levels during hypoxia, while in fasted fish recovery only occurred after reoxygenation. Due to this, C. carpio managed, at least in part, to maintain aerobic metabolism during hypoxia: muscle and plasma lactate levels remained relatively stable although they tended to be higher in fed fish (despite higher ventilation rates). However, during recovery, compensatory responses differed greatly between both feeding regimes: plasma lactate in fed fish increased with a simultaneous breakdown of liver glycogen indicating increased energy use, while fasted fish seemed to economize energy and recycle decreasing plasma lactate levels into increasing liver glycogen levels. Protein was used under both feeding regimes during hypoxia and subsequent recovery: protein levels reduced mainly in liver for fed fish and in muscle for fasted fish. Overall, nutritional status had a greater impact on energy reserves than the lack of oxygen with a lower hepatosomatic index and lower glycogen stores in fasted fish. Fasted fish transiently increased Na + /K + -ATPase activity under hypoxia, but in general ionoregulatory balance proved to be only slightly disturbed, showing that sufficient energy was left for ion regulation. [ABSTRACT FROM AUTHOR]

Exposure to heat-shock protein (Hsp) stimulating factors induces Hsp accumulation and confers tolerance to lethal ammonia stress on the common carp Cyprinus carpio. This study investigated whether a non-lethal heat shock bestowed similar protective effects against ammonia and induced thermotolerance, both thought to be rendered by increased amounts of Hsps. The 30-min lethal temperature (30 min LHT) and 1-h lethal ammonia concentration (1 h LCT) for this species occurred at 41°C and 14.2 mg/L NH3 respectively. Heating juvenile carp (5 cm) from 28°C to 32, 34 and 38°C, with a subsequent 8-h recovery period augmented tolerance to lethal heat and ammonia perturbation by two to threefold as compared with animals held at 28°C. Protection occurred in conjunction with Hsp70 accumulation in gills, substantiating the role of this Hsp in enhancing the stress tolerance of common carp. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this study was to investigate the interaction between feeding, exercise and cortisol on metabolic strategies of common carp over a 168h post-implant period. Feeding provided readily available energy and clearly increased muscle and liver protein and glycogen stores. Swimming, feeding and cortisol all induced aerobic metabolism by increasing oxygen consumption, and stimulated protein metabolism as demonstrated by the increased ammonia and urea excretion and ammonia quotient. Hypercortisol stimulated ammonia self-detoxifying mechanisms by enhancing ammonia and urea excretion, especially during severe exercise. At high swimming level, higher branchial clearance rates in cortisol treated fish succeeded in eliminating the elevation of endogenous ammonia, resulting in reduced plasma T amm levels compared to control and sham implanted fish. Carp easily induced anaerobic metabolism, both during routine and active swimming, with elevated lactate levels as a consequence. Both feeding and cortisol treatment increased this dependence on anaerobic metabolism. Hypercortisol induced both glycogenesis and gluconeogenesis resulting in hyperglycemia and muscle and liver glycogen deposition, most likely as a protective mechanism for prolonged stress situations and primarily fuelled by protein mobilization. [Copyright &y& Elsevier]

Abstract: Feeding and swimming can influence ion balance in fish. Therefore we investigated their impact on ionoregulation and its hormonal control in goldfish and common carp. As expected due to the osmorespiratory compromise, exhaustive swimming induced increases in gill Na+/K+ ATPase (NKA) activity in both species, resulting in stable levels of plasma ions. In contrast to our expectations, this only occurred in fed fish and feeding itself increased NKA activity, especially in carp. Fasting fish were able to maintain ion balance without increasing NKA activity, we propose that the increase in NKA activity is related to ammonia excretion rather than ion uptake per se. In goldfish, this increase in NKA activity coincided with a cortisol elevation whilst no significant change was found in carp. In goldfish, high conversion of plasma T4 to T3 was found in both fed and fasted fish resulting in low T4/T3 ratios, which increased slightly due to exhaustive swimming. In starved carp the conversion seemed much less efficient, and high T4/T3 ratios were observed. We propose that thyroid hormone regulation in carp was more related to its role in energy metabolism rather than ionoregulation. The present research showed that both species, whether fed or fasted, are able to sufficiently adapt their osmorepiratory strategy to minimise ions losses whilst maintaining gas exchange under exhaustive swimming. [Copyright &y& Elsevier]

