Reproduction related immunoglobulin changes in rainbow trout

Annual changes in plasma immunoglobulin (IgM) levels were investigated in three strains of rainbow trout Oncorhynchus mykiss which have different spawning periods, i.e., September–October, November–December, and January, reared under constant water temperature and natural day length. Plasma IgM levels decreased during the spawning season in all strains tested. The IgM changes became reversed in response to significant increases in plasma testosterone (T) and estradiol-17 in females and T and 11-ketotestosterone in males. Though the IgM decline showed a connection with suppressed immunocompetence, since many mature fish caught fungal diseases, no clear differences were observed in the plasma IgM levels between infected and noninfected fish during the spawning season. Incidentally, plasma IgM levels in infection prone fish were higher than in noninfection prone fish prior to the spawning season, whereas coincident differences in the plasma steroid levels were observed. Immature fish reared under lower water temperatures showed lower IgM levels. The effect of water temperature may have to be considered when analyzing the defense mechanism during the spawning season in rainbow trout.     

Quality of farmed Atlantic cod: effects of season and storage

Farming of Atlantic cod makes it possible to supply cod throughout the year. The aim of this study was to investigate the effects of season and postmortem ice storage on the quality parameters of farmed cod. Farmed Atlantic cod were sampled from the same pen in the period February 2006–March 2007. Cod whole body and somatic weight, condition factors and hepatosomatic index were all affected by season, all decreasing during maturation and spawning in the winter. Muscle pH and water were influenced by season, increasing during maturation and spawning and then decreasing after spawning. Season also affected the colour of the fillet. There was a significant increase in whiteness post‐spawning and a decrease during the second maturation. Water‐holding capacity (WHC), levels of trimethylamine oxide and trimethylamine, as well as microbiological data, did not vary due to season. Muscle pH, water content, WHC and microbial counts increased during storage for all samplings.     

Effect of high water temperature on brain-pituitary-gonad axis of the red seabream during its spawning season

In the present study, we examined the effect of high water temperature on brain-pituitary-gonad (B-P-G) axis of a perciform fish red seabream, Pagrus (Chrysophrys) major during its spawning season (April-May). High water temperature negatively affected all levels in B-P-G axis and turned out to be the termination factor of the spawning season of this species.     

Preliminary Observations on the Reproductive Physiology of Female Orangemouth Corvina in Captivity

Seasonal changes In oocyte growth and plasma estradiol, testosterone, thyroid hormones and vitellogenin levels were monitored in three captive adult female orangemouth corvina Cynoscion xanthulus subjected to a condensed (8 mo) seasonal cycle of photoperiod and water temperature. Plasma concentrations of estradiol and testosterone began to rise when temperature increased to 28 C and photoperiod to 15 h light (midsummer conditions). This was accompanied by elevated circulating levels of vitellogenin and the appearance of vitellogenic oocytes (diameter > 100 μm). Estradiol concentrations and mean oocyte size increased concurrently during late summer conditions and were maximum during fall conditions, approximately 8 wk after the beginning of ovarian recrudescence. In contrast, plasma levels of thyroid hormones did not show any distinct seasonal changes. Gonadally recrudesced females contained several size classes of vitellogenic oocytes. Injection of these fish with a luteinizing hormone-releasing hormone analog (LHRHa) caused maturation and spawning of the largest oocytes (mean diameter of follicles × 2500 μm). Another group of vitellogenic oocytes had been recruited into this size class by 2 wk after the end of spawning, which suggests that this species is capable of repeated spawning during the reproductive season. Injection of LHRHa resulted in increased plasma levels of gonadotropin and repeated spawning over several days. LHRHa-induced final oocyte maturation, ovulation and spawning were preceded by increases in plasma levels of two teleostean maturation-inducing steroids, 17α,20β, 21-trihydroxy-4-pregnen-3-one (20β-S) and 17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-P₄). The results provide preliminary evidence that oocyte growth is stimulated in orangemouth corvina subjected to an abbreviated seasonal cycle in captivity under midsummer photoperiod and temperature conditions and is associated with seasonal increases in plasma estradiol concentrations and vitellogenin production. However, the relative importance of 20β-S versus 17α, 20β-P₄ in the control of final oocyte maturation in this species could not be determined from the results of the present study.     

