Influence of Substrates on the Quality of Hermetia Meal for Fish Meal Substitution in Nile Tilapia Oreochromis niloticus

Commercially produced black soldier flies (Hermetia illucens) represent a promising fish meal substitute, particularly in the context of using agricultural by-products and waste. Here, the culture of Hermetia maggots on five selected substrates (potato protein (P) as a by-product of starch production, rapeseed oil cake (R) from rape oil production, maize silage (M), soybean (S) meal and, as a control, concentrated chicken feed (C)) were evaluated, assessing the growth performance of Hermetia maggots related to the overall production and the nutritional composition of the respective meal. Subsequently, their use as ingredients in aquafeed formulations was evaluated in a feeding trial with juvenile Nile tilapia Oreochromis niloticus, assessing the growth performance of the fish. Substrates used for Hermetia culture significantly affected the growth and development of the maggots, revealing substantial differences in the meal quality. Still, if incorporated in isonitrogenous and isocaloric diets (33% crude protein, 21–22 MJ/kg) replacing 75% of the fishmeal protein in the formulated diets, no significant differences in growth performance of the fish were observed compared to the fishmeal control. As a conclusion, substrates clearly affect the production yield and the composition of maggots. Nevertheless, this can be compensated by feed formulation as demonstrated by the feeding trial.Peer Reviewe

Two Probiotic Candidates of the Genus Psychrobacter Modulate the Immune Response and Disease Resistance after Experimental Infection in Turbot (Scophthalmus maximus, Linnaeus 1758)

Probiotic bacteria are a recognized alternative to classical methods of disease prophylaxis and therapy. We tested the effects of their application on the immune reaction in juvenile turbot. To prevent digestion of the probiotics, rectal administration was applied to maximise colonization, by-passing digestion in the stomach. The application of Psychrobacter nivimaris and Psychrobacter faecalis showed beneficial effects on the inflammatory response and disease resistance after infection with the common pathogen Tenacibaculum maritimum. Treatment with P. nivimaris and P. faecalis resulted in 0% and 8% mortalities post-infection, while in the treatment control, an elevated mortality of 20% was observed. In the challenge controls (no infection), no mortalities were observed during the entire experimental period. After an experimental infection, mRNA expression of selected immune markers (mhc II α, il-1β, tcr, tgf β and tnf α) were determined by RT-QPCR at 0, 1 and 5 days post-infection (dpi). At 0 dpi, gene expression was comparable between the treatments and the treatment control, suggesting that probiotics did not act via immune stimulation of the host. At 1 dpi, all genes were up-regulated in the treatment control but not in the probiotic groups, indicating that the infection in probiotic-treated fish developed at a less severe level. At 5 dpi, mRNA expression returned to baseline levels. As a conclusion, the native probiotic candidates P. nivimaris and P. faecalis improved survival, whereas, in the control, mortality increased and expression of the immune markers was up-regulated post infection. This highlights a potential application of P. nivimaris and P. faecalis in disease prophylaxis, but further research is needed.FCT/DAAD Acções Integradas Luso-AlemãsFCT/DAAD Acções Integradas Luso-AlemãsFCTFCTFCTERASMUS+ Traineeship Programme of the European UnionPeer Reviewe

Navigating towards decoupled aquaponic systems : a system dynamics design approach

The classical working principle of aquaponics is to provide nutrient-rich aquacultural water to a hydroponic plant culture unit, which in turn depurates the water that is returned to the aquaculture tanks. A known drawback is that a compromise away from optimal growing conditions for plants and fish must be achieved to produce both crops and fish in the same environmental conditions. The objective of this study was to develop a theoretical concept of a decoupled aquaponic system (DAPS), and predict water, nutrient (N and P), fish, sludge, and plant levels. This has been approached by developing a dynamic aquaponic system model, using inputs from data found in literature covering the fields of aquaculture, hydroponics, and sludge treatment. The outputs from the model showed the dependency of aquacultural water quality on the hydroponic evapotranspiration rate. This result can be explained by the fact that DAPS is based on one-way flows. These one-way flows results in accumulations of remineralized nutrients in the hydroponic component ensuring optimal conditions for the plants. The study also suggests to size the cultivation area based on P availability in the hydroponic component as P is an exhaustible resource and has been identified one of the main limiting factors for plant growth

Diversity of immunoglobulin light chain genes in non-teleost ray-finned fish uncovers IgL subdivision into five ancient isotypes

