Sarotherodon Melanotheron Heudelotii Research Articles

Kingdom of seashells: Explotation and culture of major commercial species

The effects of salinity on the variation of egg and oocyte densities and reproduction rate in the euryhaline tilapia <em>Sarotherodon melanotheron heudelotii</em> was investigated under natural and controlled conditions

Aquaculture in Sri Lanka: History, current status and future potential

The effects of salinity on the variation of egg and oocyte densities and reproduction rate in the euryhaline tilapia Sarotherodon melanotheron heudelotii was investigated under natural and controlled conditions

Skin coloration and habitat preference of the freshwater Anguilla eels

The effects of salinity on the variation of egg and oocyte densities and reproduction rate in the euryhaline tilapia <em>Sarotherodon melanotheron heudelotii</em> was investigated under natural and controlled conditions

Dealer’s perception towards aqua feeds-A case study of avanti feeds limited, Kovvur, West Godavari Dt. of Andhra Pradesh

The effects of salinity on the variation of egg and oocyte densities and reproduction rate in the euryhaline tilapia <em>Sarotherodon melanotheron heudelotii</em> was investigated under natural and controlled conditions

Effect of phytase supplementation on labeo rohita fingerlings that are fed by phytase supplemented ddgs based diet

The effects of salinity on the variation of egg and oocyte densities and reproduction rate in the euryhaline tilapia <em>Sarotherodon melanotheron heudelotii</em> was investigated under natural and controlled conditions

Salinity effects on oocytes, fertilized egg density and the reproduction rate of the tilapia Sarotherodon melanotheron heudelotii (Duméril, 1859) in natural and controlled environments

The effects of salinity on the variation of egg and oocyte densities and reproduction rate in the euryhaline tilapia <em>Sarotherodon melanotheron heudelotii</em> was investigated under natural and controlled conditions.

Adaptations of semen characteristics and sperm motility to harsh salinity: Extreme situations encountered by the euryhaline tilapia Sarotherodon melanotheron heudelotii (Dumeril, 1859)

In most teleost fishes, sperm cells are quiescent in the seminal plasma and are activated by either a drop (fresh water fish) or an increase in osmolality (marine fish) when released in the water. It is most interesting to examine how the mechanisms of sperm motility activation can adapt to a broad range of salinities, as applies to some euryhaline species, and particularly to the tilapia Sarotherodon melanotheron heudelotii, which can reproduce at salinities from 0 up to 120 in the wild. Here, the gonado-somatic index, semen characteristics, and the osmotic and ionic requirements of sperm motility activation were compared in S. m. heudelotii reared in fresh water (FW), sea water (SW), or hypersaline water (HW; salinities of 0, 35, and 70, respectively). No salinity-dependent differences were found in gonado-somatic index or semen characteristics, except for an increase of seminal plasma osmolality with increasing salinity (from 318 to 349 mOsm kg−1 in FW and HW fish, respectively). The osmolality range allowing the highest percentages of sperm activation broadened and shifted toward higher values with increasing fish ambient salinity (150–300, 300–800, and 500–1200 mOsm kg−1, for FW, SW, and HW fish, respectively). Nevertheless, at the three fish rearing salinities, sperm could be activated in media that were hypotonic, isotonic, or hypertonic relative to the seminal plasma, at least when some calcium was present above a threshold concentration. The [Ca2+] required for the activation of S. m. heudelotii sperm is (1) higher in fish reared at a higher salinity (2) higher in hypertonic than that in hypotonic activation media, whatever the fish rearing salinity, and (3) higher in the presence of Na+ or K+, the negative effects of which increased with an increase in fish rearing salinity. The [Ca2+]/[Na+] ​ ratios allowing for maximal sperm motility in SW or HW fish are close to those observed in natural environments, either in sea or hypersaline waters. In comparison to most teleosts with external fertilization, the total duration of sperm motility in S. m. heudelotii was exceptionally long (>2 hours regardless the fish rearing salinities). The decrease in sperm activity with increasing time since activation did not result from limiting energy reserves, as the addition of calcium in the activation medium caused most spermatozoa to become motile again. The comparison of sperm characteristics of S. m. heudelotii acclimated from FW to SW or HW with those of fish maintained all lifelong at their native salinity showed that adaptive responses were completed within 2 months or less.

