Effect of sub-lethal nitrite on selected haematological parameters in fingerling Catla catla (Hamilton)

A sub‐lethal nitrite toxicity trial was conducted using static conditions for a period of 96 h with fingerlings of Catla catla (21.4±3.6 g). Fingerlings were exposed to five concentrations of nitrite, that is, 1, 2, 4, 8 and 10.4 mg L^?1 and a nitrite‐free control to study changes in haematological parameters. Nitrite caused an increase in immature erythrocyte population (7–24%) in lower concentrations (0–4 mg L^?1) at 6 h while they were absent in higher concentrations. The total erythrocyte count was reduced at 6 h followed by an increase at 12 h with further reduction up to 96 h in all concentrations of nitrite. The 96‐h exposure resulted in 21.2–31.8% reduction in erythrocyte population in 1–10.4 mg L^?1 nitrite. The haemoglobin content decreased progressively with increasing nitrite concentrations as well as exposure periods. Total leukocyte count decreased initially at 6 h in all treatments followed by an increase after 12 h, signifying development of a protective response of the body to nitrite stress. Blood glucose decreased initially up to 24 h followed by an increase through 96 h. Serum protein level decreased continuously with increasing exposure period. The study revealed that exposure to nitrite caused changes in almost all the haematological parameters in the fingerlings depending on the concentration as well as exposure period. Nitrite being one of the important inorganic nutrients often recorded at higher levels in intensively cultured ponds, the present study highlights its adverse impact on fish and stressed the need for the management of this nutrient in culture ponds.     

Embryonic and larval developments of brackish water catfish,Mystus gulio (Hamilton and Buchanan, 1822) induced with human chorionic gonadotropin and consequent larval rearing

Mystus gulio, the long whiskers catfish, is a popular food fish and potential candidate species for aquaculture in Sundarban area of India and Bangladesh. Recently, catch of this species has declined due to overfishing and various ecological changes. In the present study, mature fish was induced to spawn in captivity through intramuscular injection of human chorionic gonadotropin at the doses of 10 IU/g to female and 5 IU/g to male. Photomicrographs of all developmental stages of live embryo and larvae were documented with the aid of a light microscope. Results demonstrated that morula, blastula, gastrula and neurula and organogenesis ended at 1:30‐, 3:00‐, 5:30‐, 7:30‐ and 17:15‐hour post‐spawning (hps) respectively. Heartbeat and muscular contraction of embryo commenced at 8:30 and 11.15 hps respectively. Hatching of embryo started after an incubation period of 17:30 hour at an ambient temperature of 29 ± 1°C. The newly hatched larvae measured 2.17 ± 0.29 mm in total length with a yolk volume of 0.165 ± 0.03 mm³ started feeding 36 hr after hatching. The present study, on induced breeding and chronological development of M. gulio embryo, will have significant implications on conservation and seed production for aquaculture.     

Effects of dietary protein on growth performance,nutrient utilization,digestive enzymes and physiological status of grey mullet,Mugil cephalus L. fingerlings reared in inland saline water

A 60 days feeding trial was conducted to illustrate the effect of graded levels of protein on the growth and metabolic enzymes of grey mullet (Mugil cephalus L.) fingerlings reared in inland saline water (ISW). Six isoenergetic (16 MJ/kg) and isolipidic (60 g/kg) diets containing 240, 260, 280, 300, 320 and 340 g crude protein (CP)/kg diet were formulated and fed to triplicate. Weight gain %, specific growth rate, protein utilizing efficiency, feed efficiency and RNA:DNA ratio were significantly higher (p < .05) in 320 and 300 g CP/kg diets. Fish fed with 240 g CP/kg diet showed significantly higher (p < .05) feed intake, whole‐body lipid content, hepatosomatic index value and liver glycogen content. Transaminase enzymes and malate dehydrogenase activities were elevated in fish fed 340 g CP/kg diet. Protease activity increased with increasing dietary CP level, but amylase activities showed an inverse relationship. No significant (p > .05) variations were observed for lactate dehydrogenase, oxidative stress enzymes, blood parameters and serum osmolality among all the treatment groups, but red blood cell count increases with increasing dietary CP levels. Based on the results, feeding dietary protein level of 300 g CP/kg is economically viable for rearing of grey mullet in ISW.     

