Seasonal Changes in the Milt Quality of Waigieu Seaperch,Psammoperca waigiensis: Implications for Artificial Propagation

Milt quality of Waigieu seaperch was sampled at the beginning, the middle, and the end of the spawning season to assess if the sampling season has an effect on milt quality parameters. The milt volume and total sperm production were higher at the middle of the spawning season while the sperm concentration in milt was significantly higher at the beginning and the end of the spawning season. Sperm morphology and the major parameters of seminal plasma (pH, total protein, Mg²⁺, or Ca²⁺ concentrations) did not differ throughout the spawning season. The concentrations of Na⁺ and the osmolality increased throughout the spawning season. The percentage of motile cells did not differ during the spawning season while the duration of sperm motility (swimming duration) and velocity (swimming speed) were significantly different during the spawning season. The fertilization rate (75.7 ± 6.8%) and hatching rate (56.5 ± 3.1%) at the middle of the spawning season were higher than at the beginning and end periods. Results indicated that milt quality parameters and fertility success in the middle of the spawning season were higher compared to earlier and later sampling dates. Thus, we recommend collecting milt during this time for maximal fertilization and hatching success.     

Effects of dopamine 2 receptor antagonist on sex steroid levels, oocyte maturation and spawning performances in Waigieu seaperch (Psammoperca waigiensis)

The present study has investigated the effects of domperidone (DOM), a dopamine 2 receptor antagonist, on plasma steroid hormone levels and reproductive performances of a female tropical marine finfish, Waigieu seaperch (Psammoperca waigiensis), with potential for cultivation in Vietnam. We showed that oral treatment of DOM during early stage of the reproductive cycle had no significant effects on the maturation and reproductive performances of the female fish, while plasma steroid hormone (testosterone (T), 11-ketotestosterone (11-KT), 17β-estradiol (E2) and progesterone (P)) levels were modulated based on month, DOM dose and the individual hormones measured. Overall, these findings suggest that DOM may not be needed for the induction of maturation and spawning of this species under aquaculture conditions. The data in the present study are significant in highlighting practical efforts for reducing drug use, production costs and for a sustainable aquaculture in a developing country such as Vietnam.     

Reproductive cycle of the rock oyster,Striostrea prismatica (Gray, 1825) from two locations on the southern coast of Ecuador

The reproductive cycle of the rock oyster Striostrea prismatica was determined at two fishing areas, General Villamil and Ayangue (located on the southern coast of Ecuador), between May 2012 and April 2013. Monthly sampling campaigns were performed at both locations. The tissues were histologically examined to determine gonadal index (GI), oocyte development, follicular area coverage and sex ratio. Surface seawater temperature, salinity and chlorophyll a concentration were measured during samplings. Our results show a similar annual reproductive pattern at both locations. The GI reached maximum values during the summer. Oysters reached highest ripeness in January and February, while spawning occurred in February–March. Gametogenesis was linked to a consistently increasing follicular area (from 1.3 ± 0.7% to 85.8 ± 7.8%) and associated to surface seawater temperature. Spawning coincided with warm water temperature fluctuations and a seawater salinity decrease. No correlation was found with Chlorophyll a concentration. The sex ratio of sampled populations was 1:1, suggesting that oysters sizing more than 10 cm in shell length present a stable sex proportion in the population. The diameter of mature oocytes was significantly reduced (32.7%) during histologically preparations in comparison to fresh oocytes. Our study provides useful information of environmental factors that may control the observed gametogenesis and spawning activity of S. prismatica.     

Effects of supplementary fennel (Foeniculum vulgare) essential oil in diet on growth and reproductive performance of the ornamental fish,Convict cichlid (Cichlasoma nigrofasciatum)

