Prevalence of nematode parasite,Contracaecum, in Nile tilapia,African catfish and Barbus species in Lake Hawassa,Ethiopia

A cross‐sectional study was conducted from November 2017 to March 2018 at Lake Hawassa to determine the prevalence of larval Contracaecum infestation in Nile tilapia, (Oreochromis niloticus), African Catfish (Clarias gariepinus) and Barbus species (Barbus intermedius). Fifty‐two point six per cent (52.6%) previous prevalence and 5% precision were used to estimate the sample size. Accordingly, a total of 383 randomly sampled fish species comprising of 163 (42.6%) C. gariepinus, 159 (41.5%) O. niloticus and 61(15.9%) B. intermedius were examined. The length and weight of each sampled fish were recorded. All the sampled fish were examined for the evidence of Contracaecum parasites in Hawassa University Veterinary Parasitology and Pathology Laboratory. Chi‐square values and comparison of proportions were used to analyse the data. The overall prevalence of Contracaecum parasites of fish population was 31.6%. The distribution of parasite was significantly affected by fish species (p = .000), sexes (p = .018), length (p = .003) and weight classes of fish (p = .026). As a hygienic problem and gutting activity conducted at the sides of the Lake Hawassa and distribution of discarded fish wastes for surrounding piscivorous birds by butchers and other people, the life cycle of Contracaecum parasite was perpetuated. Thus, the parasite is of zoonotic significance. Therefore, awareness creation activities for societies and control of fish parasites should be conducted in the study area.     

Parasitic infection of Cobitis elongatoides Băcescu & Mayer, 1969 by zoonotic metacercariae Clinostomum complanatum (Rudolphi, 1814)

An infection of zoonotic Clinostomum complanatum metacercariae with potential human transmission was recorded close to fish farms in the Tisa River Basin of Slovakia and Ukraine. The prevalence varied from 19.4% to 81.3%, and the intensity of infection varied from 7 to 41. The results of a generalized linear model predicted a positive trend for the Cobitis elongatoides host and a standard length and intensity of infection, with females having a higher number of parasites. However, no significant impact was found of the intensity of infection on Clark's condition of the host. The metacercariae were primarily located in the anterior part of the host's body. Our study also showed significant evidence that water velocity affects the number of C. complanatum metacercariae, regardless of the host's (Cobitis) microhabitat.     

Impact of polyculture ecosystems of Ctenopharyngodon idellus with Eriocheir sinensis on bacterial communities in the sediments of Dongping Lake in China: Focus on optimization of polyculture modes

This study investigated the influence of polyculture ecosystems of grass carp (Ctenopharyngodon idellus) and Chinese mitten crab (Eriocheir sinensis) on the bacterial community of sediments in the Lake Dongping in China, using the Illumina HiSeq Sequencing approach. The bacterial community diversity was reduced to different extent due to the polyculture of animals. The bacterial community composition changed significantly among the ecosystems of control (without any animals cultured), G1C1 (with the highest animal biomass: C. idellus, 2 ind/m²; E. sinensis, 1 ind/m²) and G2C2 (with the lowest biomass: C. idellus, 1 ind/m²; E. sinensis, 0.5 ind/m²). Relative abundance increase for sulphide‐oxidizing bacteria and decrease for sulphate‐reducing bacteria were detected with more quantities of fish–crab cultured in ecosystems. Variations in the concentration of sediment sulphate mainly accounted for the shifts of both the bacterial diversity and community composition. Lastly, G2C2 was recommended as the optimal polyculture ecosystem that could be used in the Lake. The results suggested negative impacts of polyculture ecosystems of C. idellus with E. sinensis on the bacterial diversity but positive impacts on the community composition and indicated the role of total biomass of animas in shaping the bacterial community in the sediments of lake ecosystems.     

