Effect of different permeable and non-permeable cryoprotectants on the hatching rate of rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>) embryos

The purpose of the present study was to investigate the toxicity of cryoprotectants on the hatching rate of rainbow trout (Oncorhynchus mykiss) embryos. Epiboly and first eye pigmentation stage embryos were immersed in six permeable cryoprotectants, dimethyl sulfoxide (DMSO), glycerol (Gly), methanol (MeOH), propylene glycol (PG), ethylene glycol (EG), and acetamide (Ac), in concentrations of 1–5 M for 5 or 10 min and two non-permeable cryoprotectants, sucrose (Suc) (10%, 15%, 20%) and polyvinyl pyrrolidone (PVP) (5%, 10%, 15%) for 5 min. The embryos were then washed and incubated until hatching occurred. The toxicity of the cryoprotectant was assessed by the hatching rate. The results illustrated that permeable cryoprotectant toxicity for rainbow trout embryos increased in the order of PG < DMSO < MeOH < Gly < EG < Ac. The hatching rate of the embryos treated with permeable cryoprotectants decreased (P < 0.05) with increased concentration and duration of exposure. There were no significant decreases in hatching rate of embryos treated with sucrose and PVP with the increase of concentration; sucrose had higher hatching rates than PVP. Rainbow trout embryos at first eye pigmentation stage exhibited greater tolerance to cryoprotectants than embryos at epiboly stage.     

Growth, reproductive performance, muscle and egg composition in grass carp, Ctenopharyngodon idella (Valenciennes), fed hydrilla or formulated diets with varying protein levels

Growth, reproductive performance, muscle and egg composition were investigated in grass carp, Ctenopharyngodon idella (Valenciennnes), fed hydrilla or formulated diets with varying protein levels. Five experimental diets, with varying levels (20%, 25%, 30%, 35% and 40%) of crude protein (CP), were used. One of the fish groups was fed hydrilla. Fish (44.1±0.3 cm; 913±9 g) were stocked (20 tank^?1) in outdoor concrete tanks (20 × 10 × 1.5 m) in duplicate, and fed to satiation, twice daily, at 09:00 and 17:00 hours for the experimental duration of 360 days. High (P<0.05) weight gain was recorded in fish fed 30% and 35% CP diets. However, values for gonadosomatic index (GSI), egg diameter, relative fecundity (eggs kg^?1 body weight), fertilizability and hatchability (%) were comparable (P>0.05) in fish at ≥25% of dietary protein intake. Hydrilla‐fed fish exhibited lower (P<0.05) values for the measured parameters. Crude protein content in muscle increased with dietary protein level. Highest (P<0.05) muscle protein was obtained in fish fed 35% CP diet. Muscle fat was comparable (P>0.05) among fish receiving formulated diets. Ash content was not significantly (P>0.05) different among fish of different dietary groups. Moisture content in fish fed formulated diets, with the exception of 20% CP diet, did not vary significantly (P>0.05). Eggs of fish fed formulated diets contained higher CP and fat contents than those of hydrilla‐fed fish. High (P<0.05) moisture content was noted in the eggs of hydrilla‐fed fish. Ctenopharyngodon idella fed formulated diet, with a minimum of 25% CP, showed better reproductive performance than those fed hydrilla.     

Morphological diversity of Paramoeba perurans trophozoites and their interaction with Atlantic salmon,Salmo salar L., gills

Amoebic gill disease (AGD) caused by the ectoparasite Paramoeba perurans affects several cultured marine fish species worldwide. In this study, the morphology and ultrastructure of P. perurans in vitro and in vivo was investigated using scanning and transmission electron microscopy (SEM and TEM, respectively). Amoebae cultures contained several different morphologies ranging from a distinct rounded cell structure and polymorphic cells with pseudopodia of different lengths and shapes. SEM studies of the gills of AGD‐affected Atlantic salmon, Salmo salar L., revealed the presence of enlarged swellings in affected gill filaments and fusion of adjacent lamellae. Spherical amoebae appeared to embed within the epithelium, and subsequently leave hemispherical indentations with visible fenestrations in the basolateral surface following their departure. These fenestrated structures corresponded to the presence of pseudopodia which could be seen by TEM to penetrate into the epithelium. The membrane–membrane interface contained an amorphous and slightly fibrous matrix. This suggests the existence of cellular glycocalyces and a role for extracellular products in mediating pathological changes in amoebic gill disease.     