Experimental evidence of complex relationships between the ambient salinity and the strontium signature of fish otoliths

The otolith strontium:calcium ratio (Sr:Ca) has been widely used to assess the connectivity between fish populations in ocean, estuarine and freshwater environments as the concentration of Sr in the otoliths is strongly correlated with water salinity. This correlation was tested experimentally in hypersaline conditions by submitting the extremely euryhaline tilapia species Sarotherodon melanotheron heudelotii (Cichlidae), found throughout West African continental waters and commonly used as an aquaculture species, to a strong salinity gradient (15–106). Experimental and control individuals were reared from birth in a closed system at a constant salinity of 10 and injected with oxytetracycline (OTC) to mark the otoliths at the beginning of the experiment. Randomly selected control fish were maintained for 75days at salinities of 10–20. The remaining experimental fish were acclimated to a salinity above 100 which was reduced by 10 each week to a salinity of 20. The salinity and temperature of the water were recorded every day and the Sr concentrations in the water were measured weekly by solution-based ICP-MS. The fish from the control and experimental groups were sampled weekly and otolith transverse sections were prepared for Sr:Ca measurements by laser ablation ICP-MS. No significant difference in the otolith growth rates after OTC marking was found between the control and experimental groups (ANCOVA, p=0.63), showing that the experimental design did not affect fish growth. The Sr concentration in the water was closely related to ambient salinity (positive linear regression, R2=0.96). For most of the fish tested (~80%), the relationship between otolith Sr:Ca and salinity was positive but nonlinear (power law, R2=0.77 on log–log plot). However, about 20% of individuals from both the control and the experimental groups showed consistently low Sr:Ca ratios irrespective of the salinity, suggesting that the Sr incorporation into the otoliths in these fish was strongly regulated. This shows that there is high variability between individuals in the regulation of Sr incorporation by a euryhaline species and indicates that otolith datasets for ecological applications should be interpreted with caution.

Plasticity of gene expression according to salinity in the testis of broodstock and F1 black-chinned tilapia, Sarotherodon melanotheron heudelotii.

The black-chinned tilapia Sarotherodon melanotheron heudelotii Rüppell 1852 (Teleostei, Cichlidae) displays remarkable acclimation capacities. When exposed to drastic changes of salinity, which can be the case in its natural habitat, it develops quick physiological responses and keeps reproducing. The present study focused on the physiological impact of salinity on male reproductive capacities, using gene expression as a proxy of acclimation process. Two series of experimental fish were investigated: the first one was composed of fish maintained in freshwater for several generations and newly acclimated to salinities of 35 and 70, whereas the second one consisted of the descendants of the latter born and were raised under their native salinity. Expression patterns of 43 candidate genes previously identified from the testes of wild males was investigated in the three salinities and two generations. Twenty of them showed significant expression differences between salinities, and their predicted function revealed that most of them are involved in the osmotic tolerance of sperm cells and/or in the maintenance of sperm motility. A high level of expression variation was evidenced, especially for fish maintained in freshwater. In spite of this, gene expression patterns allowed the differentiation between fish raised in freshwater and those maintained in hypersaline water in both generations. Altogether, the results presented here suggest that this high variability of expression is likely to ensure the reproductive success of this species under varying salinities.

Egg production in the euryhaline tilapia,Sarotherodon melanotheron heudelotii, experimentally maintained in fresh, sea and hypersaline waters

Through the experiments presented here we wanted to test whether egg production of the black-chinned tilapia Sarotherodon melanotheron heudelotii under experimental conditions varies as a function of ambient salinity (fresh waters vs. sea waters vs. hypersaline waters, 0, 35 and 70, respectively) and whether these responses differ between fish acclimated within a few weeks from fresh water to saline and hypersaline environments (experiments E1 and E2, monitoring over 10 and 18 weeks), and individuals born and raised all life long at the experimental salinities (E3, monitoring over 18 weeks). In total, 233 spawns were collected. In each of the three experiments, the reproductive investment (gram of egg per gram of female over 2 weeks) did not differ between salinities of 0 and 35, whereas it was 2–3 times lower at 70 than at 0–35, because of lower spawning frequency (E1-E3), smaller clutch size (E1) and lower spawn mass (E1-E3). Finally, fish acclimated to salinity from fresh water over a few weeks and those maintained at a particular salinity all life long showed similar reproductive traits, thereby emphasizing the remarkable physiological plasticity of this species.

