Severe hypoxia exposure inhibits larval brain development but does not affect the capacity to mount a cortisol stress response in zebrafish

Fish nursery habitats are increasingly hypoxic and the brain is recognized as highly hypoxia-sensitive, yet there is a lack of information on the effects of hypoxia on the development and function of the larval fish brain. Here, we tested the hypothesis that by inhibiting brain development, larval exposure to severe hypoxia has persistent functional effects on the cortisol stress response in zebrafish (Danio rerio). Exposing 5 days post-fertilization (dpf) larvae to 10% dissolved O2 (DO) for 16 h only marginally reduced survival, but it decreased forebrain neural proliferation by 55%, and reduced the expression of neurod1, gfap, and mbpa, markers of determined neurons, glia, and oligodendrocytes, respectively. The 5 dpf hypoxic exposure also elicited transient increases in whole body cortisol and in crf, uts1, and hsd20b2 expression, key regulators of the endocrine stress response. Hypoxia exposure at 5 dpf also inhibited the cortisol stress response to hypoxia in 10 dpf larvae and increased hypoxia tolerance. However, 10% DO exposure at 5 dpf for 16h did not affect the cortisol stress response to a novel stressor in 10 dpf larvae or the cortisol stress response to hypoxia in adult fish. Therefore, while larval exposure to severe hypoxia can inhibit brain development, it also increases hypoxia tolerance. These effects may transiently reduce the impact of hypoxia on the cortisol stress response but not its functional capacity to respond to novel stressors. We conclude that the larval cortisol stress response in zebrafish has a high capacity to cope with severe hypoxia-induced neurogenic impairment.

TEKNIS PRODUKSI PEMBENIHAN DAN PENDEDERAN IKAN LEMON ALGAE EATER Gyrinocheilus aymoneiri DI ADE’S FISH FARM, KABUPATEN BOGOR, JAWA BARAT

ABSTRACTLemon fish Algae Eater is one of the aquarium fish which is well-known as Algae Eater. The Lemon Algae Eater is placed in a pond measuring 2 m x 3 m x 0.8 m, with a water height of 50 cm. For optimum health, feed the Algae Eater with Feng Li pellets by having a restricted feeding method or this can also be limited to 5% from the brood fish weight. The semi-natural hatchery of Lemon fish Algae Eater is needed. An aquarium (100cm x 60 cm x 50 cm) with a water height of 30 cm is needed for the hatchery of Lemon fish Algae Eater eggs. The average fecundity of Lemon fish Algae Eater eggs produced in 1 spawning can reache up to 84 742 eggs with the average of Fertilization Rate is 79%, the Hatching Rate is 83%, and the Survival Rate is 74%. The Lemon Algae Eater eggs will hatch in 10-12 hours. Fish nursery of lemon fish algae eater is used pond measures 3 m x 2 m x 1.5 m. The freshly hatched larvae are harvested at the age of 30 days and 45 days with a size of 1.2-1.5 cm/fish and 2.5-3 cm/fish. ABSTRAKLemon algae eater merupakan salah satu ikan aquarium yang dikenal sebagai pemakan alga. Pemeliharaan ikan lemon algae eater dilakukan pada bak beton yang berukuran 2 m x 3 m x 0.8 m, dengan tinggi air 50 cm. Pakan yang diberikan berupa pelet feng li dengan metode pemberian pakan restricted atau metode dibatasi dengan 5% dari bobot induk. Pemijahaan induk ikan lemon algae eater dilakukan secara semi alami. Wadah penetasan telur ikan lemon algae eater menggunakan akuarium ukuran 100 cm x 60 cm x 50 cm dengan tinggi air 30 cm. Rata-rata fekunditas telur ikan lemon algae eater yang dihasilkan dalam 1 kali pemijahan mencapai 84 742 butir telur dengan memiliki nilai rata-rata Fertilization Rate sebesar 79%, Hatching Rate sebesar 83%, dan Survival Rate sebesar 74%. Telor ikan lemon algae eater akan menetas dalam waktu 10-12 jam. Kegiatan pendederan ikan lemon algae eater menggunakan wadah bak beton yang berukuran 3 m x 2 m x 1.5 m. Benih yang dipanen berumur 30 hari dan 45 hari dengan ukuran 1.2 -1.5 cm/ekor dan 2.5 - 3 cm/ekor.