Identification and pathogenicity study of emerging fish pathogens Acinetobacter junii and Acinetobacter pittii recovered from a disease outbreak in Labeo catla (Hamilton, 1822) and Hypophthalmichthys molitrix (Valenciennes, 1844) of freshwater wetland in West Bengal,India

The disease outbreaks in aquaculture system of wetlands are the major cause of fish mortality. Among various bacterial septicaemic diseases, fish mortality caused by Acinetobacter spp. is recently reported in different fish species. Fish disease outbreak was investigated in a wetland of West Bengal, India to identify the aetiological factors involved. The moribund fish were examined and subjected to bacterial isolation. Two bacterial causative agents were identified as Acinetobacter junii and Acinetobacter pittii by biochemical characterization and 16S rRNA gene amplification. Both the isolates were oxidase‐negative, nitrate‐negative, catalase‐positive and indole‐negative. The molecular identification using 16S rRNA gene sequencing and phylogenetic tree analysis further confirmed the two Acinetobacter spp. with 97%–99% similarity. The antibiotic resistance patterns of these two bacteria revealed that both of them were resistant to β‐lactam, cefalexin, cephalothin, amoxyclav, cefuroxime, cefadroxil, clindamycin, vancomycin and penicillin. In addition, A. pittii was also resistant to other antibiotics of cephams group such as ceftazidime and cefotaxime. In the challenge experiment, both A. junii and A. pittii were found to be pathogenic with LD₅₀ of 1.24 × 10⁵ and 1.88 × 10⁷ cfu/fish respectively. Histopathological examination of gill, liver and kidney revealed prominent changes supporting bacterial septicaemia. The investigation reports for the first time on concurrent infection by A. junii and multidrug‐resistant (MDR)‐A. pittii as emerging fish pathogens to cause severe mortality in Labeo catla and Hypophthalmichthys molitrix in a freshwater wetland.     

Fishmeal alternative from renewable CO2 for rainbow trout feed

The rapid global growth in fish farming and limited supply of fish meal (FM) has consequently reduced FM inclusion levels in compound feeds leading to a higher reliance on alternative protein sources. Sasya is a single cell protein (SCP) product that has a similar amino acid profile as FM. The aim of this study was to evaluate the effects of replacing FM with SCP on in vivo digestibility, growth, feed efficiency, whole‐body proximate/amino acid composition and gene expression levels of various hepatic enzymes in rainbow trout (Oncorhynchus mykiss). Three isonitrogenous (470 g/kg crude protein) and isolipidic (18 g/kg crude lipid) diets were formulated as follows: Diet 1: control (30% FM); Diet 2:24% FM + 6% SCP and Diet 3:18% FM + 12% SCP. Each diet was hand‐fed to triplicate tanks containing 30 rainbow trout fingerlings (4.99 ± 0.20 g) for 9 weeks. Apparent digestibility coefficients of SCP for dry matter, crude protein, lipid and energy were 60, 80, 93 and 74% respectively. Growth performance (final weight: 69–71 g), feed conversion ratios (0.91–0.94) as well as whole‐body protein and amino acid composition were unaffected by diets. However, Diet 3 significantly increased whole‐body crude fat and energy. Fish fed the SCP‐based diets had significantly higher expression for carnitine palmitoyltransferase‐1b (CPT1b), fatty acid delta 6 desaturase (FADS6) and fatty acid elongase 5 compared to the control. Overall, the quality of the SCP was similar as FM. Therefore, this product could enlarge the portfolio of alternative protein sources that can be used in fish diets and thus open a new market opportunity for use of a new feed resource in the feed industry.     

Cage‐pond integration of African catfish (Clarias gariepinus) and Nile tilapia (Oreochromis niloticus) with carps

Cage‐pond integration system is a new model for enhancing productivity of pond aquaculture system. A field trial was conducted using African catfish (Clarias gariepinus) and Nile tilapia (Oreochromis niloticus) in cages and carps in earthen ponds. There were four treatments replicated five times: (1) carps in ponds without cage, (2) tilapia at 30 fish m^?3 in cage and carps in open pond, (3) catfish at 100 fish m^?3 in cage and carps in open pond, (4) tilapia and catfish at 30 and 100 fish m^?3, respectively, in separate cages and carps in open pond. The carps were stocked at 1 fish m^?2. The cage occupied about 3% of the pond area. The caged tilapia and catfish were fed and the control ponds were fertilized. Results showed that the combined extrapolated net yield was significantly higher (P < 0.05) in the catfish, tilapia and carps integration system (9.4 ± 1.6 t ha^?1 year^?1) than in the carp polyculture (3.3 ± 0.7 t ha^?1 year^?1). The net return from the tilapia and carps (6860 US$ ha^?1 year^?1) and catfish, tilapia and carps integration systems (6668 US$ ha^?1 year^?1) was significantly higher than in the carp polyculture (1709 US$ ha^?1 year^?1) (P < 0.05). This experiment demonstrated that the cage‐pond integration of African catfish and Nile tilapia with carps is the best technology to increase production; whereas integration of tilapia and carp for profitability.     