Effects of Bacillus subtilis on the water quality,stress tolerance,digestive enzymes,growth performance,immune gene expression,and disease resistance of white shrimp (Litopenaeus vannamei) during the early hatchery period

Aquaculture International - In the present study, the white shrimp, Litopenaeus vannamei, was supplemented with the probiotic Bacillus subtilis IS02 in order to improve the larval survival rate....     

Understanding the economic and farming practices driving species selection in aquaculture within the Mymensingh division of Bangladesh

Aquaculture is a major supplier of animal protein for Bangladesh’s population, and the Mymensingh division is a major contributor to finfish aquaculture, producing 43% of the total pond pangasius and 9% of the total amount of tilapia (figures from 2018). We conducted a finfish farmer survey covering Netrokona, Jamalpur and Mymensingh districts to understand current finfish farming practices and identify factors that drive farmers in their species choice between pangasius or tilapia cultivation. We found that most finfish farmers in Mymensingh are experienced practitioners and practise polyculture with a range of stocking densities for each species. Using an economic model of polyculture practice, we have shown that over a production cycle, pangasius gain body mass at a rate nearly 4 times greater than that for tilapia, resulting in substantially larger revenues and providing a strong incentive for their culture. High levels of tilapia aquaculture likely persist due to their short production cycle and an associated decreased economic risk due to crop loss from disease, both factors providing a strong incentive for their culture. Our findings also indicate production yield differences through different species selection in polyculture systems. For example, co-culturing pangasius, tilapia and carp together was less productive than co-culture of pangasius with tilapia. Furthermore, higher yields of tilapia were obtained when co-cultured with carp compared with pangasius, the reasons for which are not known and warrant further investigation. Our study uses information provided by finfish farmers to produce a useful guide on fish species choices to maximise production yields, and therefore food production, from their ponds.

     

Karyological analysis of endangered Caspian salmon, Salmo trutta caspius (Kessler, 1877)

The karyotype and chromosomal characteristics of endangered Caspian salmon, Salmo trutta caspius, in the southern part of the Caspian Sea were investigated. From the total of 60 mitotic metaphases achieved from 15 individuals, 15, 9 and 36 metaphases were with the mode <76, 76 and 80 representing 25%, 15% and 60% of metaphases respectively. So, the most common pattern of chromosome number was 80 (36 metaphases, 60%) and the number of diploid chromosomes was thus confirmed as (2n=80) of this subspecies. The karyotype consists of seven metacentric, five submetacentric and 28 telocentric pairs. The karyological parameters of the Caspian salmon, the centromic index, arm ratio, relative length and length variation range of chromosomes, were 0–0.5, 1–∞, 0.011–0.045 and 0.507–2.028 μm respectively. The total length of chromosomes in haploid series was 44.776 μm and fundamental number of chromosome arms was 104. This study may provide the first knowledge on chromosome analysis in Caspian salmon and add basic information useful for its chromosomal manipulations.     

The role of dietary L‐ascorbyl‐2‐polyphosphate on the growth and physiological functions of beluga,Huso huso (Linnaeus, 1758)