Detection of tilapia lake virus (TiLV) infection by PCR in farmed and wild Nile tilapia (Oreochromis niloticus) from Lake Victoria

Tilapia lake virus disease (TiLVD) has emerged to be an important viral disease of farmed Nile tilapia (Oreochromis niloticus) having the potential to impede expansion of aquaculture production. There is a need for rapid diagnostic tools to identify infected fish to limit the spread in individual farms. We report the first detection of TiLV infection by PCR in farmed and wild Nile tilapia from Lake Victoria. There was no difference in prevalence between farmed and wild fish samples (p = .65), and of the 442 samples examined from 191 fish, 28 were positive for TiLV by PCR. In terms of tissue distribution, the head kidney (7.69%, N = 65) and spleen (10.99%, N = 191), samples had the highest prevalence (p < .0028) followed by heart samples (3.45%, N = 29). Conversely, the prevalence was low in the liver (0.71%, N = 140) and absent in brain samples (0.0%, N = 17), which have previously been shown to be target organs during acute infections. Phylogenetic analysis showed homology between our sequences and those from recent outbreaks in Israel and Thailand. Given that these findings were based on nucleic acid detection by PCR, future studies should seek to isolate the virus from fish in Lake Victoria and show its ability to cause disease and virulence in susceptible fish.     

Prevalence and effects of the cymothoid isopod (Ceratothoa oestroides,Risso 1816) on cultured meagre (Argyrosomus regius,Asso 1801) in the Eastern Adriatic Sea

Meagre (Argirosomus regius) is a relatively new farmed fish species in Croatian mariculture. This study is the first attempt to determine the prevalence of cymothoid isopod parasite Ceratothoa oestroides and its effects on cultured meagre in the Mediterranean area. When analysing growth of meagre at two sites in the central part of the Eastern Adriatic Sea, the greatest difference in total fish length was recorded in March 2016, when fish with parasites were 33% smaller than fish without parasites (24.47 ± 3.29 vs. 16.28 ± 1.01 cm; p < .001). The largest difference in mass was also recorded during sampling in March, when parasitized fish was 74% lighter than the unparasitized fish (171.75 ± 72.96 vs. 44.77 ± 6.57 g; p < .001). The presence of the cymothoid isopod in the buccal cavity was observed, and caused fish deformation throughout the entire duration of the study. Also, female parasites with pulli II in marsupium were found. Based on the determined prevalence and effects on production and health status, monitoring of the interaction between C. oestroides and meagre should be considered in future management plans for cultivation of this promising species for Mediterranean aquaculture.     

Seasonal dynamics and yearly change in the abundance of metacercariae of <Emphasis Type="Italic">Parabucephalopsis parasiluri</Emphasis> (Trematoda: Bucephalidae) in the second intermediate host in the Uji–Yodo River,central Japan

An introduced pathogenic fish trematode, Parabucephalopsis parasiluri Wang, 1985 (Digenea: Bucephalidae), was studied to determine the seasonal fluctuation in its metacercariae abundance. The timing of the recruitment period of the metacercariae and the relationship between yearly fluctuation in metacercarial abundance and some environmental factors were also examined to develop an effective plan for disease control. Monthly changes in metacercarial abundance in the caudal fin of pale chub (Zacco platypus) and of the prevalence of the first intermediate host (golden mussel Limnoperna fortunei) suggest that P. parasiluri generally has an annual life cycle. The metacercarial abundance in chub increased when the water temperature fell below 7°C in winter, but the rapidity of the increase varied between 2007 and 2008. The fluctuations in the abundance of metacercariae in winter from 2001 to 2008 showed that mean flow rate and mean water level in January were negatively related to the infection level each year, and positively related to the mean water temperature. Based on these results, we propose a control plan for parabucephalopsiosis involving discharge control; that is, more than 50 m³/s (corresponding to 150 m³/s in the Yodo River) of water should be flushed from upstream dams for a period of at least one week starting on the day when the water temperature falls below 7°C.     

