Use of live and dead probiotic cells in tilapia Oreochromis niloticus

ABSTRACT:   To investigate the effect of live and dead probiotic cells on the non-specific immune system of tilapia Oreochromis niloticus , probiotics were introduced by feeding either in the form of live or dead cells, or supplying live cells to the rearing water in a closed recirculating system. The probiotics treatment enhanced non-specific immune parameters such as lysozyme activity, migration of neutrophils and plasma bactericidal activity, resulting in improvement of resistance to Edwardsiella tarda infection. Especially, oral administration of live cells seemed to be more effective compared with other probiotic treatments such as oral administration of dead probiotic cells and supply of live probiotic cells to the rearing water. These results indicate that probiotics treatment is promising as an alternative method to antibiotics for disease prevention in aquaculture, and the viability of probiotic bacteria is a key factor to induce more potential effect of probiotics used for fish production.     

The optimum dietary docosahexaenoic acid level based on growth and non‐specific immune responses in juvenile rock bream,Oplegnathus fasciatus

A feeding trial was conducted to determine the optimum level and effect of incremental dietary levels of docosahexaenoic acid (DHA, 22:6n‐3) on growth and non‐specific immune responses in juvenile rock bream, Oplegnathus fasciatus. A basal diet without DHA supplementation was used as a control, and six other diets were prepared by supplementing with 4, 8, 12, 16, 20 or 40 g kg^?1 DHA. These diets included no eicosapentaenoic acid and/or arachidonic acid contents. The actual DHA concentrations of the diets were 1, 4.8, 8.9, 13.1, 17.6, 21.2 and 41.4 g kg^?1 diet (DHA_1.0, DHA_4.8, DHA_8.9, DHA_13.1, DHA_17.6, DHA_21.2 and DHA_41.4 respectively). At the end of feeding trial, final body weight, weight gain, specific growth rate and feed efficiency of fish fed the DHA_13.1, DHA_17.6, DHA_21.2 and DHA_41.4 diets were significantly higher than those fed the other diets (P < 0.05). The broken‐line analysis of weight gain indicates that the optimum dietary DHA level is 11.9 g kg^?1. Fish fed DHA_1.0 had the highest hepatosomatic index, an increase in plasma cholesterol, triglyceride, low‐density lipoprotein and aspartate aminotransferase levels, as well as a decrease in high‐density lipoprotein. Superoxide dismutase activity of fish fed DHA_13.1 and DHA_17.6 diets was significantly higher than that of fish fed DHA_1.0, DHA_4.8 and DHA_8.9 diets. Fish fed the DHA_17.6, DHA_21.2 and DHA_41.4 diets showed significantly higher lysozyme activity than those fish fed DHA_1.0, DHA_4.8 and DHA_8.9 diets. Therefore, the optimum dietary DHA level could be greater than 11.9 g kg^?1 but less than 13.1 g kg^?1 in diet.     

The growth of disk abalone, Haliotis discus hannai at different culture densities in a pilot-scale recirculating aquaculture system with a baffled culture tank

The growth rate of disk abalone, Haliotis discus hannai, energy consumption and changes in water quality were monitored in a pilot-scale recirculating aquaculture system (RAS) for 155 days. Baffles were installed in the RAS culture tanks to enlarge the attachment area and clean out solid waste materials automatically by hydraulic force only. The experimental disk abalones, of shell length 24.5 ± 0.5 mm, were cultured at three stocking densities, 700, 1300 and 1910 individuals/m² bottom area, in triplicate. The abalones were fed with sea mustard, Undaria pinnatifida, once a week. The abalone feed conversion rates and daily growth rates ranged from 24.5 to 25.9 and 0.32 to 0.36%, respectively. Their daily shell increments and survival rates ranged from 67.7 to 78.6 μm/day and 87.6–92.2%, respectively. The growth in weight tended to decrease at a culture density of 1300 individuals/m² bottom area, while shell increments and survival rates were acceptable at this density. The total power consumption for heating was 1185.4 kW, comprising 30.2% of the total power consumption, while the average water exchange rate was only 2.9% per day. The total ammonia nitrogen stabilized below 0.07 mg/L, after conditioning of the biofilter. The NO₂⁻–N, NO₃⁻–N and total suspended solid concentrations were also maintained within acceptable ranges for the normal growth of disk abalone. The use of the RAS with these newly designed culture tanks for disk abalone culture produced 1300 individuals/m² bottom area with a water exchange rate of only 2.9% per day and used about one-tenth of the heat energy of a conventional flow-through system.     