Monthly variation of condition index,energy reserves and antibacterial activity in Pacific oysters,Crassostrea gigas,in Stansbury (South Australia)

This paper investigates the temporal responses of 2-year old Crassostrea gigas to environmental changes in Stansbury, South Australia from September 2005 to October 2006. A total of 360 oysters were grown in one-line baskets on the farm using six replicates that were sampled monthly. A range of environmental parameters were assessed and correlated against biological indicators for oyster condition, metabolism and antimicrobial activity. Food availability by chlorophyll a, was low throughout the study period (0.5–1.5 µg L^? 1) and was significantly correlated to phosphorus concentrations. The condition index and shell weight of oysters significantly increased over the year, with the condition index dropping after spawning but then recovering within one month. Significant temporal variation in energy storage and utilization were observed in different tissues over the year. Glycogen in the mantle tissue was influenced by reproduction and correlated to chlorophyll a levels, but not in the gill or adductor muscle. The mantle glycogen and gill protein reached the lowest level in February when spawning occurred and presented evidence for seasonal variation in oyster metabolic activity. However, mantle and adductor muscle proteins did not drop after spawning indicating that these proteins contribute little to gametogenesis. Hemolymph protein was negatively correlated to water temperature and chlorophyll a, reaching the lowest level during summer. Hemolymph antibacterial activity significantly decreased after spawning, implying that the period of post-spawning is critical for oyster health. This study revealed trade-offs in the energy budget between immune resistance, growth, and reproduction. The results indicate that in a lean water environment, spawning events significantly regulate metabolic and immune capacities of oysters and a second year of rearing increased meat and shell weight but not the shell length. These findings are applicable to the management and development of oyster aquaculture within temperate southern hemisphere.     

Enhancement of reproductive performances of Gangetic leaffish, Nandus nandus through up regulation of serum Ca2+ concentration, improved morphological alteration of liver and ovary with dietary polyunsaturated fatty acids

Incorporation of polyunsaturated fatty acids (PUFAs) as biofunctional compounds with feed is an effective way for gonadal maturation without any hazardous effects on animal health, and thus it is possible to save the vulnerable species from the danger of extinction. In the present study sperm quality, level of Ca²⁺ concentration in serum, histological structure of the liver and developmental stages of ovary of an endangered fish species, Nandus nandus were investigated for the confirmation of the positive effects of PUFAs in reproduction and gonadal maturation. Fishes were collected from Brahmaputra River, Mymensingh, Bangladesh. Treated group was fed 1 % squid extracted phospholipid supplemented diet that was mixed with silver carp fish muscle where as controlled group was fed the same except phospholipid. For histology of liver and gonads, samples were dehydrated, cleaned and infiltrated, embedded in paraffin wax and sectioned. After that, the samples were stained with hematoxylin and eosin. The photomicrographs of the stained samples were taken by using light microscope. In comparison with the control group, treated group exhibited higher gonadal maturation which resulted in spontaneous spawning. Treated female demonstrated advanced gonadal developmental stages in comparison with the controlled female during different months. During spawning season, lipid granules and normal morphological alteration were observed in case of treated fish liver, whereas less lipid granules with more histological alteration of liver were observed in control group. Serum Ca²⁺ concentration in treated female was found significantly higher (P < 0.01) in contrast to the controlled female during the breeding season which was an indicator of the augment of estrogen secretion during ovarian maturation. Better sperm quality, early maturation of oocytes, less histological alteration of liver hepatocytes and spontaneous spawning performances of PUFA-treated fish were as a result of the efficiency of PUFAs in enhancing maturation. The experiment suggests that supplementation of dietary PUFAs improve the spawning performances of fish.     

