Effects of feeding rate and frequency on growth performance,digestion and nutrients balances of Atlantic salmon (Salmo salar) in recirculating aquaculture systems (RAS)

A 10‐week study was conducted to investigate the effects of feeding rate and frequency on growth performance, digestion and nutrients balances of Atlantic salmon (Salmo salar) in replicated recirculating aquaculture systems (RAS). Replicated groups of juvenile salmon weighing 90 ± 2.5 g (mean ± SD) were fed a commercial feed (21.63 MJ kg^?1 gross energy) to designed feeding rate (1.4%, 1.6% and 1.8% body weight day^?1, BW day^?1) and feeding frequency (2 and 4 meals day^?1) combinations. Specific growth ratio varied between 1.15 ± 0.02 and 1.37 ± 0.16% day^?1, and feed conversion ratio ranged from 0.96 ± 0.03 to 1.16 ± 0.02. The nitrogen and phosphorus retention rates were from 36.50 ± 1.94 to 47.08 ± 5.23% and from 20.42 ± 1.05 to 38.59 ± 2.80%. Apparent digestibility coefficients (ADC) in dry matter, protein, lipid and energy showed no significant differences for all groups. However, fish fed at 1.6% BW day^?1 and 4 meal day^?1 groups had relatively better growth and nutrient retention efficiency compared to other groups. In addition, concentrations of nitrogenous and phosphorous compounds were also detected in this study. These results suggested that salmon of 100–200 g in RAS could in practice be fed at 1.6% BW day^?1 and 4 meals day^?1, taking environmental impacts into account.     

The effect of density in larval rearing of the pullet carpet shell Venerupis corrugata (Gmelin, 1791) in a recirculating aquaculture system

The pullet carpet shell Venerupis corrugata is an economically valuable species in several European countries, however, nowadays stocks are under high fishing pressure. Hatchery production of juveniles for release is a major contributor to strengthen the stock and consequently improve the sustainability of the natural stocks. This study aimed to determine the feasibility of rearing V. corrugata larvae with different larval densities (10, 40 and 200 larvae per mL) in a recirculating aquaculture system (RAS), compared with the traditional larval rearing methodology (Batch). The mean survival, growth and metamorphic rate of V. corrugata larvae in RAS was higher (11.1%; 71.3 μm; 21.6% respectively) than in the Batch system, in all tested densities. The larval growth was not affected by the initial density until 40 larvae per mL, however, 200 larvae per mL decreased the larval growth in length nearly 54 μm. The larval rearing time was shortened in 2 days in the RAS system. The physical, chemical and microbiologic parameters suggested that the tested densities were not excessive to disturb the biofilter stability of RAS. The V. corrugata larval rearing performed at high larval stocking densities in RAS system present a reduction in the operating costs to produce this species.     

The South American freshwater fish Prochilodus lineatus (Actinopterygii: Characiformes: Prochilodontidae): new species in Vietnamese aquaculture

The freshwater characiform fish Prochilodus lineatus is a detritivorous species that has its native distribution area in South America but has been imported to China for aquaculture purposes. This is the first time that it is being reported in Vietnam, both from aquaculture and captured from a river channel. According to local authorities, the species is becoming increasingly important in local aquaculture and its spread can be expected. Keeping in mind the high biomass production in the rivers of its native distribution area, a successful establishment of P. lineatus into Vietnamese fresh waters may exert serious impacts on the local ecosystems.     