Abstract: We examined the acute physiological responses to high environmental ammonia (HEA), particularly the linkages between branchial ammonia fluxes and unidirectional Na+ fluxes, as well as urea excretion, cortisol, and indicators of gill permeability in three freshwater teleosts differing in their sensitivities to ammonia; the highly sensitive salmonid Oncorhynchus mykiss (rainbow trout), the less sensitive cyprinid Cyprinus carpio (common carp) and the highly resistant cyprinid Carassius auratus (goldfish). Fish were acutely exposed to two sub-lethal ammonia concentrations (as NH4HCO3) at pH 7.9: 1mM for a period of 12h, identical for all species, and 5mM for the cyprinids and 1.4mM for the trout for 3h. Elevation of plasma cortisol at both levels of HEA was apparent in all species. At 1mM, ammonia excretion (J amm) was inhibited to a greater extent in trout than cyprinids and concurrently a significantly higher plasma ammonia level was evident in trout. However J amm was reversed in all species at 5 or 1.4mM. Goldfish showed a significant increase in urea excretion rate (J urea) during HEA exposure. In carp and trout, neither level of HEA elevated J urea but urea production was increased as evidenced by a considerable elevation of plasma urea. At 1mM HEA, Na+ imbalance became progressively more severe in trout and carp due to a stimulation of unidirectional Na+ efflux () without a concomitant increase in unidirectional Na+ influx (). Additionally, a transient reduction of was evident in trout. Goldfish showed an opposite trend for with reduced efflux rates and a positive Na+ balance during the first few hours of HEA. However, after 12h of exposure, both and were also increased in both carp and goldfish, whereas only was increased in trout, leading to a net Na+ loss. Na+ homeostasis was entirely disrupted in all three species when subjected to the 5 or 1.4mM ammonia for 3h: was significantly inhibited while considerable activation of was observed. Diffusive water efflux rates and net K+ loss rates across the gills were enhanced during HEA only in trout, indicating an increment in gill transcellular permeability. Transepithelial potential was increased in all the species during ammonia exposure, but to the least extent in goldfish. Overall, for several different physiological systems, trout were most disturbed, and goldfish were least disturbed by HEA, helping to explain the differential ammonia tolerance of the three species. [Copyright &y& Elsevier]

Abstract: Fish need to balance their energy use between digestion and other activities, and different metabolic compromises can be pursued. We examined the effects of fasting (7days) on metabolic strategies in goldfish and common carp at different swimming levels. Fasting had no significant effect on swimming performance (U crit) of either species. Feeding and swimming profoundly elevated total ammonia (T amm) excretion in both species. In fed goldfish, this resulted in increased ammonia quotients (AQ), and additionally plasma and tissue ammonia levels increased with swimming reflecting the importance of protein contribution for aerobic metabolism. In carp, AQ did not change since oxygen consumption (MO2) and T amm excretion followed the same trend. Plasma ammonia did not increase with swimming suggesting a balance between production and excretion rate except for fasted carp at U crit. While both species relied on anaerobic metabolism during exhaustive swimming, carp also showed increased lactate levels during routine swimming. Fasting almost completely depleted glycogen stores in carp, but not in goldfish. Both species used liver protein for basal metabolism during fasting and muscle lipid during swimming. In goldfish, feeding metabolism was sacrificed to support swimming metabolism with similar MO2 and U crit between fasted and fed fish, whereas in common carp feeding increased MO2 at U crit to sustain feeding and swimming independently. [Copyright &y& Elsevier]