Seasonal shift in spawning of Atlantic cod (Gadus morhua L.) by photoperiod manipulation: egg quality in relation to temperature and intensive larval rearing

Commercial intensive fry production of Atlantic cod will be dependent on production of viable eggs independent of season. This can only be done by manipulation of maturation by photoperiod, but little is known about potential effects on egg characteristics and larval viability. In two cod broodstocks, maturation was successfully advanced or delayed 6 months compared with normal spawning season (March–April) by manipulation of photoperiod. The advanced broodstock spawned both in spring and autumn the same year. In two of the spawning tanks during autumn, ambient temperature was reduced after reaching 13.7°C during the first half of the spawning period. Egg quality and viability were monitored, and several egg batches were incubated, hatched and start‐fed for examination of growth and survival. Temperatures above 9.6°C resulted in significant reductions in fertilization and normal egg development. Concurrently, fractions of dead and unfertilized eggs increased with elevated temperature. Actual relative fecundity was not affected by temperature. Egg characteristics improved when temperature was controlled and lowered below 9.6°C. Occurrence of irregular spawners suggests that handling of broodstock fish should be avoided during maturation and spawning. Cod larvae originating from eggs of the advanced or delayed broodstocks were successfully reared beyond metamorphosis. Survival was 9.0–46.6% and 29.3% in green and clear water respectively. Survival correlated with both initial and average feeding conditions, but growth rate did not correlate with either of survival and feeding conditions. Specific growth rates (8.3–13.6% day⁻¹) is comparable with other intensive rearing trials with cod, but were lower than reported from nature‐like systems.     

Effect of low temperature rearing, using deep-sea water, on gonadal maturation of the short-spined sea urchin, Strongylocentrotus intermedius, in Rausu, Hokkaido

It has long been hoped that sea urchins could be served to visitors to seafood restaurants, hotels, and summer festivals in Rausu, located in the world natural heritage site ??Shiretoko,?? during the summer tourist season. However, to date this has not been feasible because of the sea urchin spawning season (July?CSeptember), during which the quality of the gonads, the edible part of the sea urchin, decreases due to maturation. In this study, we examined the possibility of suppressing gonadal maturation and maintaining high-quality sea urchin gonads by low-temperature rearing using deep-sea water. Unripe sea urchins captured before the spawning season were reared under two temperature conditions from June to September. In those groups reared at ambient temperatures (2.8?C19.6?°C), gametogenesis in both sexes progressed rapidly with increased temperature, and almost all sea urchins reached full maturity by late July. In contrast, in groups reared at low temperatures (2.1?C5.1?°C), gametogenesis progressed slowly and >60?% of the sea urchins did not reach maturity even by early September. The feeding experiment also revealed that feeding with live Saccharina diabolica could increase the gonadal volume efficiently under low-temperature rearing conditions. These results demonstrate that low-temperature rearing, supplemented with feeding, is effective in suppressing gametogenesis to allow for the harvesting of high-quality sea urchins during the summer tourist season.     

Plasma somatolactin levels in coho salmon (Oncorhynchus kisutch) during smoltification and sexual maturation

Somatolactin (SL) is a novel pituitary hormone recently characterized in several fish species. Structural analyses have shown that SL belongs to the growth hormone/prolactin family, and that it is a highly conserved protein. SL is synthesized by the periodic acid/Schiff-positive cells in the pars intermedia, but has an as yet unidentified function(s). We have recently developed a homologous radioimmunoassay for coho salmon SL and measured plasma levels of SL during two stages of the coho salmon life cycle, smoltification and sexual maturation. During smoltification, plasma levels of SL changed almost in parallel with plasma levels of thyroxine; levels increased as morphological indices of smoltification appeared and decreased as smoltification was completed. Following this period, SL levels remained low until the spring prior to spawning. In a separate study, plasma levels of SL were measured in sexually maturing coho salmon that remained in fresh water throughout their life cycle. During the year of sexual maturation, plasma levels of SL gradually increased from the spring onward, reaching peak levels at the time of spawning in November and December. These data are similar to those previously reported for sexually maturing coho salmon that were maintained in seawater prior to spawning (Rand-Weaver et al. 1992). Therefore, increases in plasma SL levels occurred in sexually maturing fish irrespective of whether they were maintained in fresh water or seawater. Peak levels at spawning were higher than those observed during smoltification. Possible roles for SL in metabolism and reproduction are discussed.     