Analysis of the black-chinned tilapiaSarotherodon melanotheron heudelotiireproducing under a wide range of salinities: from RNA-seq to candidate genes

The black-chinned tilapia Sarotherodon melanotheron heudelotii is an ecologically appealing model as it shows exceptional adaptive capacities, especially with regard to salinity. In spite of this, this species is devoid of genomic resources, which impedes the understanding of such remarkable features. De novo assembly of transcript sequences produced by next-generation sequencing technologies offers a rapid approach to obtain expressed gene sequences for non-model organisms. It also facilitates the development of quantitative real-time PCR (qPCR) assays for analysing gene expression under different environmental conditions. Nevertheless, obtaining accurate and reliable qPCR results from such data requires a number of validations prior to interpretation. The transcriptome of S.melanotheron was sequenced to discover transcripts potentially involved in the plasticity of male reproduction in response to salinity variations. A set of 54 candidate and reference genes was selected through a digital gene expression (DGE) approach, and a de novo qPCR assay using these genes was validated for further detailed expression analyses. A user-friendly web interface was created for easy handling of the sequence data. This sequence collection represents a major transcriptomic resource for S.melanotheron and will provide a useful tool for functional genomics and genetics studies.

An integrated fish–plankton aquaculture system in brackish water

Integrated Multi-Trophic Aquaculture takes advantage of the mutualism between some detritivorous fish and phytoplankton. The fish recycle nutrients by consuming live (and dead) algae and provide the inorganic carbon to fuel the growth of live algae. In the meanwhile, algae purify the water and generate the oxygen required by fishes. Such mechanism stabilizes the functioning of an artificially recycling ecosystem, as exemplified by combining the euryhaline tilapia Sarotherodon melanotheron heudelotii and the unicellular alga Chlorella sp. Feed addition in this ecosystem results in faster fish growth but also in an increase in phytoplankton biomass, which must be limited. In the prototype described here, the algal population control is exerted by herbivorous zooplankton growing in a separate pond connected in parallel to the fish–algae ecosystem. The zooplankton production is then consumed by tilapia, particularly by the fry and juveniles, when water is returned to the main circuit. Chlorella sp. and Brachionus plicatilis are two planktonic species that have spontaneously colonized the brackish water of the prototype, which was set-up in Senegal along the Atlantic Ocean shoreline. In our system, water was entirely recycled and only evaporation was compensated (1.5% volume/day). Sediment, which accumulated in the zooplankton pond, was the only trophic cul-de-sac. The system was temporarily destabilized following an accidental rotifer invasion in the main circuit. This caused Chlorella disappearance and replacement by opportunist algae, not consumed by Brachionus. Following the entire consumption of the Brachionus population by tilapias, Chlorella predominated again. Our artificial ecosystem combining S. m. heudelotii, Chlorella and B. plicatilis thus appeared to be resilient. This farming system was operated over one year with a fish productivity of 1.85 kg/m2 per year during the cold season (January to April).

Genetic diversity and adaptability of Sarotherodon melanotheron (Cichlidae) in coastal ecosystem

We analysed the genetic diversity of nine populations of two subspecies of Sarotherodon melanotheron using allozymes in relation to the existence of environmental pressures. The genetic variability of Sarotherodon melanotheron melanotheron in the Ivorian ecosystem (A = 1.23, He = 0.04 and P(95%) = 11.11) was lower than that of Sarotherodon melanotheron heudelotii of the estuaries in Gambia and Saloum (A = 1.68, He = 0.08 and P(95%) = 22.23). The analysis of allelic diversity revealed that the individuals of S. m. melanotheron subspecies from a much polluted environment (lagoon of Grand-Lahou or Ebrié) presented a relatively higher frequency of allele GPI-2*80 than those of a less polluted environment (Aby lagoon and Ayamé lake). The allele IDH-2*90 was expressed only in the specimens of S. m. heudelotii found in the Saloum estuary, a very saline environment compared to the estuary of Gambia. A deficit of heterozygosis was observed with the tilapia Sarotherodon melanotheron. This study confirmed the possibility of using allozymes as biomarkers and bioindicators of environmental disturbances.

Changes in gill ionocyte morphology and function following transfer from fresh to hypersaline waters in the tilapia Sarotherodon melanotheron