An evaluation of replacing fish meal with cottonseed meal protein hydrolysate in diet for juvenile blunt snout bream (Megalobrama amblycephala): Growth,antioxidant, innate immunity and disease resistance

This study evaluated effects of fishmeal replacement by cottonseed meal protein hydrolysate (CPH) on growth, antioxidant and immunity of Megalobrama amblycephala and its resistance to Aeromonas hydrophila. Fish (average weight: 38.66 ± 0.08 g) were divided into five groups and fed with five isonitrogenous (320 g/kg crude protein), isolipidic (70 g/kg crude fat) and isocaloric (17.8 MJ/kg gross energy) diets replacing fishmeal with 0%, 1%, 3%, 5% and 7% CPH, respectively. The control diet contained 60 g/kg fishmeal. Final weight and weight gain of fish fed 5% and 7% CPH were significantly lower than that of fish fed control diet (p < 0.05). 3% CPH significantly increased total protein, globulin, acid phosphatase, C3 and C4 contents of plasma and total‐superoxide dismutase and catalase activities of liver (p < 0.05), as well as upregulated the antimicrobial peptides 1 and 2 (Leap‐1 and Leap‐2) expression levels in liver and spleen (p < 0.05). After challenge, the lowest mortality was observed in fish fed 3% CPH, and it was significantly lower than that in fish fed the 7% CPH (p < 0.05). In conclusion, dietary fishmeal replacement by 3% CPH could increase antioxidative capacity, as well as enhance immunity of fish.     

Assessing the feasibility of using pomegranate (Punica granatum) seed oil,rich in conjugated linolenic acid,as a lipid source in the diet of common carp,Cyprinus carpio,juveniles

In this study, the feasibility of using pomegranate seed oil, rich in conjugated linolenic acid and its partial replacement for fish oil in fish diet were investigated. Common carp, Cyprinus carpio, juveniles (1.8 ± 0.1 g) were fed four isonitrogenous and isolipidic diets with similar basal composition but different oil mixture containing 100% fish oil (A), 50% fish oil +50% sunflower oil (B), 50% fish oil +25% sunflower oil +25% pomegranate seed oil (C) and 50% fish oil +50% pomegranate seed oil (D) for 8 weeks. The highest weight gain was observed in fish fed diet D (p < 0.05). Test diets had no significant effect (p > 0.05) on saturated and monounsaturated fatty acid contents of fish muscle. Docosahexaenoic acid (22:6n‐3; DHA) was significantly lower in the muscle of fish fed diet B (p < 0.05) compared to those fed diet A. However, there was no significant difference in the muscle DHA content of fish fed diets A, C, or D. No specific hepatocyte damage associated to dietary pomegranate seed oil was found in this study. This study showed a 50‐50 combination of fish oil and pomegranate seed oil could be used as dietary lipid source for common carp without any adverse effect on growth performance or muscle n‐3 content while accumulated punicic acid in the muscle could be considered as added value for the final human consumer.     

Spatial avoidance of tu‐fish Schizopygopsis younghusbandi for different sounds may inform behavioural deterrence strategies

Water diversions for hydropower and other applications can potentially affect wild fish populations. Although some evidence indicates that acoustic barriers can prevent fish from entrainment into such infrastructures, few studies have been conducted on filtering candidate sound stimuli. Here, the effectiveness of three types of sounds acting as acoustic barriers to prohibit the movement of tu‐fish Schizopygopsis younghusbandi (Regan) was evaluated. The phonotaxic response of the fish to recordings of hissing sound (sound of Chinese alligator Alligator sinensis hissing), outboard motorboat and pile driving noise, compared to control conditions (recordings of ambient riverine noise), was investigated using playback approaches in a fibreglass tank. The tu‐fish reacted to the hissing sound at relatively low sound intensity by exhibiting negative phonotaxis with significantly more responses (F_3,79 = 49.590, p < 0.01) and faster swimming (F_3,219 = 310.086, p < 0.01) away from the sound source during the 10‐min trials than to control conditions. However, the fish were relatively impervious to the outboard motorboat and pile driving noise even when the sound intensities were increased. These results indicate that the potential use of the hissing sound to manipulate fish behaviour and to help protect them from water diversion structures.     