Effects of rearing density on growth,fatty acid profile and bioremediation ability of polychaete Nereis diversicolor in an integrated aquaculture system with rainbow trout (Oncorhynchus mykiss)

The objective of this study was to assess the effects of rearing density on the growth and fatty acid profile of Nereis diversicolor and on its capability to bioremediate wastewater in an integrated culture system with rainbow trout (Oncorhynchus mykiss). To this end, a batch of juvenile N. diversicolor (0.03 ± 0.01 mg) was assigned into four different densities (T₁ = 250, T₂ = 500, T₃ = 1,000, T₄ = 2,000, besides T₀ = with no worm) in three replicates. The worm groups were fed with solid waste that was supplied from tanks containing rainbow trout (107.17 ± 13.5 g; 1.39 ± 0.18 kg/m³). During the experiment (60 days), the water temperature was 17.71 ± 0.6°C. The results revealed that SR%, SGR% and WG% of N. diversicolor in T₁ were significantly higher than those of T₂, T₃ and T₄. Both FER rate and biomass gain in T₄ were significantly higher than those in the other groups. The highest removal rate of NO₂‐N (73.72%), NH₃‐N (65.70%), PO₄‐P (59.32%), BOD₅ (69.60%) and TSS (82.33%) were observed in T₄. The major fatty acids presents were palmitic acid, oleic acid, linoleic acid, stearic acid and alpha‐linolenic acid in all worm‐treated groups, with no difference observed in the concentration of these fatty acids among them. Taken together, these findings suggest that organic wastes from rainbow trout farms could be recycled to achieve a sustainable aquaculture goal, and demonstrate that a high percentage of fatty acids in fish feed is not absorbed by rainbow trout but is done by N. diversicolor.     

Use of essential oils extracted from three Origanum species for disinfection of cultured rotifers (Brachionus plicatilis)

Essential oils extracted from three plant species of the genus Origanum, Origanum vulgare subsp. hirtum, Origanum onites L. and Origanum marjorana L., were assayed as potential antibacterial agents for disinfection of rotifers Brachionus plicatilis. Survival of rotifers in seawater with added oregano essential oils was significantly higher than in the control treatment (P < 0.05). When rotifers were incubated in seawater with added oregano essential oils at a final concentration of 10 mg L^?1 for 4 h, the numbers of total culturable bacteria were not significantly lower than in the control treatment (P > 0.05), while the numbers of presumptive Vibrio in rotifers were significantly reduced compared with the control treatment (P < 0.05).     

Influence of social factors on the nocturnal activity pattern of the noble crayfish,Astacus astacus (Crustacea,Decapoda) in recirculating aquaculture systems

The social environment plays a major role in the control of growth in many crustaceans, but little is known on the mechanisms involved. Two‐ and three‐year‐old noble crayfish, Astacus astacus are strictly nocturnally active. In the present article, we studied social effects on the pattern of nocturnal activity, represented by the time which the animals spent outside shelters. For this purpose, the activity of groups of uniformly large (‘dominant’) and uniformly small (‘subordinate’) individuals were recorded at different densities both separately and in mixed set‐ups. In crowded laboratory cultures, the presence of larger (dominant) conspecifics was found to reduce the time which smaller (subordinate) individuals spent outside shelters in search of food and feeding by about one‐third. It is suggested that this asymmetric inhibitory effect is an element of the functional chain which ultimately results in an extremely wide variation in individual growth rates of communally reared A. astacus. The relevance of the findings to crayfish aquaculture is discussed.     

One cryptic species of grey mullet (Mugil cephalus mitotype: NWP3) from Taiwan’s waters is worth cultivating for large roes using aquaculture

The grey mullet, Mugil cephalus, is an important aquaculture species in Taiwan. They were thought to be a single fish species in terms of the morphology‐based taxonomy; however, three cryptic species of grey mullet (mitotype: NWP1, NWP2 and NWP3) have been identified within the Taiwan waters. In general, the NWP2 females are known to have small body sizes with large developed ovaries regardless of the cultivation time, whereas the NWP1 females have large body sizes with small ovaries. In this study, the NWP3 females are found to have significantly larger body and ovary weights than do the NWP2 females under the same aquaculture conditions. Therefore, even though the NWP2 females are good fish for producing large ovaries, this study indicates that the NWP3 females have even more potential to produce huge ovaries than do the NWP2 females.     