3月龄草鱼种免疫器官组织学及其免疫后免疫基因的转录差异

为研究处于同一时期但养殖条件不同的草鱼(Ctenopharyngodon idellus)鱼体规格与发育状态间是否具有一致性,观察压塘3月龄草鱼与普通3月龄草鱼头肾、中肾、肠道和脾脏的显微结构,并对压塘3月龄草鱼与普通3月龄草鱼进行腹腔注射疫苗处理,实时荧光定量PCR检测免疫7 d后、14 d后各期草鱼头肾、中肾、肠道和脾脏中IgM与MHCⅠ的表达量。结果显示,压塘3月龄草鱼各组织发育较普通3月龄草鱼迟缓。压塘3月龄草鱼与普通3月龄草鱼在免疫后,头肾、中肾、肠道与脾脏中IgM和MHCⅠ的表达量均有上升,且IgM与MHCⅠ的相对表达量峰值均出现在普通3月龄草鱼免疫14 d后的中肾中(IgM为74.51倍;MHCⅠ为56.02倍。结果表明,草鱼出血病活疫苗可以增强草鱼头肾、中肾、肠道和脾脏中IgM和MHCⅠ的表达,且在3月龄时期进行注射免疫效果最佳。     

Reproductive periodicity of a Penaeus esculentus population near Low Islets,Queensland, Australia

Since a major expense in the aquaculture of prawns is the location of gravid females, an investigation into the spawning habits of a north Queensland population of P. esculentus was begun as part of a wider survey of the East coast penaeid populations. This 31-month survey revealed a period of high reproductive potential limited to the autumn for both the new season prawns just reaching sexual maturity and the remnants of the last season's prawn population. The autumn sexual maturation was followed by a quiescent period through early spring when maturation again proceeded to the spawning period in the following autumn. In fact, the new season prawns' rapid sexual and somatic growth in the autumn was repeated by both generations in the summer and early autumn during the 3-year study. The temporal coincidence of both sea temperature and rainfall patterns with both somatic and gonad growth was investigated.     

Variation in spawning responses, egg and larvae productions from induced rohu (Labeo rohita) during pre-monsoon and monsoon seasons: Relationship with hormonal changes and oocyte responsiveness during final maturation

Early induced spawning in captive rohu (Labeo rohita) often encounters with reduced spawning performances and devaluation of final product. The present study attempted to gain insight into the problems associated with poor performance of rohu during pre-monsoon spawning. A combination of sGnRHa and domperidone was used to induce final oocyte maturation (FOM) and ovulation in rohu during early (pre-monsoon, PM) and normal (monsoon, MN) spawning. The spawning performance parameters such as, spawning response, production and quality of egg and larvae showed significantly lower values (p < 0.05) in PM, when compared with MN spawning. The egg and spawn productions were recorded as 2.6 ± 0.05 and 2.41 ± 0.05 during the MN season, which were reduced by almost 50% in the PM season. Moreover the quality of egg and hatchling was devaluated significantly (p < 0.05) and exhibited higher percentage of mortality and abnormality in PM than those recorded in the MN season. The plasma concentration of carp gonadotropin (cGtH), 17β-estradiol (E) and 17α20β-dihydroxy-4-pregnen-3-one (DP) in relation to progress of FOM and ovulation at different seasons exhibited marked variation in hormonal profiles particularly in E and DP of PM fish. Higher initial plasma E (3.8 ± 0.3) and a distinct E peak clearly indicated the lack of transition from vitellogenic to post-vitellogenic stages that prevailed in PM rohu. Delayed DP and cGtH surge during FOM and ovulation resulted in longer latency period in spite of higher water temperature (31.5 °C) that prevailed during the PM period. In-vitro study on oocyte maturational competence (OMC) clearly depicted the lack of maturational competence in ovarian follicles during PM than MN in rohu. However priming the fish with purified carp gonadotropin (PCG) enhanced the acquisition of OMC in PM rohu in such an extent, that no marked seasonal differences (p > 0.05) in OMC were remained further, when compared with MN follicles. The PCG mediated acquisition of maturational competence was found to be dependent fully on new mRNA and protein synthesis in PM fish. The present study clearly demonstrated that the oocytes' unresponsiveness to hormonal induction was mainly responsible for reduced spawning performance in PM rohu, which could be ameliorated through PCG priming to achieve better spawning response in rohu during the pre-monsoon period. Thereby, the rohu fry production could be initiated successfully as early as May, allowing public and private hatcheries to produce larger age-0 rohu fingerlings ensuring reliable steady source of stocking materials for grow-out system earlier in the season.     