Predation on small juvenile fishes in shallow estuarine nursery areas: Reply to Baker & Sheaves (2021)

The key criticism by Baker & Sheaves (2021; Mar Ecol Prog Ser 662:205-208) of the Whitfield (2020; Mar Ecol Prog Ser 649:219-234) estuarine littoral predation paradigm review is that shallow water fish nursery habitats contain abundant predator assemblages which may create high predation pressure on the juvenile fish cohorts that occupy these areas. The primary arguments supporting Baker & Sheaves’ criticism arise from a series of papers published by them on piscivorous fish predation in certain tropical Australian estuaries. The counter-argument that shallow littoral areas in estuaries do indeed provide small juvenile fishes with refuge from small and large piscivorous fishes is provided by published papers from 4 different estuary types in South Africa, covering both subtropical and warm-temperate systems. Based on the overall published information, the argument for shallow (<1 m depth) estuarine waters providing major protection for newly settled juveniles appears to be weak in northern Australia but strong in South Africa. The global situation, as outlined in this response, is more supportive of low piscivorous predation in shallow nursery habitats, but further targeted research is needed before we can confirm that littoral estuarine waters are indeed a universal keystone attribute in this regard.

Macrophytes banks as potential fish nursery areas in small hydropower reservoirs

Aim This study verified if the macrophyte banks found in two reservoirs of small hydroelectric plants (SHPs) have a functional ecological role for the initial development of ichthyofauna. Additionally, we compared the differences in the structure of the fish assemblages along each reservoir compartment and between reservoirs. Methods Sampling was performed in March 2018, in lotic, intermediate, and lentic compartments of Palmeiras and Retiro reservoirs, Sapucaí-Mirim River (SP). Three distinct macrophyte banks in each stretch (triplicates), considering the most representative in terms of composition (recurrency/dominance), were sampled, resulting in 18 samples (nine per reservoir). For fish collection we used a sieve of 1 m2 of area, mesh size of 1 mm, which was manually hauled, from the boat, in the marginal aquatic vegetation (three hauls per sample). Simultaneously, we measured basic limnological parameters with a Horiba U-52 water probe, adjacent to the banks. Results The presence of juveniles of all fish orders found in the river, Characiformes, Siluriformes, Synbranchiformes, Gymnotiformes and Cichliformes, demonstrates that, at least in certain moment of their development cycle, the macrophyte banks are used by species with different ecological requirements. It was observed significant statistical differences in the structure of the ichthyofauna along the longitudinal axes of the reservoirs, but not between reservoirs. The same was seen for the limnological data (PCA). Conclusions The macrophyte banks found in the SHPs reservoirs have a potential role as nurseries for the local ichthyofauna, mainly, but not exclusively, for sedentary species and with parental care. This association is ecologically relevant, given the absence of typical lateral habitats for the initial development of the fish fauna. Additionally, despite the reservoirs small size, spatial organization was also important for the assemblage’s structure, with differences in terms of composition, size and development stages along the distinct sampling stretches.

Littoral habitats as major nursery areas for fish species in estuaries: a reinforcement of the reduced predation paradigm

For many decades, the role of estuaries as important nursery areas for fishes was accepted as fact by scientists and environmental managers. At the turn of the 21st century, a question mark was raised in relation to the reduced predation component of the nursery function, with some scientists contending that both large and small piscivorous fish species had access to the estuarine habitats that juvenile fishes in estuaries occupied. If true on a global scale, the nursery designation for these habitats would be compromised and the long-held paradigm that estuaries are important nursery areas for fishes would need to be revised. In this review, I examine the nature of fish nursery areas in estuarine littoral habitats from a mainly predation perspective and, based on a variety of ichthyofaunal and avifaunal studies, come to the conclusion that apart from a few selected estuarine systems, there is limited predation on juvenile fishes in these particular areas. This, coupled with the abundant suitable food resources for juvenile fish from different trophic categories, shelter from high-energy marine wave action and biological connectivity between a variety of submerged and emergent macrophyte communities, renders shallow estuarine littoral areas ideal nursery areas for the juveniles of mostly euryhaline marine fish species, the dominant component of estuarine ichthyofaunas globally. In addition, there are strong indications from the fossil record that these littoral estuarine nursery areas have been functioning since the Devonian, more than 350 million years ago.