This study evaluated the effects of diet containing 0 (C: control), 75 (D₁), 100 (D₂), 125 (D₃) and 150 (D₄) mg kg^?1 F. vulgare essential oil on growth and reproductive performance of C. nigrofasciatum. A total of 225 Convict cichlids female with mean weight (1.65 ± 0.02 g) were distributed into 15 glass aquaria (15 fish tank^?1) in triplicate treatments. During 40 days of experimental period, fish fed at 3% of their body weight daily. At the end of experiment, growth indices, gonadosomatic index and reproductive indices were determined. The best feed conversion ratio was obtained in D₄ (1.19 ± 0.03, P < 0.05). The addition of F. vulgare essential oil did not have any statistical effects on other growth indices (specific growth rate, weight gain and condition factor). Total survival rates in all treatments and control were uniformly high, ranging from 93% to 97% (P > 0.05). F. vulgare essential oil has no negative effect on survival rate of C. nigrofasciatum. There were no significant differences among protein content of fish body (P > 0.05). The lowest value of fat content (26.5 ± 0.5%) was observed in D_2, and it had significant difference with control and other groups (P < 0.05). The ash percentage in treatments fed with F. vulgare essential oil were higher than control fish (P < 0.05). The highest moisture content was detected in D₄ (72.68 ± 0.19%) and D₂ (71.23 ± 2%) groups. Among the used dosage, D₄ was the most effective dosage that could significantly increase GSI (11.06 ± 1.55%), fecundity (340 ± 21) and hatching ratio (92.33 ± 1.63%). There were no significant differences in diameter of eggs among various treatments (P > 0.05).     

Stimulatory effect of thyroid hormones improves larval development and reproductive performance in alligator gar (Atractosteus spatula) and spotted gar (Lepisosteus oculatus)

Development of alligator gar (Atractosteus spatula) and spotted gar (Lepisosteus oculatus) larvae was evaluated after exposure of embryos to thyroid hormones (TH) by two different methods of administration. For the first method, alligator gar embryos were placed in a water bath with triiodothyronine (T₃; 1 ppm for 2 h), and control treatment embryos were placed in a water bath without T₃. For the second method, spotted gar adult males and females were injected with different TH during induced spawning: a group was injected with T₃ [20 mg kg^?1 body weight (BW)], a second group with thyroxine (T₄; 20 mg kg^?1 BW), a third group with thyroid‐stimulating hormone (TSH; 4 IU kg^?1BW) and a control group with dimethyl sulfoxide. Both methods resulted in increases in the concentrations of T₃ and T₄ in embryos of both species. An increase in the alkaline enzymatic activity of TH‐treated larvae was observed as well as an increase in the RNA:DNA, RNA:Dry weight and DNA:Dry weight ratios at hatching. Some positive effects of TH application were: a significant increase in the hatching rate of spotted gar larvae from TH‐injected parents and a higher percentage of successful spawns. Evenness of larval sizes and a higher survival rate were observed in alligator gar larvae. Snout development was accelerated by TH treatment in both species.     

Exophiala angulospora infection in hatchery‐reared lumpfish (Cyclopterus lumpus) broodstock

Samples from moribund lumpfish were collected in a marine hatchery in Scotland in 2015. Black nodules were noted on the skin, and gills and fungal hyphae were extensively distributed in musculature and internal organs. Multifocal chronic inflammatory lesions displaced structures in all affected organs. Mortalities commenced on completion of spawning in May and were evenly distributed over the second year in the temperature range 11–15°C. The main systemic infection causing agent was initially identified based on morphological characteristics as an Exophiala species. Ribosomal DNA (rDNA) ITS regions of the isolates were subsequently sequenced confirming the isolates belonged to Exophiala genus. All isolates fell in a single phylogenetic cluster, which is represented by Exophiala angulospora. Fish were treated with either formalin or Bronopol or a combination of both, but there was no effect on the pattern or numbers of mortalities. Isolates were also tested against three different concentrations of Latrunculin A, Amphotericin B and Itraconazole with no success. It is of utmost importance to increase the knowledge on pathogen–host interactions to successfully develop sustainable control methods.     

Seasonal movements of Atlantic rock crab (Cancer irroratus Say) transplanted into a mussel aquaculture site

Approximately 73 000 Atlantic rock crab (Cancer irroratus) were captured in coastal waters and transferred to an estuarine mussel aquaculture site in Prince Edward Island, Canada, in an effort to control overgrowth by the invasive tunicate Ciona intestinalis. To assess whether transplanted crabs remained in the vicinity of mussel farms, acoustic tags were attached to 25 resident and 25 transplanted individuals (all males) and their movements were monitored for 1 year, from September 2006 to August 2007. Resident crabs tended to occupy (within 1.6 km) the middle estuary where the majority of mussel farms are located. They left this area during winter, possibly to reach upstream overwintering grounds, and most returned to the middle estuary in spring. In contrast, translocated crabs exhibited a marked downstream movement (<5.5 km distant) in autumn and winter and few returned into the middle estuary in spring. Results suggest that transplanting large numbers of additional rock crabs is not an effective means to reduce the effects of invasive tunicates on mussel farms.     