Weaning methods using formulated feeds for snakehead (Channa striata and Channa micropeltes) larvae

The culture of snakehead fish (Channa striata and Channa micropeltes) in Vietnam is limited, and snakehead culture has been banned in Cambodia, because traditional practices include capture of fingerlings from the wild as seed, as well as capture of small‐size (also known as trash fish or low‐value) fish. As hatchery breeding technology has improved, we investigated the optimal weaning practices for these two species. Both laboratory experiments and farm trials were conducted. For C. striata, the optimal weaning procedure is to begin at 17 days after hatch (dah) and wean the fish at 10% replacement of live feed with formulated feed per day. However, for C. micropeltes, the optimal procedure is to wait until 40 dah to begin weaning and then to wean the fish with a 10% replacement of live feed with formulated feed every 3 days. These results should enable farmers to domesticate snakehead culture in Vietnam and Cambodia and eliminate reliance on fish captured from the wild as both seed and feed.     

The trend of lessepsian fish populations with an emphasis on temperature variations in Iskenderun Bay,the Northeastern Mediterranean

The fish assemblages of the Eastern Mediterranean are highly variable owing to the Lessepsian migration. So far, there has been limited discussion about the temporal variation of Lessepsian populations, which may be a key to better understanding the establishment, persistence and spreading dynamics of these species. The objective of this study was, therefore, to develop an understanding of inter‐annual variations of Lessepsian fish populations through investigating the effects of climate conditions. For this purpose, we evaluated the data obtained from the seasonal bottom trawl surveys conducted over the course of 12 years, from 2004 to 2015, at the infra‐littoral zone of Iskenderun Bay. Our results indicated that Lessepsians constituted 27%, 62% and 85% of total teleost fishes in the number of species (LS‐%), biomass (LW‐%) and abundance (LN‐%), respectively. The linear trends showed that the dominance of Lessepsian fishes increased with annual rates of 1.9 (p < .01, LS‐%), 2.77 (p < .01, LW‐%) and 1.43% (p < .05, LN‐%) per year during the study period. In contrast, seasonal trend decomposition based on GAMMs revealed that the true shape of trends was non‐linear. The majority of the new Lessepsians entered the study area after 2009 when warmer conditions prevailed. Those new invaders such as Nemipterus randalli, Pomadasys stridens and Apogon smithi successfully settled in a short time and remarkably altered the composition of fish assemblages after 2010. We found that variations of lessepsian fish assemblages were correlated with the increase of annual minima and average values of sea surface temperature.     

Using stable isotope analysis to assess the relationship among dietary protein sources,growth, nutrient turnover and incorporation in Nile tilapia (Oreochromis niloticus)

Nile tilapia (1.20 g) were fed for 56 days in five treatments (FM100 containing only fish meal [FM] as a protein source; soybean meal (SBM) replace 25%, 50%, 75% and 100% of FM protein in the diets of FM75, FM50, FM25 and FM0, respectively) to assess the effects of dietary protein sources on growth, turnover half‐life of nitrogen and carbon stable isotopes (δ¹³C and δ¹⁵N) in muscle, isotope discrimination factors (Δ¹⁵N and Δ¹³C), and the relative contribution of protein sources to muscle growth. Results showed that the final body weight, weight gain and specific growth rate of fish fed diet FM25 were significantly higher than other treatments (p < .05). By day 35, fish under all treatments reached isotopic equilibrium, and the equilibrium values consistently increase as a function of stable isotope values in diets. Growth accounted for most isotopic changes in muscle and resulted in significantly shorter half‐lives of nitrogen and carbon in FM25 (p < .05). The Δ¹⁵N of FM25 and Δ¹³C of FM0 were significantly lower than other treatments (p < .05). The proportional contributions of SBM protein were significantly higher than their respective levels in FM75 and FM25 (p < .05), indicating a preferential incorporation of nitrogen from the SBM in muscle tissue.     