Delayed gametogenesis and spawning of sea bass (Dicentrarchus labrax L.) kept under different photoperiod and temperature regimes

The present work investigates the importance of day length and temperature in the control of reproduction of sea bass, as well as the effectiveness of LHRHa and HCG in inducing spawning out of season in this species. A controlled regime was produced and seasonal cycles with high components of temperature and photoperiod were extended from the summer solstice for at least 6 months, followed by a short photoperiod regime for 3 months before a new increase in these components. Natural spawning in the control fish occurred more frequently in mid February, although it was also observed in January and early March. Temperature manipulation delayed the spawning one month with respect to the controls, although some of the animals entered into gonadal regression. Photoperiodic manipulation delayed maturation for three months with respect to controls but it was necessary to perform hormonal induction of spawning. Although LHRHa and HCG were both applied, only intraperitoneal injections of LHRHa were effective in inducing spawning of sea bass out of season when the temperatures were 17°C. Dephasing between the annual changes in photoperiod in relation to the coordination of the different events of the sexual cycle of sea bass is considered.     

Changes in the immunostaining intensities of follicle-stimulating hormone and luteinizing hormone during ovarian maturation in the female Japanese flounder

The role of gonadotropin (GTH) in the reproduction of the Japanese flounder, Paralichthys olivaceus, was studied by assessing the changes in the apparent activity of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in the pituitary gland during gonadal maturation by immunohistochemical analyses. Corresponding changes in plasma levels of testosterone (T), estradiol-17β (E₂), and 17α,20β-dihydroxy-4–pregnen-3-one (DHP) were also studied. Reared fish at the early spawning to termination stages were sampled from May to August and wild fish at the previtellogenic to termination stages were caught at 3- to 4-week intervals between April and September offshore from the northern mainland of Japan by gill nets. The gonadosomatic index of the reared fish decreased from the early spawning stage to the termination stage, while that of the wild fish increased significantly from the previtellogenic stage to the early spawning stage and decreased thereafter. In the reared fish, the immunostaining intensities of FSH and LH were high during the spawning period, accompanied by high plasma levels of T, E₂, and DHP. In the wild fish, the immunostaining intensities of FSH and LH were low during the previtellogenic stage but increased during the maturing and spawning stages. These results indicate that both FSH and LH are likely associated with oocyte maturation in the Japanese flounder.     

大鳍鳠脑垂体和血清生长激素水平的季节变化

根据大鳍脑垂体匀浆和血清样品的稀释曲线与鲤生长激素（ｃＧＨ）标准曲线的平行性,采用鲤生长激素的标准品和抗血清（ＲＡＧ）测定了周年中几个不同时期大鳍脑垂体和血清样品的生长激素（ＧＨ）含量,发现脑垂体和血清中的ＧＨ含量均表现出明显的季节变化。脑垂体的ＧＨ含量分别在３月份和８月份出现两个峰。４～７月的繁殖期和１１～１月的越冬期间,脑垂体的ＧＨ含量很低,而且波动不大。受水温和光周期的影响,大鳍血清ＧＨ水平表现为从冬季（１１～１月）到春季（２～４月）逐渐上升,夏季急剧升高,到夏末（７月底）达到最高,一直持续到秋季。大鳍血清ＧＨ含量的变化与生殖周期密切相关,最低的ＧＨ含量出现在性腺静止期,其次为性腺发育期,再次为性腺成熟期,在产卵期急剧升高,最高为性腺退化期。     

Sperm quality analysis of normal season (NG) and out-season by photoperiod manipulation (PG) of male rainbow trout broodstock (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)