Masculinization in common carp (Cyprinus carpio) by androgen immersion: The interaction effect of hormone concentration and immersion time

Synthetic androgens (male hormones) administered to fish nursery are being used in aquaculture to avoid sexual differentiation and unwanted spawning at the eggs or the first feeding fry stage of fish. Present trial was conducted with the aim to produce male common carp (Cyprinus carpio) by egg immersion technique. Through this little insight, the effect of different hormone concentrations (17α-methyltestosterone @ HC:150, 300, 450 and 600 µgl-1) with immersion times (IT: 24, 48 and 72 hrs) and their interaction effect (HC x IT) on the hatching percentage of Cyprinus carpio eggs, percent survival and percent of male’s production was evaluated specifically. Results showed that egg hatching percentage decreased with increased IT likewise, survival of treated fry was affected by increasing the IT (P<0.001). The main interaction effect of HC x IT showed that the highest percent of male individuals (95%) was obtained at 450-600 µgl-1 HC for 72 hrs IT, followed by 88-92.50% at 150-300 µgl-1 HC for 72-hrsof IT, 87.50% at 48-hrs of IT for rest of the hormone treatments, and lowest 47.50% was recorded in control (P<0.05). Increased percent male of Cyprinus carpio was obtained with increasing HC across all ITs. It was observed that the immersion treatment at 600µgl-1 for 72 hours was more effective to change the sex ratio of pre hatch Cyprinus carpio. A comparative outlook made from this experimental trial that sex induction of Cyprinus carpio by eggs immersion using synthetic male steroid hormone is an alternative safe technique of fish sex reversal in contrast to oral administration of hormone in fish feed.

Fish nursery value of algae habitats in temperate coastal reefs

The nursery function of coastal habitats is one of the most frequently mentioned and recognized ecosystem services in the valuation of coastal ecosystems. Despite its importance our understanding of the precise habitat parameters and mechanisms that make a habitat important as a nursery area is still limited for many species. The study aimed to establish the importance of different algae morphotypes in providing shelter and food for juvenile coastal fish during the main settlement peaks, in early spring and late summer, in littoral rocky reef systems in the Northwestern Mediterranean. The results of our study showed strong seasonal differences in algae cover, composition and height between the two sampling periods. Overall, during spring the algae were well developed, while in late summer, both density and height, of most algae decreased considerably. Equally, prey biomass, in form of suitable sized invertebrate fauna associated to the algae, decreased. Accordingly, the shelter and food for the fish settling in this habitat during late summer were less abundant, indicating a mismatch between the observed presence of juvenile fish and optimal habitat conditions. Differences in prey densities were detected between algae morphotypes, with structurally more complex algae, such as Cystoseira spp. and Halopteris spp. consistently containing more prey, independent of season, compared to simpler structured morphotypes such as Dictoytales. The study furthermore related juvenile fish density to habitats dominated by different algae morphotypes. Out of the three-study species (Diplodus vulgaris, Symphodus ocellatus, Coris julis) only S. ocellatus showed a significant association with an algae habitat. S. ocellatus related positively to habitats dominated by Dictoytales which provided the highest cover during late summer but had the lowest prey densities. A strong association of this species with Cystoseira, as reported by other studies, could not be confirmed. Cystoseira was abundant within the study area but in a state of dieback, showing loss and reduced height of foliage, typical for the time of year within the study area. It is therefore likely that algae-fish associations are context-dependent and that several algae species may fulfil similar functions. We also discovered that prey biomass did not appear to have an important effect on juvenile abundances. Nevertheless, the availability of prey may influence juvenile fish condition, growth performance and ultimately long-term survival. We therefore suggest that future studies on habitat quality should also include, besides abundance, indicators related to the condition and growth of juveniles.