Survival,growth and biomass of mud polychaete Marphysa iloiloensis (Annelida: Eunicidae) under different culture techniques

Polychaetes are commercially exploited as fishing bait and supplemental diet to crustacean and finfish broodstock. However, scarcity of supply and biosecurity issues limits its use. Polychaete aquaculture has become the best alternative to wild resources. In this study, two different culture techniques (1‐sediment tank throughout the culture period and 2‐nursery tank with bioflocs for 30 days; thereafter, juveniles were transferred to sediment tank until harvest) using two diets [bioflocs (BF) and feed mill sweepings (FS)] were tested to determine the survival, growth and biomass of polychaete Marphysa iloiloensis (Glasby et al., Zootaxa, 2019, 4674) in the grow‐out. The 180‐day trial was conducted in 16 tanks (0.20 m²) stocked with 5,066 ± 575 M. iloiloensis trochophore larvae/tank which were assigned randomly into four culture treatments with four replicates each. The treatments were labelled as: (a) BFS – fed BF in sediment tank for 180 days; (b) BF + BFS – fed BF in nursery tank for 30 days, juveniles were transferred in sediment tank and fed BF for another 150 days; (c) FSS – fed FS in sediment tank for 180 days; and (d) BF + FSS – fed BF in nursery tank for 30 days, juveniles are transferred in sediment tank and fed FS for another 150 days. Results showed that polychaetes in BF + FSS had significantly higher survival than BFS. Polychaetes in both BF + FSS and FSS had significantly higher body weight than BF + BFS and BFS, while biomass in BF + FSS (175.73 ± 42.25 g/tank) was significantly higher compared to other treatments (p < .05). Polychaetes fed with FS had 61%–64% protein and 12%–13% fat, while those fed with BF exclusively had 66%–70% protein and 3.50%–4.50% fat. The findings indicate that FS whether or not BF is included in the diet can improve both survival and growth of polychaetes but significantly higher biomass can be achieved with the combination of BF and FS. Additionally, polychaetes in BF + FSS contained 64% protein and 13% fat. Therefore, BF can be used as an alternative diet to FS in the early life stages of M. iloiloensis and nursery rearing using BF is imperative to increase its biomass in the grow‐out production.     

Total nitrogen,carbon and phosphorus digestibility in gilthead seabream (Sparus aurata) and European seabass (Dicentrarchus labrax) fed with conventional and organic commercial feeds: implications for particulate waste production

Organic fish farming is postulated as a more environmentally friendly activity than conventional activities. However, environmental sustainability as regards waste output has not been addressed. In this respect, the most important environmental problems associated with fish farming are those related with the discharge of particulate wastes. In this study, total nitrogen, carbon and phosphorus digestibility was estimated in a wide size range of gilthead seabream (Sparus aurata) and European seabass (Dicentrarchus labrax) fed a commercially available conventional diet and an organic feed, as a previous step to assessing particulate waste output. Neither fish size nor feed nutrient content was seen to influence nutrient digestibility in either species. The organic diet provided higher carbon but lower nitrogen and phosphorus digestibility than conventional feed in both species. Simulations under real ongrowing conditions resulted in lower values for nitrogen and higher values for carbon particulate wastes when conventional feed was supplied to both species. Particulate phosphorus wastes were 2.6‐ to 3.4‐fold higher for fish fed the organic diet. Restrictions concerning NO the raw materials used for organic diet formulation and differences in nutrient bioavailability between the diets seemed to be the underlying reason for the differences found.     