The extracts of Angelica sinensis restore the digestive and absorptive capacity through improving antioxidant status in digestive organs of fish treated with trichlorfon

Firstly, a linoleic acid emulsion and fish hepatopancreas homogenate were incubated with ethoxyquin and the extracts of Angelica sinensis. The results demonstrated that ethoxyquin showed the strongest protective effects against lipid oxidation of all of the examined compounds (p < 0.05). However, ethyl acetate extract of Angelica sinensis at high concentrations showed a stronger effect on lipid oxidation than that of ethoxyquin (p < 0.05). Next, seven experimental diets that contained 0.0, 1.0, 2.0, 3.0, 4.0, 5.0, and 6.0 g/kg of ethyl acetate extract of Angelica sinensis were fed to seven groups of carp (Cyprinus carpio var. Jian) respectively. After 60 days, carp were exposed to 2.4 mg trichlorfon/L in water for 4 days. The results displayed that trichlorfon exposure increased the contents of malonaldehyde and protein carbonyl in digestive organs and the activities of glutamate‐oxaloacetate and glutamate‐pyruvate transaminase in plasma, and decreased feed intake, the level of reduced glutathione, and the activities of trypsin, chymotrypsin, lipase, alpha‐amylase, Na⁺,K⁺‐ATPase, alkaline phosphatase, antisuperoxide anion, antihydroxyl radical, superoxide dismutase, glutathione reductase, and glutathione S‐transferase in digestive organs of carp (p < 0.05). Moreover, the dietary ethyl acetate extract of Angelica sinensis prevented the decrease in the above parameters in carp treated with trichlorfon (p < 0.05). These results revealed that the dietary ethyl acetate extract of Angelica sinensis could quench the trichlorfon‐induced structural and functional damage by improving the antioxidative capacity of the digestive organs of fish. Therefore, the extract of Angelica sinensis could be used as an inhibitor of trichlorfon stress in fish.     

Effect of natural pigment sources on colouration of red zebra cichlid (Maylandia estherae Konings, 1995)

This study was done to assess the effect of the colouration of the red zebra cichlid (Maylandia estherae), using beet root red (Beta vulgaris ruba) and henna (Lawsonia inermis). The fish with an average weight of 1.21 ± 0.69 g was placed in 12 aquariums. Fifteen fish were placed in each aquarium. The fish were fed with diets which were without carotenoid supplement (AK), containing astaxanthin (AA), beet root red (AP) and henna (AI). Except the AK, each group contained 50 mg/kg carotenoid additives. As a result of the experiment, total carotenoid values between groups were not significant (p > .05). The redness (a*) value of groups was significant (p < .05), and the values of brightness (L*) and yellowness (b*) were not significant (p > .05). Samples were kept in the freezer at ?20°C for 120 days to see whether the fish kept their colour. All groups decreased compared with the 50th day. This difference in groups except the AP was significant (p < .05). The FCR, SGR and weight gain% was not significant (p > .05). The survival was 97.28%, and it was the same in all groups. The study concluded that natural carotene sources with lower costs had similar effects with astaxanthin.     

The effects of temperature on respiration of Amur sturgeon,Acipenser schrenckii,at two acclimation temperatures