Early ontogeny of yellowtail tetra fish Astyanax lacustris (Characiformes: Characidae)

The ontogeny of the tetra fish Astyanax lacustris, from embryogenesis through the larval and juvenile periods, is presented. The eggs and larvae were obtained through induced reproduction. The larvae were collected at hatching and daily, until all stages of development were obtained and, later, once a week, until the juvenile period. The eggs are small, slightly adhesive and demersal, and have a transparent chorion, yellowish calf and meroblastic cleavage. The larvae hatch 19 hr after fertilization (26ºC). The standard length during initial development ranges from 2.17 to 18.10 mm. The larvae have a subterminal mouth, simple nostrils, a pair of adhesive organs on the back of the head (newborn larvae), spherical eyes and medium‐length intestines. The initial pigmentation is scarce, concentrated in the anteroposterior ends of the yolk sac, but intensifies from the flexion stage, with chromatophores in the mouth and in the cephalic region; the humeral region and the caudal peduncle have a macula at the end of the larval development. The total number of myomeres: 32–38, 15–20 preanal and 14–20 postanal. Juveniles showed similar morphology and pigmentation to adults. The number of fin rays: pectoral 11–12; pelvic 6–7; dorsal 10–11; and anal 27–29.     

Replacement of fish oil with a DHA‐rich Schizochytrium meal on growth performance,activities of digestive enzyme and fatty acid profile of Pacific white shrimp (Litopenaeus vannamei) larvae

This trial was conducted to evaluate the effects of replacing dietary fish oil with Schizochytrium meal for Pacific white shrimp (Litopenaeus vannamei) larvae (initial body weight 4.21 ± 0.10 mg). Six test microdiets were formulated using Schizochytrium meal to replace 0 g/kg, 250 g/kg, 500 g/kg, 750 g/kg, 1000 g/kg or 1500 g/kg fish oil DHA. No significant differences were observed in survival, growth, final body length and activities of digestive enzyme among shrimp fed different diets (p > .05). No significant differences were observed in C20:5n‐3 (EPA) in muscle samples (p > .05). C18:3n‐3 and C20:4n‐6 in muscle increased as Schizochytrium meal replacement level increased (p < .05). No significant differences were observed in C22:6n‐3 (DHA) and n‐3 fatty acids among shrimp fed diets that algae meal replaced 0 g/kg ‐ 1000 g/kg of fish oil. Shrimp fed diet R150 had higher DHA content than other groups and had higher n‐3 fatty acids than that of shrimp fed diets R50, R75 and R100 (p < .05). C18:2n‐6, PUFA and n‐6 fatty acids in muscle increased, while n‐3/n‐6 ratio decreased with increasing algae meal replacement level from 0 g/kg to 1000 g/kg (p < .05). In conclusion, Schizochytrium meal could replace 1500 g/kg fish oil DHA in the microdiets without negatively affecting shrimp larvae survival, growth and activities of digestive enzyme.     

Apoptosis inhibition of Atlantic salmon (Salmo salar) peritoneal macrophages by Piscirickettsia salmonis

To improve the understanding of the piscirickettsiosis pathogenesis, the in vivo apoptosis modulation of peritoneal macrophages and lymphocytes was studied in juvenile Salmo salar intraperitoneally injected with Piscirickettsia salmonis. Five fish were sampled at post‐exposure days 1, 5, 8 (preclinical), 20 (clinical) and 40 (post‐clinical period of the disease), and the leucocytes of their coelomic washings were analysed by flow cytometry (using the JC‐1 cationic dye), TUNEL and cytology to detect apoptotic cells. A selective and temporal pattern of apoptosis modulation by P. salmonis infection was observed. Apoptosis in lymphocytes was not affected, whereas it was inhibited in macrophages but only during the preclinical stage of the induced piscirickettsiosis. Hence, it is postulated that P. salmonis inhibits macrophage apoptosis at the beginning of the disease development to survive, multiply and probably be transported inside these phagocytes; once this process is complete, macrophage apoptosis is no longer inhibited, thus facilitating the exit of the bacteria from the infected cells for continuing their life cycle.     