Existence of multiple isoforms of GnRH ligands and receptors in the dwarf gourami, Colisa lalia

GnRH (gonadotropin-releasing hormone) plays a pivotal role in the regulation of reproductive functions. We have identified genes encoding three GnRH precursors and three GnRH receptors (GnRHRs) in the dwarf gourami, Colisa lalia. All of their mRNAs were expressed in all the organs examined in the present study. The cloned GnRHR genes were divided into two distinct lineages: types 1 and 2.     

Flume tank and in situ trials for verification of static and dynamic methods for gear depth and underwater behavior of hairtail trolling lines

We investigated the underwater shapes of trolling lines for the improvement of hairtail fishing efficiency. Two sets of experiments were carried out, one on a small scale, where flume tank tests of four models were scaled down by a ratio of 1:10 and trolled at different speeds, and another at full scale, comprising a survey on board a commercial fleet. In situ trials were conducted off the coast of Jeju Island, South Korea, at 33°27′57.528″N, 126°55′48.846″E, a potential fishing ground for hairtail fishing. The full-scale gear was set by altering sinker weights whilst changing the length of the warp line at different towing speeds. A dynamic method using a mass-spring technique and full-scale gear was developed. External and internal forces that govern the motion of the gear were considered. A non-linear differential equation of motion was developed, solved by a fourth-order Runge–Kutta method at a time step of 5?×?10^?4 s for each trial. A static method was also developed using full-scale gear to predict the equilibrium gear configuration under all fishing conditions. The dynamic method better predicts the actual underwater performance of trolling line gear in real time.     

Lunar cycles and reproductive activity in reef fishes with particular attention to rabbitfishes

Cues from the moon influence synchrony in growth, feeding, migration, behaviour and reproduction of many reef fishes. Compared with comprehensive studies on the annual and daily activities of fish, few physiological studies have paid attention to the importance of lunar cues in reproductive activities. We review mutual and interesting relationships between fish reproduction and environmental changes induced by the moon, with particular emphasis on the reproductive activity of the rabbitfishes (Siganidae). Rabbitfish species exhibit, in nature, a definitive reproductive season, which differs among the tropical areas. During the reproductive season, synchronous spawning of rabbitfish is associated with a particular lunar phase. The lunar phase used by the respective species is similar in different regions on the earth. Histological observations revealed that gonads develop synchronously towards a peak around the spawning lunar phase, after which the gonads return to spent condition. Concomitant with gonadal development, sex steroid hormones were produced under the influence of gonadotropin (GtH). Injections of human chronic gonadotropin (hCG) to the fish that are undergoing active spermatogenesis accelerated testicular maturation. These results suggest that hormonal response in maturing the gonads in rabbitfish is under the regulation of GtH, and that pituitary secretion of GtH according to the lunar cycle accounts for the lunar rhythm in gonadal development. We speculate that the cues from the moon can be recognized by the higher parts of the hypothalamus–pituitary–gonadal axis. Possible relationships between exogenous environmental factors and the lunar‐reproductive rhythm are also discussed.     

Dissemination of antimicrobial resistant strains of Campylobacter coli and Campylobacter jejuni among cattle in Washington State and California

The purpose of this study was to investigate the genetic similarity of Campylobacter jejuni and Campylobacter coli with similar antimicrobial resistance phenotypes, isolated from cattle on different farms and at different times, in order to evaluate the possible existence of disseminated antimicrobial resistant clones. PFGE after SmaI and KpnI restriction identified 23 and 16 distinct PFGE patterns among 29 C. jejuni and 66 C. coli isolates, respectively. In C. coli, 51 (77%) of the resistant isolates demonstrated one of the four indistinguishable PFGE patterns, whereas only 24% doxycycline resistant C. jejuni shared one of the two indistinguishable PFGE patterns. The genetic mechanisms of resistance were homogeneous within and between these clonal types. Genetically indistinguishable (clonal) groups of C. coli accounted for most Campylobacter sp. with multiple antimicrobial resistance observed in this study, consistent with a role for clonal dissemination in the epidemiology of resistance in this species.     