This is the first study concerning the effects of salinity on the gill ion secreting mechanisms of the black-chinned tilapia Sarotherodon melanotheron heudelotii originating from a hypersaline estuary (Saloum, Senegal). Under controlled conditions, juvenile fish initially kept in freshwater (FW) were divided into two groups exposed to FW or directly to 35 psu seawater (SW). Part of SW fish were then acclimatized to hypersaline waters (HW) by a step-wise increase of 7 psu/day up to 70 (HW70) and 90 psu (HW90). Three major ion transporters in gill ionocytes, Na +/K +-ATPase, the cotransporter Na +/K +/2Cl − (NKCC) and Cl − channel (CFTR) were localized by immunofluorescence and ionocyte localization, number and size were investigated. In FW, ionocytes immunostained with Na +/K +-ATPase were only observed at the base of the filaments, whereas in SW and particularly in HW they were localized on the filaments and expanded extensively to the lamellae, indicating the functional challenge that these fish encounter. A significant increase in ionocyte number and size (area) occurred following transfer from FW to SW and HW. Although the cell number remained constant between HW70 and HW90, their size increased from FW to HW90. The marked increase in cell number and size indicates that the cells are functioning at a high intensity in HW. In FW, Na +/K +-ATPase was concentrated at the basolateral region while NKCC staining was apical and CFTR was not observed. In SW and HW, Na +/K +-ATPase and the cotransporter NKCC were colocated on the basolateral membrane, while CFTR was located at the apical region. These findings agree with the literature on other chloride secreting cells, in which a relation between the location of the transporters and chloride secretion could be established.

Mutualism between euryhaline tilapia Sarotherodon melanotheron heudelotii and Chlorella sp.—Implications for nano-algal production in warmwater phytoplankton-based recirculating systems

The West-African euryhaline tilapia, Sarotherodon melanotheron heudelotii shift from visually feeding on zooplankton when juveniles to mostly filter feeding on phytoplankton when adults. When reared using an appropriate ration in intensive aquaculture systems, S. m. heudelotii also consume algal-based detritus, and contribute to sediment mineralization, clean up their environment, and ultimately stimulate and sustain algal growth. We analysed such practical advantages for phytoplankton-based recirculating systems, using S. m. heudelotii and Chlorella sp. as biological material originating from the prototype of such a system operated in Senegal. We performed a 24-h factorial design experiment in 36 tubs, cross-classifying three levels of S. m. heudelotii (fishless control, unfed fish, and fed fish) with four levels of Chlorella initial density. Chlorella overall mean density increased significantly from fishless, to unfed fish, and fed fish treatments, and with Chlorella initial density. S. m. heudelotii did not alter nitrogen nor phosphorus concentrations, only affected by algal initial densities. Most ammonia excreted by fish was probably uptaken by Chlorella. Bacteria-mediated diurnal nitrification was possibly an alternative ammonium loss mechanism at highest oxygen concentrations. Algae were not limited by nitrogen or phosphorus but most likely by low dissolved organic carbon availability. Chlorella differential responses with fed vs. unfed Sarotherodon suggest that CO 2 supplied by heterotrophic S. m. heudelotii respiration played a key role. Observed Chlorella growth rates were similar to the highest rates obtained in algal mass cultures, enriched with CO 2, nitrate and phosphate, under artificial lighting. Our results suggest the existence of a Sarotherodon-Chlorella mutualism in our systems, where S. m. heudelotii provide CO 2, the major limiting factor of Chlorella growth, whereas Chlorella oxygenate and detoxify the water media from ammonia, promoting S. m. heudelotii production. This mutualism could be used to optimize photosynthetic suspended-growth aquaculture systems, particularly in the Tropics where light is abundant and temperature is continuously high.

Changes in gill ionocyte function and structure following transfer from fresh to hypersaline waters in the tilapia Sarotherodon melanotheron

The effects of salinity were investigated in the black-chinned tilapia Sarotherodon melanotheron heudelotii originating from a hypersaline estuary (Saloum, Senegal). Under controlled conditions, juvenile fish originally kept in freshwater (FW) were divided into two groups exposed to FW or directly to 35 psu seawater (SW). Part of these SW fish were then acclimatised to hypersalinewaters (HW) by a step-wise increase of 7 psu/day up to 70 (HW70) and 90 (HW90). Three major ion transporters, Na+/K+-ATPase, the cotransporter Na+/ K+/2Cl- (NKCC) and the Cl- channel (CFTR) were localized by immunofluorescence in the gill ionocytes and changes regarding ionocytes localization, number and sizes were investigated. In FW, Na+/K+-ATPase immunostained ionocytes were only observed at the base of the filaments, whereas in SW and HW they were localized on both the filaments and the lamellae suggesting that lamellar ionocytes could also be functional in SW. A significant increase in ionocyte number and size (area) occurred following transfer from FW to HW. Although the cell number remained constant between HW70 and HW90, their size increased from FW to HW90, indicating that the size and shape of cells could be a sensitive indicator of osmoregulation in HWin this tilapia. In FW, NKCC stainingwas concentrated at the apical region and CFTR was not observed. In SW, Na+/K+-ATPase and the cotransporter NKCC were colocalized on the basolateral membrane, while CFTR was located at the apical region. (Resume d'auteur)