Effects of putative dietary probiotics from the gut of milkfish (Chanos chanos) on the growth performance and intestinal enzymatic activities of juvenile Nile tilapia (Oreochromis niloticus)

Enzymes synthesized by the gut microbiome are recognized as vital for assisting host metabolism. This study was conducted to screen and identify bacterial isolates with enzyme-producing abilities from the intestine of milkfish Chanos chanos. Overall, 114 isolates were collected, of which 58% showed clear zones indicating various enzyme activities via plate-based assays. Specifically, 65 isolates were amylolytic, 1 isolate was cellulolytic, and 18 isolates exhibited both activities. The two most promising isolates—CC8 and CC27—were further subjected to spectrophotometric enzyme assays to determine their amylase, cellulase and protease activities. Results showed that amylase, cellulase and protease activities (6.00 ± 0.01, 0.52 ± 0.02 and 18.62 ± 0.16 U mg^?1 protein, respectively) were higher in CC8 than in CC27. Using 16S rRNA gene sequencing, the isolates were putatively identified as Vibrio sp. and Bacillus cereus respectively. At a suspension (mL) to feed (g) ratio of 3:25, dietary supplementation of putative probiotics was carried out to evaluate the growth performance, survival and enzymatic activities of juvenile Nile tilapia Oreochromis niloticus. Results revealed that probiotic-supplemented fish exhibited better growth performance—final average body weight, weight gain, specific growth rate and feed conversion ratio—along with increased intestinal enzymatic activities compared with the control (p < 0.05). Survival rates ranged from 80% to 90% and were statistically similar in all treatments (p > 0.05). This study concludes that the application of Vibrio sp. CC8 and Bacillus cereus CC27, supplemented either in monostrain or multistrain preparation, can promote growth and enzymatic activities in juvenile Nile tilapia.     

Acute responses of juvenile cobia Rachycentron canadum (Linnaeus 1766) to acid stress

Fish are potentially submitted to water acidification when reared in recirculating aquaculture systems. This study evaluated the responses of juvenile cobia Rachycentron canadum after acute exposure to acid water. Juvenile cobia (12.6 ± 0.5 g; 14.2 ± 0.2 cm) were acutely exposed to four pH levels (7.9 (control), 6.5, 6.0, and 5.5). After 24 h of exposure to different pH values, fish were sampled for physiological and histopathological evaluation. Acid water affected physiological parameters and induced morphological histopathologies on gill and skin of juvenile cobia, and these effects were more conspicuous with decreasing pH values. Acid stress induced blood acidosis in juvenile cobia, coupled to a decrease in bicarbonate (HCO₃^?) and saturated O₂ (sO₂) in fish blood. On the other hand, haematocrit, haemoglobin and glucose concentration increased their values (P < 0.01) comparing to control level. Hyperplasia with completely fusion of secondary lamella was observed in all pH treatments (6.5. 6.0 and 5.5), while telangiectasia and proliferation of chloride cells were present for fish exposed to pH 6.0 and 5.5. In skin hyperplasia and hypertrophy of mucous cells, necrosis of these cells for fish exposed to pH 6.0 and 5.5 was observed. The results of this study demonstrate that acute acid water exposition affected physiology and histopathology in juvenile cobia, especially at pH values below 6.5. Accordingly, particular attention must be given to pH during cobia reared in recirculating aquaculture.     

Menthol as anaesthetic for lambari Astyanax altiparanae (Garutti & Britski 2000): attenuation of stress responses

The anaesthetic potential of menthol was evaluated in lambari Astyanax altiparanae by exposing fingerlings to concentrations 50, 100, 150, 200, 250 and 300 mg L^?1 and measuring the induction and recovery times to deep anaesthesia, the mortality rates during and 96 h after procedure and after 6 min of continuous exposure. The effect of menthol on stress responses were evaluated by comparing glucose and cortisol levels of juveniles subjected to anaesthesia (50 mg L^?1), stress (air exposure) or pre‐anaesthesia associated to stress. All concentrations induced deep anaesthesia within 0.5 to 1 min, with recovery between 1.83 and 4.16 min, without mortality during the induction or up to 96 h after exposure. Induction time decreased and recovery time increased linearly as the menthol concentration increased. Continuous exposure to 50, 100 and 150 mg L^?1 concentrations resulted in mortality rates of 0%, 20% and 80% respectively. Anaesthesia or air exposure increase blood glucose but prior anaesthesia with menthol suppressed the elevation of cortisol caused by stress. Menthol has an anaesthetic effect and attenuates the stress response in lambari and 50 mg L^?1 is the most effective concentration for inducing deep anaesthesia in 1.0 min, safe for up to 6 min exposure.     