Effects of feeding rates on the growth,water quality and nutrient budget of western king prawn (Penaeus latisulcatus Kishinouye) reared in recirculating aquaculture systems

Feed rate is one of the important variables considered for the improvement in production of prawns. The effects of four feeding rates on growth, water quality and the nutrient budget of Penaeus latisulcatus were investigated for 98 days. The specific growth rate (SGR) at 3.0% feed rate was significantly higher than at all higher feed rates, and there was no significant difference in SGR between 4.5%, 6% and 7.5%. Total ammonia nitrogen concentrations in all treatments remained low in the safe range for prawn culture. Dissolved inorganic nitrogen and nitrate nitrogen were significantly higher (P < 0.05) in prawn tanks received feed rates of 6.0% and 7.5%. Total phosphorus and the soluble reactive phosphorus linearly increased with the progression of the trial and feeding rates. Nutrient conversion rates were significantly higher (P < 0.05) in prawns receiving the feeding rate of 3.0% than feeding rates of 6.0% and 7.5%. The lowest food conversion ratio was recorded at feeding rates of 3% and 4.5%. Nutrient budget showed that 6.01–15.99% nitrogen and 4.53–9.29% phosphorus of the nutrient inputs were retained in the prawn biomass. The results indicated that the growth and nutrient conversion rate may not increase with the increase above 3.0% of biomass per day.     

Evaluation and characterization of a novel probiotic Lactobacillus pentosus PL11 isolated from Japanese eel (Anguilla japonica) for its use in aquaculture

In the present study, a potential Lactobacilli probiotics were isolated from Japanese eels (Anguilla japonica) and characterized and evaluated for their possible use in eel farming. Sixteen Lactobacilli were isolated from intestines of Japanese eels, using selective media. The lactobacilli strains (represented as PL1 to PL16) were screened by their ability to produce digestive enzyme. Among these, three strains (PL11, PL13 and PL16) producing four digestive enzymes (amylase, cellulase, protease and phytase) simultaneously were characterized further using API ZYM kit. From these, PL11 (Lactobacillu (L.) pentosus) was identified as potential probiotics candidate producing 15 enzymes among 20 tested. Further examination of biological activities of PL11 revealed tolerance against pH, artificial bile juice and antibacterial activity against several fish pathogenic bacteria. The in vitro competitive exclusion assay also revealed 88.4% reduction in adhesion of fish pathogen (Edwardsiella tarda) by PL11 to host intestinal mucus. In vitro incubation of Japanese eel foregut with Baclight‐labelled PL11 showed colonization of the enterocyte surface by confocal and scanning electron microscopy. In summary, PL11 isolated from eels could serve as a potential probiotics with acid and bile tolerance, production of digestive enzymes, antibacterial activity and inhibition of fish pathogen adhesion to intestinal mucus.     

The role of polychaete Nereis diversicolor in bioremediation of wastewater and its growth performance and fatty acid composition in an integrated culture system with Huso huso (Linnaeus, 1758)

This study was undertaken to evaluate the role of polychaete Nereis diversicolor in bioremediation of waste water and its growth performance and fatty acid composition in an integrated culture system with great sturgeon, Huso huso. Three treatments consisting of N. diversicolor fed with H. huso waste (FNW), N. diversicolor fed with fish feed waste (NW), and fish waste without the worm (FW) were considered at water temperature of 23°C for 8 weeks. The obtained results demonstrated that N. diversicolor in the flow‐through system could grow via feeding with the fish waste water. The pure production and survival rate of harvested Nereis in NW treatment were significantly higher than those of FNW treatment (p < .05). However, no significant difference was observed in specific growth rate and weight gain between these two treatments (p > .05). The highest removal efficiency of waste water including total nitrogen (56%), total phosphorus (53%), NO₂‐N (91%), NH₃‐N (35%)_, PO₄‐P (47%), BOD₅ (60%) were seen in FNW treatment. Also, the highest additional efficiency of NO₃‐N occurred in FW (37%) treatment. Certain fatty acids specifically 20:5 ω3 (eicosapentaenoic acid [EPA]) and 22:6 ω6 (docosahexaenoic acid [DHA]) were also abundant in Nereis, and analysis revealed some differences due to the diet. These results demonstrated that the promotion of growth by cultured Nereis can enhance the decomposition rate of organic matter in enriched sediment and minimize negative effects in fish farms. These results also suggest that the use of N. diversicolor is an excellent potential candidate for an integrated aquaculture and nutrient recycling including the removal of organic wastes.     