Effects of dietary ascorbic acid (AA) supplementation were carried out on growth performance and physiological indices in juvenile beluga Huso huso fed different levels of dietary L‐ascorbyl‐2‐polyphosphate as AA source consisting of 0 (control), 100, 200, 400, 800 and 1600 mg AA kg^?1 diet for 16 weeks. No significant differences were found in growth performances between treated groups except for condition factor. Using AA caused significant differences in haemoglobin, number of red blood cells, white blood cells, aspartate aminotranspherase and lactate dehydrogenase, while no significant difference was found in haematocrit, mean corpuscular haemoglobin concentration, differential white blood cells count and alkaline phosphatase activity at the end of the experiment. Lysozyme activity after 8 weeks was significantly affected by dietary treatments with the lowest value in fish fed control diet, but not at completion of 16‐week feeding trial. Liver AA concentration showed a significant increase in correlation with dietary AA increase. Air exposure stress test showed significant differences among the treatments in case of cortisol and glucose concentrations. Also between pre‐ and post stress, significant changes were observed in some of treatments. The lowest and highest levels of cortisol were 9.2 ± 3 (in 200 mg kg^?1) and 16.8 ± 5.1 ng mL^?1 (in control), 6 h post stress (P < 0.05) respectively. Also, the lowest and highest levels of glucose were measured in fish fed 200 and 800 mg AA kg^?1 respectively. The obtained results showed that most growth parameters were not affected by dietary AA, but some physiological and immunological parameters of this species were influenced by this vitamin. We suggest that under rearing conditions, AA should be added to the diet especially during early life stages for improving health status and resistance to stressors.     

Effects of the prebiotic mannan‐oligosaccharide on feed deprived zebrafish: Growth and reproduction

This study was designed to investigate whether the prebiotic mannan‐oligosaccharides (MOS) can reduce the deleterious impacts of feed deprivation on growth and reproduction in zebrafish. In the growth performance experiment, juvenile fish were distributed in the following four treatments: normal‐control (NC), starved‐control (SC), normal‐prebiotic (NP) and starved‐prebiotic (SP). After 8 weeks, NP and SC fish showed the highest and lowest growth patterns, respectively among treatments. Standard length, specific growth rate and feed conversion ratio did not differ significantly between NC and SP treatments. Autochthonous lactic acid bacteria (LAB) were significantly higher in NP and SP than the NC and SP treatments. Feed restriction resulted in significantly lower concentrations of thyroxine. In the reproductive performance experiment, additional juveniles were fed as in the growth experiment. Crossing in the final week of the experiment resulted in successful spawning in only NP fish, which showed mature sperm and oocytes in histological examinations. The number of spermatozoa was significantly lower in the fish that experienced feed restriction; however, the oocytes of SP females were at the same maturation level to that observed in NC females. Sex‐steroids changed after both starvation and MOS supplementation where NC and SP showed no differences in the levels of testosterone and female's 17β‐estradiol. These results indicate that MOS supplemented diet reduced some side effects of feed deprivation (final weight and length, SGR, FCR and levels of LAB and T3), and suggest that supplementation of the diet with MOS may ameliorate some of the negative effects of feed deprivation in zebrafish.     

Economic feasibility of goldfish (Carassius auratus Linn.) recirculating aquaculture system

Economic analysis of a goldfish (Carassius auratus Linn.) recirculating aquaculture system (RAS) with rearing tank capacity of 5 m³ (RT5) has been evaluated based on two culture period in 2009 and 2010. The stocking density of goldfish was kept at 100 numbers per m³ of rearing water volume. Furthermore, based on the data obtained from RT5, four more hypothetical RASs of rearing tank capacities of 10 m³ (RT10), 20 m³ (RT20), 50 m³ (RT50) and 100 m³ (RT100) were conceptualized for economic analysis that assess and compare the effects of economies of scale on profitability. The payback period, accounting rate of return (ARR), net present value (NPV), profitability index (PI) and modified internal rate of return (MIRR) were evaluated for the different water volumes (up to 100 m³) assuming project life to be 10 years. The economic analysis revealed that a goldfish RAS with rearing tank capacity 20 m³ onwards can be feasible with a payback period less than 4 years, accounting rate of return 54%, net present value of Rs 241820 and modified internal rate of return of 23%. Sensitivity analyses revealed that market price of fish was most sensitive followed by survival rate, labour, maintenance, FCR, initial investment, discount rate, electricity cost and feed cost respectively. Interestingly, feed cost was found to be the least sensitive one.