Effect of different culture conditions on the structural diversity of prokaryote communities in the sediment of earth ponds stocked with gilthead seabream Sparus aurata (Linnaeus, 1758)

In this study, we evaluate the use of polymerase chain reaction‐denaturing gradient gel electrophoresis (PCR‐DGGE) for monitoring the effect of different aquaculture practices on sediment prokaryote (Archaea and Bacteria) communities. The effect of initial fish (gilthead seabream Sparus aurata) stocking density on the structural diversity of prokaryote communities of earth ponds bottom sediments was evaluated using PCR‐DGGE after a 5 month grow‐out period. An identical approach was used to monitor the effect of supplying different fish feeds [commercial feed (CD) versus an ecofeed (ECO)]. One additional variable was the use of copper sulphate (CuSO₄) as an algicide in some of the experimental rearing tanks. The statistical analyses of prokaryote community profiles showed that the presence of fish in earth ponds significantly influenced the structure of sediment prokaryote communities, when compared with earth ponds without fish, independently of the stocking density. Our results also indicated that the structure of the prokaryote communities of earth ponds supplied with the ECO feed shared a strong similarity with that fed CD. Curiously, the use of CuSO₄ in ponds receiving the ECO feed promoted significant differences on the structural composition of the bacterial community, but not on the archaeal community. DGGE molecular fingerprints are suitable for fast evaluation of new management practices in food‐fish production on earth ponds by monitoring shifts on microbial communities in bottom sediments.     

Utilization of Caridina nilotica (Roux) meal as a protein ingredient in feeds for Nile tilapia (Oreochromis niloticus)

The effects of replacing fish meal with Caridina nilotica as a protein ingredient on growth performance, nutrient utilization, carcass, proximate composition and economic benefits in Nile tilapia (Oreochromis niloticus) culture was evaluated. Replacement of the FM with C. nilotica was done at 25%, 50%, 75% and 100% (D25, D50, D75 and D100) and the substitution effects was compared with the control diet (D0, 0% C. nilotica). After 140 days of culture, the best growth performance, nutrient utilization and economic benefits occurred in fish groups fed diets with 25% C. nilotica inclusion. However, growth performance in fish fed diets D50 and D75 were comparable with the control (P > 0.05). At 100% substitution level of FM with C. nilotica, the growth performance and fish survival was lower than control. Protein and lipid contents in the fish and their digestibilities were highest in diet D25 and decreased with increasing levels of substitution of FM with C. nilotica. This study demonstrate that utilization of local protein sources (C. nilotica) can be effectively used to replace up to 75% of FM in the diets without compromising growth performance, survival, nutrient utilization and economic benefits in O. niloticus culture.     

Evaluation of nutritional values of selected commercial fish meal sources in turbot (Psetta maxima) diets

This study was conducted to evaluate nutritional values of selected commercial fish meals (FM) with two experiments in diets of turbot. In experiment I, five diets based on two Peruvian anchovy meals (one is a flame‐dried FM: Peru‐1 and the other steam‐dried FM: Peru‐2), a Danish FM (Danish LT), a domestic anchovy LT meal (Domestic LT) and an Alaskan white FM (WFM) as major protein source were formulated to contain 56% protein. The diets were fed to fish with an initial average weight of 119.4 ± 0.1 g for 9 weeks. Growth rate, feed utilization, whole body and visceral compositions, nitrogen, lipid and energy balances did not significantly change in Experiment 1 among the treatments. In Experiment 2, four diets based on three FMs (Domestic LT, Danish LT and Peru‐1) and their mixture (Mix FM) were formulated to contain 50% protein and fed to triplicated groups of fish with an average initial weight of 51.4 ± 0.1 g for 6 weeks. Once again, there were no significant differences in growth rate and feed consumption among the treatments. However, fish on Mix FM diet had significantly better FCR and PER than the others. The results of two experiment indicated that Danish LT and Domestic LT were better in terms of phosphorus (P) retention and losses than two Peruvian FMs and WFM, suggesting that although different sources of FMs were comparable in terms of growth and feed utilization, they could lead to substantial differences in environmental impacts.     