Growth variations within a farm of mussel (Mytilus galloprovincialis) held near fish cages: importance for the implementation of integrated aquaculture

Fish farming releases extensive amounts of particulate organic waste that can be exploited by bivalves in integrated culture. We tested if mussels Mytilus galloprovincialis cultured at two depths (1 and 6 m) in a raft, moored 170 m from a fish farm had greater growth than bivalves held 550 m from the fish cages. Mussel growth was monitored monthly, covering the second phase of the culture, from thinning‐out to harvest (March to November 2011). We also studied if fish solid and dissolved nutrients increased the organic content of the seston and chlorophyll‐a levels near the fish cages through weekly samples. Results showed no differences in seston, chlorophyll and physiochemical characteristics of the water among rafts. Maximum growth and Condition Index (CI) occurred during spring–summer (April–August), when mussels had access to greater food quality and quantity. Mussels cultivated close to the cages showed similar shell length, weight and CI compared with mussels distant from the fish farm. Average shell length, meat dry weight and CI at harvest were 76.31 mm, 2.51 g and 23%. Bivalves cultured distant from the fish cages displayed 26% higher biomass than the other raft at the end of the experiment. Differences in biomass were explained by the significantly higher recruitment of mussel seed observed at the raft distant from the fish cages from June to November. The lack of a significant enhancement in growth of the bivalves cultured next to finfish is discussed.     

PCR survey for Paramoeba perurans in fauna,environmental samples and fish associated with marine farming sites for Atlantic salmon (Salmo salar L.)

Amoebic gill disease (AGD) caused by the amoeba Paramoeba perurans is an increasing problem in Atlantic salmon aquaculture. In the present PCR survey, the focus was to identify reservoir species or environmental samples where P. perurans could be present throughout the year, regardless of the infection status in farmed Atlantic salmon. A total of 1200 samples were collected at or in the proximity to farming sites with AGD, or with history of AGD, and analysed for the presence of P. perurans. No results supported biofouling organisms, salmon lice, biofilm or sediment to maintain P. perurans. However, during clinical AGD in Atlantic salmon, the amoeba were detected in several samples, including water, biofilm, plankton, several filter feeders and wild fish. It is likely that some of these samples were positive as a result of the continuous exposure through water. Positive wild fish may contribute to the spread of P. perurans. Cleaner fish tested positive for P. perurans when salmon tested negative, indicating that they may withhold the amoeba longer than salmon. The results demonstrate the high infection pressure produced from an AGD‐afflicted Atlantic salmon population and thus the importance of early intervention to reduce infection pressure and horizontal spread of P. perurans within farms.     

Impact of sublethal di‐n‐butyl phthalate on the aquaculture fish species Nile tilapia (Oreochromis niloticus): histopathology and oxidative stress assessment

Phthalates such as di‐n‐butyl phthalate (DBP) and their esters are widely used plasticizers, their ubiquitous presence in daily life, inevitably leads to their restricted use due to important environmental pollution and health impacts and endocrine disruption potential. The aim of this study was to examine the effects of a sublethal concentration of 10 mg L^?1 DBP on haematocrit (HCT) values, gills and liver histology, malondialdehyde (MDA, 2‐thiobarbituric acid‐TBA reactivity) and reduced glutathione (GSH) levels in gills and liver tissue as oxidative stress biomarkers in the aquaculture fish species Nile tilapia (Oreochromis niloticus) after 24 (DBP‐24) and 96 (DBP‐96) h exposure. No differences were found between per cent HCT values in the 24 h exposure groups (P > 0.05). Response of antioxidant defence systems in liver and gill tissues of the fish were dependent on exposure duration and changed to a higher extent during 96 h. MDA levels in liver tissue increased in DBP treated fish in comparison to the control fish. However, the differences between the exposure and control groups were not significant (P > 0.05). A statistically significant decrease (P > 0.05) was recorded in gill MDA levels in the DBP‐96 group when compared to the control and DBP‐24 groups. The liver GSH levels were unchanged in the DBP treated fish. However, GSH levels were significantly lower in the gill tissue of the DBP‐96 group. Exposure to DBP caused several degenerative changes in the histology of gill and liver tissue. Gills displayed hyperaemia, epithelial lifting, oedema, talengiectasia, epithelial hyperplasia and fusion of secondary lamellae, whereas in liver several circulatory anomalies (hyperaemia, blood congestion and sinosoid dilatation) and vacuolization of hepatocytes were observed. Histopathological results demonstrated that the gills were more affected than the liver perhaps due to their direct contact with DBP.     