In order to clarify the respiratory responses strategy of Amur sturgeon Acipenser schrenckii exposed to water temperature changes, respiratory parameters of the fish were studied under two temperature regimes: fish acclimated at 13°C for Group I, temperature was increased to 16°C, 19°C, 22°C and 25°C and then returned stepwise to 22°C, 19°C, 16°C and 13°C; and fish acclimated at 25°C for Group II, the water temperature was reduced in steps to 22°C, 19°C, 16°C and 13°C, subsequently, returned to 16°C, 19°C, 22°C and 25°C. The results showed that the respiratory frequency (f_R), oxygen consumption rate (VO₂) and gill ventilation (V_G) of the fish were directly dependent on the acute temperature in both acclimation groups (p < .05). The initial 25°C VO₂ in Group II was significantly higher than the initial 13°C VO₂ in Group I (p < .05), but was significantly lower than that at 25°C in Group I (p < .05). In Group I, respiratory stroke volume (V_S.R) of fish significantly increased or decreased with the acute temperature increases or decreases, respectively (p < .05); oxygen consumption efficiencies (EO₂) of fish did not significantly show differences when temperature increased to 25°C from 13°C (p > .05), but the EO₂ significantly declined while returning to acclimation temperature (p < .05). In Group II, the V_S.R of the fish did not significantly change with acute temperature fluctuations between 25 and 13°C (p > .05), while the EO₂ increased with acute temperature increases (p < .05). The Q₁₀ values for f_R, VO₂, V_S.R, V_G and EO₂ were 1.53–1.72, 1.92–2.06, 1.07–1.60, 1.78–2.44 and 1.11–1.65 at 13–25°C of temperature interval respectively. Amur sturgeon showed partial metabolic compensation to temperature changes. The study results suggest that the ability of Amur sturgeon to regulate metabolism in response to acute temperature changes makes this species good adaptability in the aquaculture rearing.     

Effects of fish origin probiotics on growth performance,immune response and intestinal health of shrimp (Litopenaeus vannamei) fed diets with fish meal partially replaced by soybean meal

This study was conducted to evaluate the application of four fish origin probiotics to relieve the side effects induced by SBM in shrimp. Shrimps were fed with high fish meal diet (C0, positive control containing 500 g/kg FM and 0 g/kg SBM), low fish meal diet (C, control containing 250 g/kg FM and 340 g/kg SBM) or the control diet (C) supplemented, respectively, with 1.0 × 10⁸ CFU/g Bacillus pumilus SE5 (T1), Psychrobacter sp. SE6 (T2), Enterococcus faecium MM4 (T3) or Bacillus claussi DE5 (T4). After 6 weeks of feeding, the growth performance, hepatopancreatic digestive enzymes, intestinal histological structure and immune parameters were determined. The results showed that compared with high FM group (C0), significantly lower WGR and SGR as well as higher FCR were observed in the low FM group (C) (p < .05). Compared with the control, significantly lower FCR was observed in treatment T1 (p < .05), but not in treatments T2–T4. Protease, amylase and lipase activities in all the treatments (T1‐T4) were significantly higher than the control (p < .05). GOT and GPT activities in the control were significantly lower than the C0 (p < .05), while higher MDA level was recorded in the control (p < .05). Meanwhile, higher GPT activities were observed in treatments T1‐T4 compared with the control (p < .05). Compared with the C0, lower SOD, ACP and AKP activities were observed in the control. Significantly improved SOD and AKP activities were observed in all probiotic feeding groups compared with the control (p < .05). The control diet led to significant reduction of intestinal wall thickness and villus height compared with the C0 (p < .05), while significantly higher intestinal wall thickness and villus height were exhibited in all the probiotic groups compared with the control (p < .05), except intestinal wall thickness in treatment T3. Thus, these results demonstrated that the four fish origin probiotic strains could relieve the side effects induced by high level of SBM in shrimp, while probiotic B. pumilus SE5 showed the best performance.     