Susceptibility of Caligus rogercresseyi collected from the native fish species Eleginops maclovinus (Cuvier) to antiparasitics applied by immersion

A major challenge for Chilean salmon farming is infestation by the ectoparasite Caligus rogercresseyi. In addition, there is evidence that a loss of chemotherapeutic treatment efficacy against important fish pathogens is occurring in salmon farming, including antiparasitic efficacy. Currently, there are known techniques that allow the determination of the susceptibility profile of parasites to antiparasitic treatment. However, there is scarce information about both threshold values and categorization of antiparasitic susceptibility for C. rogercresseyi. Bioassay technique allowed the determination of both mean values and the natural variation of EC50%, which were contrasted with available susceptibility thresholds. Results allowed to determine that parasites from the native fish host, Eleginops maclovinus, are susceptible to azamethiphos, deltamethrin and cypermethrin treatments, showing a high susceptibility profile to antiparasitics.     

Dietary supplementation of Tribulus terrestris extract improves growth and reproductive performances of the male Nile tilapia (Oreochromis niloticus)

Effects of dietary supplementation of Tribulus terrestris (TT) and 17α‐methyl testosterone (MT) on growth performance and reproductive efficiency of male Nile tilapia, Oreochromis niloticus (N = 75, initial weight 60 ± 3.251 g), were evaluated. Five experimental treatments in triplicate were fed on basal diet (30% crude protein) (control group, CG), basal diet containing 60 mg MT (MT group) and basal diet containing 250, 500 and 750 mg/kg diet TT (TT250, TT500 and TT750 groups), respectively, for consecutive 45 days. Results revealed that the fish received TT in diet showed better growth performance (final body weight, weight gain, feed conversion ratio, specific growth rate, testes weight and gonadosomatic index) compared with MT and CG (p < .05), as well as for haemoglobin content and red blood cell count (p < .05). The highest level of testosterone, 11‐keto testosterone, sperm concentration and vitality was recorded in TT750 followed by TT500, TT250 and MT groups, while the lowest value was recorded in the CG (p < .05). The highest seminiferous tubule diameter was recorded in TT750 followed by TT500, TT250 and CG, while the lowest diameter was recorded in the MT group (p < .05). Fish received TT showed normal dilated seminiferous tubule filled with large amount of free sperms within their lumen in a dose related effect. In conclusion, male Nile tilapia dietary supplementation with different inclusions of Tribulus terrestris extract specially 500 and 750 mg/kg diet improves growth performance, health condition, semen quality and reproductive efficiency without any harmful effect on water quality.     

The annual reproductive cycle and sex inversion of the Picnic seabream,Acanthopagrus berda (Forsskål 1775) from Indian waters: Histological and morphometric description

The annual reproductive cycle of picnic seabream, Acanthopagrus berda (Forsskål, 1775), one of the potential aquaculture candidate from estuarine waters of Calicut, Kerala (India) was studied. Based on the morphological and histological studies, the ovotestes of A. berda were classified as active male, active female, inactive male, inactive female, transitional and undifferentiated. Histological observation of transitional gonads showed signs of degeneration in the testicular lobe, proliferation of connective tissue and empty sperm ducts indicating protandrous hermaphroditism in A. berda. Ovary was classified into seven maturity stages (virgin, developing virgin, developing, maturing, mature, running, spent) and testis into five maturity stages (resting, maturing, mature, running, spent). Gonadal development in A. berda indicated resting phase (February–July), pre‐spawning phase (March–August) and spawning phase (August–December). Inactive (24.6%) and active males (21.6%) were observed as dominant in smaller length classes (140–250 mm TL), whereas inactive (18%) and active females (51%) were observed as dominant in larger length classes (251–450 mm TL). Few primary females (28.1%) were observed in smaller (below 250 mm TL) and few primary males (28.5%) were observed in larger length classes (above 250 mm TL). From the present study, it can be concluded that in A. berda, most of the individuals function first as males and then change sex to female, but few continue to function as either male or female throughout their lifespan indicating digynous protandrous hermaphroditism.