A comparison between marine and terrestrial invertebrate meals for mirror carp (Cyprinus carpio) diets: Impact on growth,haematology and health

Invertebrate meals (e.g. polychaetes and insects) present novel and sustainable high‐quality nutrient sources for use in fish feed formulations. To test this innovative source, an eleven‐week feeding trial was conducted evaluating the effects of replacing the fishmeal (FM) component as an example of a superior protein source (FM CTRL) with ragworm meal (RW, Nereis virens) and/or silkworm pupae (SWP, Bombyx mori) in mirror carp (Cyprinus carpio) diets. Three experimental diets with partial replacement of FM (diets: RW + FM, SWP + FM and RW + SWP + FM) were formulated. All diets were formulated to be iso‐nitrogenous, iso‐lipidic and iso‐energetic. Growth performance and feed utilization indices were assessed, and the feeding trial concluded with the analysis of haematological parameters to provide an indication of carp physiological and health status. Mean weight gain was greatest in mirror carp fed RW + FM (60.83 fish^?1 day^?1; P < 0.05 vs. all other diets) followed by SWP + FM (40.62 g fish^?1 day^?1; P < 0.05 vs. all other diets). The least weight gain was achieved in fish fed FM + SWP + RW+ and FM CTRL (34.34 and 33.96 g fish^?1 day^?1, respectively; not significantly different from each other). Fish fed on RW + FM diet had significantly lower plasma ammonia concentrations than any other dietary groups (P = 0.04). Mirror carp fed on SWP + FM diet (111.52 units mL^?1) were observed to have a marked enhancement in alternative complement activity than FM CTRL (79.21 units mL^?1, P = 0.041). Both ragworm and silkworm pupae meal present attractive sustainable functional feed component in carp diets, with benefits on enhancing growth performance and specific physiological parameters.     

Morphological and genetic characterization of Hysterothylacium Ward & Magath, 1917 (Nematoda: Raphidascarididae) larvae in horse mackerel,blue whiting and anchovy from Spanish Atlantic and Mediterranean waters

The presence of zoonotic Hysterothylacium larvae in fish from Spanish Atlantic and Mediterranean waters, which can cause economic losses for commercial fisheries, has been reported in several studies; however, little is known about species identity in this region. The aim of this study was to identify at species level the Hysterothylacium morphotypes detected in three commonly consumed fish: horse mackerel (Trachurus trachurus), blue whiting (Micromesistius poutassou) and anchovy (Engraulis encrasicolus). Third‐ and fourth‐stage Hysterothylacium larvae, as well as adults obtained from larval in vitro culture, were morphologically and molecularly identified by ITS1/ITS2 rDNA sequencing. Four Hysterothylacium morphotypes were detected. Genetic analysis showed that morphotypes VIII and IX were different larval stages of Hysterothylacium aduncum, which was supported by cultured adult species identification. Morphotypes III and IV were found to correspond to different developmental stages of another species of Hysterothylacium. As all larval types detected were morphologically indistinguishable from others previously reported yet showed clear genetic differences, they are referred here as new genotypes. This is the first time that ITS‐sequence data of various developmental stages of the same species, including adults, have been studied and compared, providing crucial knowledge for future studies on Hysterothylacium identification and biology.