Effects of alternative dietary lipid sources on growth performance,health status and fillet fatty acid composition of hybrid sturgeon (Acipenser baeri Brandt ♀ × Acipenser schrenckii Brandt ♂)

An 8‐week trial was conducted to determine the effects of total replacement of 12.9% fish oil (FO) with soybean oil (SBO), peanut oil (PNO), sunflower seed oil (SFSO), corn oil (CO) and canola oil (CNO) on growth performance, health status and fillet fatty acid composition of hybrid sturgeon (194.28 ± 0.14 g). Compared to the FO group, dietary SBO decreased growth performance (p < .05), increased serum glucose and hepatic lipid content (p < .05). No obvious adverse effects on growth performance and health status were observed in PNO, SFSO and CO groups (p > 0.05). The fish fed with CNO had increased growth performance (p < .05), reduced serum ALT, AST, LDL‐C (p < .05) and enhanced serum GSH‐Px, T‐AOC, and LZM, MPO, C4 (p < .05). The contents of C18:1n9, C18:2n6, and ∑n‐3 PUFA and ∑n‐6 PUFA in fillets showed a positive linear correlation with the diets (p < .05). In summary, PNO, SFSO and CO are probable alternative lipid sources to fully replace FO. Hybrid sturgeon prefers to use CNO as a lipid source with improved growth performance and health status. The fillet fatty acid composition mirrors the dietary fatty acid composition.     

Dietary fish oil replacement by soybean oil: Effect on plasma vitellogenin,sex steroids and ovarian steroidogenesis in Chinese strip‐necked turtles (Mauremys sinensis)

In order to investigate the effects of dietary fish oil replacement, the turtles (Mauremys sinensis) were fed four experimental diets for 10 months: FO (100% fish oil), FSO (70% fish oil and 30% soybean oil), SFO (30% fish oil and 70% soybean oil) and SO (100% soybean oil), sampled at pre‐vitellogenesis, vitellogenesis and post‐vitellogenesis. The results showed that plasma gonadotropin‐releasing hormone (GnRH) levels were the highest at pre‐vitellogenesis, which promoted the secretion of gonadotropin and sex steroids. Therefore, plasma luteinizing hormone (LH) and estrogen (E₂) levels were significantly increased at post‐vitellogenesis (p < 0.05), while follicle‐stimulating hormone (FSH) levels increased at vitellogenesis (p < 0.05). The FO and FSO groups had significantly higher GnRH and E₂ levels than the other two groups (p < 0.05). In addition, plasma vitellogenin (Vtg) levels significantly increased at vitellogenesis and post‐vitellogenesis (p < 0.05), which were significantly higher in the groups of FO and FSO than SO (p < 0.05). Moreover, the expression levels of hepatic estrogen receptor α (Erα) mRNA were significantly increased at vitellogenesis and post‐vitellogenesis while ovarian Cyp19α1α mRNA were significantly increased at post‐vitellogenesis (p < 0.05), and both were the lowest in SO. Taken together, the replacement of fish oil with 66.7% soybean oil is feasible.     

Effect of temperature on growth performance of greater amberjack (SERIOLA DUMERILI Risso 1810) Juveniles

In order to successfully diversify Mediterranean aquaculture, it is necessary to determine optimum culture conditions of potential candidate species such as greater amberjack (Seriola dumerili). Among culture conditions, rearing temperature is a key factor for achieving optimum growth and maintaining fish welfare. However, little is known about the optimum culture conditions of greater amberjack (Seriola dumerili). Thus, the aim of this study was to determine the effect of three different rearing temperatures (17, 22 and 26°C) during 120 days on growth performance, body morphometry, biochemical composition, gut transit and liver morphology of greater amberjack (Seriola dumerili) juveniles. After 120 days of rearing, fish raised at 26°C showed higher (p < .05) body weight and specific growth rate than fish held at lower temperatures, as well as improved feed utilization, protein efficiency and nutrient retention percentages. Fish stomach emptying was faster (p < .05) in fish raised at 26°C than in fish held at 22°C and 17°C. Similar results were obtained for gut transit time, being gut emptying faster (p < .05) in fish reared at 26°C than in fish cultured at lower temperatures. Rearing temperature also induced changes in fish morphology which resulted in a higher (p < .05) caudal propulsion efficiency index for fish reared at 26°C. Based on these results, we conclude that greater amberjack fingerlings perform better at 26°C than at 22°C or 17°C.