<p>The aim of this study was to fill important gaps in the evolutionary history of immunoglobulins by examining the structure and diversity of IgL genes in non-teleost ray-finned fish. First, based on the bioinformatic analysis of recent transcriptomic and genomic resources, we experimentally characterized the IgL genes in the chondrostean fish, Acipenser ruthenus (sterlet). We show that this species has three loci encoding IgL kappa-like chains with a translocon-type gene organization and a single VJC cluster, encoding homogeneous lambda-like light chain. In addition, sterlet possesses sigma-like VL and J-CL genes, which are transcribed separately and both encode protein products with cleavable leader peptides. The Acipenseriformes IgL dataset was extended by the sequences mined in the databases of species belonging to other non-teleost lineages of ray-finned fish: Holostei and Polypteriformes. Inclusion of these new data into phylogenetic analysis showed a clear subdivision of IgL chains into five groups. The isotype described previously as the teleostean IgL lambda turned out to be a kappa and lambda chain paralog that emerged before the radiation of ray-finned fish. We designate this isotype as lambda-2. The phylogeny also showed that sigma-2 IgL chains initially regarded as specific for cartilaginous fish are present in holosteans, polypterids, and even in turtles. We conclude that there were five ancient IgL isotypes, which evolved differentially in various lineages of jawed vertebrates.</p

Neuroendocrine and Immune Responses Undertake Different Fates following Tryptophan or Methionine Dietary Treatment: Tales from a Teleost Model

Methionine and tryptophan appear to be fundamental in specific cellular pathways involved in the immune response mechanisms, including stimulation of T-regulatory cells by tryptophan metabolites or pro-inflammatory effects upon methionine supplementation. Thus, the aim of this study was to evaluate the immunomodulatory effect of these amino acids on the inflammatory and neuroendocrine responses in juveniles of European seabass, Dicentrarchus labrax. To achieve this, goal fish were fed for 14 days methionine and tryptophan-supplemented diets (MET and TRP, respectively, 2× dietary requirement level) or a control diet meeting the amino acids requirement levels (CTRL). Fish were sampled for immune status assessment and the remaining fish were challenged with intraperitoneally injected inactivated Photobacterium damselae subsp. piscicida and sampled either 4 or 24 h post-injection. Respiratory burst activity, brain monoamines, plasma cortisol, and immune-related gene expression showed distinct and sometimes opposite patterns regarding the effects of dietary amino acids. While neuroendocrine intermediates were not affected by any dietary treatment at the end of the feeding trial, both supplemented diets led to increased levels of plasma cortisol after the inflammatory insult, while brain monoamine content was higher in TRP-fed fish. Peripheral blood respiratory burst was higher in TRP-fed fish injected with the bacteria inoculum but only compared to those fed MET. However, no changes were detected in total antioxidant capacity. Complement factor 3 was upregulated in MET-fed fish but methionine seemed to poorly affect other genes expression patterns. In contrast, fish fed MET showed increased immune cells numbers both before and after immune challenge, suggesting a strong enhancing effect of methionine on immune cells proliferation. Differently, tryptophan effects on inflammatory transcripts suggested an inhibitory mode of action. This, together with a high production of brain monoamine and cortisol levels, suggests that tryptophan might mediate regulatory mechanisms of neuroendocrine and immune systems cooperation. Overall, more studies are needed to ascertain the role of methionine and tryptophan in modulating (stimulate or regulate) fish immune and neuroendocrine responses

Probiotics in Fish Nutrition—Long-Standing Household Remedy or Native Nutraceuticals?

Over the last decades, aquaculture production increased rapidly. The future development of the industry highly relies on the sustainable utilization of natural resources. The need for improving disease resistance, growth performance, food conversion, and product safety for human consumption has stimulated the application of probiotics in aquaculture. Probiotics increase growth and feed conversion, improve health status, raise disease resistance, decrease stress susceptibility, and improve general vigor. Currently, most probiotics still originate from terrestrial sources rather than fish. However, host-associated (autochthonous) probiotics are likely more persistent in the gastrointestinal tract of fish and may, therefore, exhibit longer-lasting effects on the host. Probiotic candidates are commonly screened in in vitro assays, but the transfer to in vivo assessment is often problematic. In conclusion, modulation of the host-associated microbiome by the use of complex probiotics is promising, but a solid understanding of the interactions involved is only in its infancy and requires further research. Probiotics could be used to explore novel ingredients such as chitin-rich insect meal, which cannot be digested by the fish host alone. Most importantly, probiotics offer the opportunity to improve stress and disease resistance, which is among the most pressing problems in aquaculture.Peer Reviewe

Is Growth Inhibition in Regulated by Chemical Communication?