Supplementation of Protein Hydrolysates to a Low‐fishmeal Diet Improves Growth and Health Status of Juvenile Olive Flounder,Paralichthys olivaceus

An 11‐wk feeding trial was conducted to evaluate three different protein hydrolysates as feed ingredients in high‐plant‐protein diets for juvenile olive flounder. Five experimental diets were fed to juvenile olive flounder to examine the effect of three different protein hydrolysates on growth performance, innate immunity, and disease resistance against bacterial infection. A basal fishmeal (FM)‐based diet was regarded as a high‐FM diet (HFM) and a diet containing soy protein concentrate (SPC) as a substitute for 50% FM protein was considered as a low‐FM diet (LFM). Three other diets contained three different sources of protein hydrolysates, including shrimp, tilapia, and krill hydrolysates (designated as SH, TH, and KH), replacing 12% of FM protein. All diets were formulated to be isonitrogenous and isocaloric. Triplicate groups of fish (15.1 ± 0.1 g) were handfed one of the diets to apparent satiation twice daily for 11 wk and subsequently challenged against Edwardsiella tarda. Growth performance and feed utilization of fish fed hydrolysate‐supplemented diets were significantly improved compared to those of fish fed the LFM diet. Dietary inclusion of the protein hydrolysates significantly enhanced apparent digestibility of dry matter and protein of the diets. In the proximal intestine, histological alterations were observed in the fish fed the LFM diet. The fish fed the hydrolysate diets showed significantly longer mucosal fold and enterocytes and greater number of goblet cells compared to fish fed the LFM diet. Respiratory burst activity was significantly higher in fish fed the TH and KH diets than fish fed the LFM diet. Significantly higher immunoglobulin levels were found in fish fed SH and KH diets compared to those of fish fed the LFM diet. Dietary inclusion of the protein hydrolysates in SPC‐based diets exhibited the highest lysozyme activity. Significantly higher superoxide activity was observed in groups of fish fed the KH diet. Fish offered the protein hydrolysates were more resistant to bacterial infection caused by E. tarda. The results of this study suggest that the tested protein hydrolysates can be used as potential dietary supplements to improve growth performance and health status of juvenile olive flounder when they were fed a LFM diet.     

Genetic characterization, morphometrics and gonad development of induced interspecific hybrids between yellowtail flounder, Pleuronectes ferrugineus (Storer) and winter flounder, Pleuronectes americanus (Walbaum)

Viable interspecific hybrids between yellowtail flounder (Pleuronectes ferrugineus, Storer) and winter flounder (Pleuronectes americanus, Walbaum) were produced by artificial insemination of yellowtail flounder eggs with winter flounder sperm. However, mean fertilization rate, hatching success and early survival up to 3 weeks post hatch were significantly lower than those of parental pure cross controls (P < 0.01). Overall, cytogenetic traits (karyological analysis and estimation of cellular DNA contents using flow cytometry) of hybrid flounder were intermediate between the two parental species. Microsatellite assay was used to distinguish the parental genomes in the hybrids; in most cases, one allele was specific to each of the parents. Morphometrics assessed by body proportions indicated that hybrids generally displayed a morphology intermediate between the maternal and paternal species. Interspecific hybrids exhibited abnormal and retarded gonad development in both sexes based on histological analysis of gonads from adult fish. The sterility of the hybrids presents a significant advantage for their use in aquaculture, as potential escapees would not be capable of reproducing in the wild and contaminating natural stocks.     

Feces Production and Ammonia Excretion of Pacific Abalone,Haliotis discus hannai,Fed Kelp,Laminaria japonica,in Relation to Water Temperature and Shell Length

Nitrogen excreted by aquatic animals mainly takes the form of metabolic wastes such as feces and ammonia, which is accumulated in the intensive aquaculture system and causes serious environmental contamination. So it is very important to determine the waste excretion characteristics of aquatic animals for the development of practical and nonpolluting land‐based aquaculture. Abalone has a unique feeding habit and feeding regime, different from those of finfish; abalone gnaw feed seaweed to produce feces and ammonia continuously. In this study, the rates of feces production and ammonia excretion of pacific abalone, Haliotis discus hannai, of three shell lengths (3, 5, and 7 cm) were investigated under three different temperature conditions (12, 16, and 20 C). All experiments were performed in triplicate in a semirecirculating aquaculture system. Feces were collected for 5 d, and ammonia concentrations (total ammonia nitrogen [TAN]) in the tank inlet and outlet were monitored every 4‐h interval for 24 h at the fourth day of the feces collection. The regressions for the weight‐specific feces production rate (g feces/kg abalone/d) and the weight‐specific TAN excretion rate (mg TAN/kg abalone/d) in relation to water temperature (T, C) and shell length (L, cm) were weight‐specific feces production rate = exp(1.575 ? 281.2/T² – 0.142L), r² = 0.9550, and weight‐specific TAN excretion rate = exp(5.052 ? 277.1/T² ? 0.136L), r² = 0.9598. Pacific abalone produced 108.3–111.7 g feces and excreted 3.83 g TAN/kg seaweed ingested (dry weight).