Passive immunity in tiger shrimp (Penaeus monodon) fed with monoclonal antibody to white spot syndrome virus

A study was conducted on the stability of monoclonal antibody (MAb) in the hepatopancreas and hemolymph of Penaeus monodon and its effect on protection against white spot syndrome virus (WSSV) upon challenge. MAb C-5 raised against WSSV was purified and coated onto a commercial shrimp feed at dosages of 5, 10 and 15 mg/kg feed. The feed was fed to P. monodon and stability of the MAb in hepatopancreas and hemolymph was determined by immunodot and Western blot. Immunodot results indicated the presence of MAb for 2 h post-feeding in hepatopancreas and hemolymph which was dose-dependent. MAb was also detected in hemolymph by Western blot up to 1 h post-feeding. Shrimp fed with MAb were challenged with WSSV by oral and injection methods. In shrimp fed with 15 mg antibody/kg feed (0.45 μg MAb/g shrimp/day) WSSV infection significantly delayed both in oral and injection challenges with a survival of 65 and 70 % (p < 0.05), respectively, during 15 days post-challenge. MAb was stable in shrimp for passive immunization against WSSV and could be a potential tool for prophylaxis against the virus.     

Cryopreservation of dead fish spermatozoa several hours after death of Indian major carp, Labeo rohita and its successful utilization in fish production

Cryopreservation of semen collected from dead fishes showed that it is possible to use it for fish production. We humanely killed individuals of the Indian major carp rohu, Labeo rohita and stored at different temperature regimes of 31 °C, 0 °C, − 10 °C and − 30 °C till 8 h. At every one hour interval semen from these fishes were collected by Pasteur pipette and evaluated for sperm yield/kg body weight, motility, pH, spermatocrit (%) and sperm count. The semen having suitable characteristics such as; 70% spermatocrit or above and motility index of 4 or above was cryopreserved by following a specific protocol. The cryopreserved semen of the dead fishes was stored for 7 days and then thawed in a water bath at 37 °C for 50 s. It was found that up to 8 h, spermatozoa of rohu were viable when stored at 0 °C or − 10 °C. Sperm collected after 8 h of fish death and maintained at 0 °C was the best stored condition that showed 30% larval survival. The spermatozoa collected 8 h after fish death was mostly normal as observed under scanning electron microscope and the total length of rohu spermatozoa was 25-30 μm. The hatchlings produced with this cryopreserved semen grew normally and juvenile fishes of rohu could be produced. This study suggests that germ cells such as spermatozoa of dead fishes can be cryopreserved and utilized for restoration of a species. It has the potential use in cryo-conservation of endangered fishes, restoration of animals through fertilization and genetic manipulation studies.     

Effect of sewage sludge–coir pith pellets on dry matter yield and trace metal concentration in various plant parts of forage maize

Sewage sludge (SS), a highly heterogeneous semisolid fraction of sewage water (about 1% of the sewage water), contains various amounts of nitrogen (N) and phosphorus (P) as well as trace elements such as cadmium (Cd), lead (Pb), copper (Cu), nickel (Ni) and zinc (Zn) with extremely variable physical and chemical compositions. Application of SS improves soil properties, increases yield and simultaneously increases trace metal content in soil and plants. The difficulty in handling, transporting and applying SS and its adverse effect, especially trace metal content in soil and plant, can be overcome by SS–coir pith pelletization (SSCP) or mixing with sewage sledge–coir pith mixture (SSCM). A study was undertaken to evaluate the prepared SSCM and SSCP (1:1 ratio of SS and coir pith) along with SS on dry matter yield, trace metal content in soil and plant parts. The results showed that increased rates of application of SS or SSCM or SSCP increased the green and dry fodder yield of forage maize. Application of SS as either SSCM or SSCP at 1.2 and 2.4 g pot^?1 significantly reduced the trace metal content diethylene triamine pentaacetic acid (DTPA extractable) in soil and plant parts (leaves steam and root) compared to SS application. Therefore, in order to reduce the bioavailability of trace metal in soil and its uptake by plant, application of SSCM or SSCP at 1.2 or 2.4 g pot^?1 proved to be a better option than SS application.