Due to high consumer demand for freshwater crustaceans, rearing technology is evolving towards intensive aquaculture. High stocking densities in such cultures result in close proximity of individuals. In this trial, we studied chemical communication and growth inhibition in order to clarify whether large males inhibit the growth of juveniles in Redclaw crayfish (Cherax quadricarinatus). No growth inhibition was observed in juveniles grown in the rearing water of adults. The experimental design can be modified to test behavioural and visual cues that may also interfere with juvenile growth

Decoupled systems on trial: Eliminating bottlenecks to improve aquaponic processes

In classical aquaponics (coupled aquaponic systems, 1-loop systems) the production of fish in recirculating aquaculture systems (RAS) and plants in hydroponics are combined in a single loop, entailing systemic compromises on the optimal production parameters (e.g. pH). Recently presented decoupled aquaponics (2-loop systems) have been awarded for eliminating major bottlenecks. In a pilot study, production in an innovative decoupled aquaponic system was compared with a coupled system and, as a control, a conventional RAS, assessing growth parameters of fish (FCR, SGR) and plants over an experimental period of 5 months. Soluble nutrients (NO3--N, NO2--N, NH4+-N, PO43-, K+, Ca2+, Mg2+, SO42-, Cl2- and Fe2+), elemental composition of plants, fish and sludge (N, P, K, Ca, Mg, Na, C), abiotic factors (temperature, pH, oxygen, and conductivity), fertilizer and water consumption were determined. Fruit yield was 36% higher in decoupled aquaponics and pH and fertilizer management was more effective, whereas fish production was comparable in both systems. The results of this pilot study clearly illustrate the main advantages of decoupled, two-loop aquaponics and demonstrate how bottlenecks commonly encountered in coupled aquaponics can be managed to promote application in aquaculture

Influence of rearing temperature and hormone treatment on sperm motility in burbot (Lota lota)

The burbot (Lota lota) has potential for freshwater aquaculture production. Burbot is a gadoid fish with a preference for cold temperatures and may therefore be suitable for species diversification. Still, the rearing conditions for reproduction and ongrowing are poorly understood. Burbot reproduce during the winter, require constant cold temperatures for spawning (McPhail and Paragamian, 2000) and undergo dramatic metabolic changes during this season in order to respond to energetic demands for reproduction (Mustonen et al. 2002). Knowledge of these processes is hence a necessary prerequisite to successfully establish Burbot in aquaculture. In other temperate species like pikeperch (Sander lucioperca), it was shown that temperature has a significant impact on the hormones involved in reproduction and spawning (Hermelink et al. 2011). These sensitive interactions may be strongly disturbed by environmental conditions and stress. There is a current lack of understanding with regards to how/if such a disturbance may affect the sperm performance and subsequent fertilization success. This study focuses on the effect of hormone treatment with Buserilin, as well as the impact of rearing temperature on the activation success of Burbot sperm.status: publishe

Lead-induced heat shock protein (HSP70) and metallothionein (MT) gene expression in the embryos of African catfish Clarias gariepinus (Burchell, 1822)

The enhanced expression of heat shock proteins (HSPs) and metallothionein (MT) can be detected in response to many environmental stressors, including exposure to heavy metals. We identified partial mRNA sequences for beta2-microglobulin (ß2m), heat shock cognate 70 kDa protein (HSP70), and MT in embryos of the African catfish Clarias gariepinus (Burchell, 1822). Levels of these transcripts were assessed using reverse-transcription quantitative polymerase chain reaction (RT-QPCR) after embryos of various stages were exposed to different concentrations of lead nitrate. ß2m gene expression exhibited a continuous increase over time. Neither HSP70 nor MT were upregulated, supporting the well-known sensitivity of these organisms to environmental pollutants. Interestingly, the partial MT and HSP70 mRNA sequences revealed an intimate phylogenetic relationship with these proteins in siluriforms. These partial sequences were more closely related to salmoniform proteins than to cypriniform proteins. The expression levels of HSP70 and MT were lower in embryonic tissues exposed to high concentrations of lead (500 µg/L), which impaired the fish's coping strategy via toxication at the cellular level. In conclusion, early developmental stages appear to be particularly vulnerable to lead and fail to activate the typical coping mechanisms. Therefore, these early life stages may not be suitable to characterize concentration-dependent toxicity. Keywords: Expression of stress proteins, RT-QPCR, Fish embryos, Heavy metal pollutio