Sperm quality parameters in rainbow trout (Oncorhynchus mykiss) were investigated during normal season spawning (November–January) and out-season spawning (July–August) treated with artificial photoperiod manipulation. Normal spawning males (n?=?15) were kept in an open concrete pond under natural condition. Out-season spawning males (n?=?15) were treated with artificial LED light (50 lm/m²) in a closed concrete pond. In these two experimental groups, five fish were used in each of three spawning periods. The mean weight and body length of males (2?+ years, n?=?30) were 1213.43?±?39.43 g and 45.08?±?0.62 cm, respectively. Sperms were collected from July to August 2016 in the out-season spawning or photoperiod-manipulated group (PG) (water temperature 14.21?±?0.31 °C) and from December 2016 to January 2017, in the normal season spawning group (NG) (water temperature 8.81?±?1.03 °C). Volume of sperm, osmolality of seminal plasma, density of sperm, percentage of motile spermatozoa (MOT), curvilinear velocity (VCL), and duration of motility were measured for each male. Seminal plasma osmolality, density of sperm, and the motility of duration were 358.47?±?37.24 and 308.87?±?44.09, 4.37?±?2.10 and 9.8?±?1.56, and 8.8?±?2.42 and 24.6?±?6.76 in PG and NG, respectively. Fertilization rate was 37.79?±?9.37% and 94.51?±?1.33% in PG and NG, respectively. Sperm quality parameters showed significant differences in most of the cases (p?<?0.05) and fertilization rate at eyed egg stage (150–160 degree-days) was significantly higher in normal season spawning group than the photoperiod-manipulated group (p?<?0.05). Though the rate of fertilization was low in out-season, it was able to get enough gametes in summer using only artificial light having no changes in other parameters.     

Metabolic,behavioral, and locomotive effects of feeding in five cyprinids with different habitat preferences

Fish generally perform routine swimming behaviors during food digestion; thus, changes in swimming performance and adjustments to spontaneous behavior resulting from digestion can have important ecological significance for wild fishes. The effects of feeding on metabolism, spontaneous activity, fast-start escape movement, and critical swimming speed (U _crit) were investigated in five cyprinids with different habitat preferences, specifically the Chinese crucian carp (Carassius auratus), common carp (Cyprinus carpio), black carp (Mylopharyngodon piceus), Chinese bream (Parabramis pekinensis), and qingbo (Spinibarbus sinensis). Generally, species in still water exhibited increased feeding metabolism, whereas species in flowing water showed higher spontaneous activity and locomotion performance. Digestion had no significant effects on either spontaneous activity or fast-start escape movement in the five cyprinids. These results could be due to the small meal sizes (approximately 2% body mass) and active foraging modes of cyprinids. The changes in aerobic swimming performance due to feeding were more complex. No effect of digestion on U _crit was observed in crucian carp (still water, high feeding metabolism, and low U _crit), common carp (widely distributed, high feeding metabolism, and high U _crit), and qingbo (flowing water, low feeding metabolism, and high U _crit), but digestion resulted in a significant decrease in the U _crit of Chinese bream (moderate feeding metabolism but high U _crit) and black carp (moderate feeding metabolism and low U _crit), suggesting no connection between postprandial U _crit changes and feeding metabolism (or between U _crit and preferred habitat). The maximum metabolic rate (MMR) of common carp and crucian carp increased after feeding, whereas the corresponding values for the other three cyprinids remained the same. The oxygen uptake capacity appears to meet the oxygen demand of both aerobic swimming and digestion in common carp and crucian carp, whereas qingbo sacrifices digestion for locomotion, and black carp and Chinese bream sacrifice locomotion for digestion under postprandial swimming conditions. The locomotion-priority mode of qingbo is adaptive to its active foraging mode in the demanding swimming habitat of rapidly flowing water, whereas the high respiratory capacities of postprandial crucian carp and common carp and hence the maintenance of their aerobic swimming performances might be a by-product of natural selection for hypoxia tolerance rather than for swimming speed.     

Role of high zinc levels in the stress defense of common carp

We studied the link between high zinc levels and the extreme stress tolerance of common carp. Fish under stress showed much higher plasma cortisol levels than controls. Stress or cortisol injection induced large changes in zinc levels in the common carp but not in grass carp, silver carp or tilapia. The effect of 5 days of anoxia and 4 subsequent days of recovery on cortisol and zinc contents in the common carp was investigated. Elevated plasma cortisol resulting from anoxia was correlated with decreased zinc in digestive tract tissue and increased zinc in the head kidney. Zinc was mobilized in the common carp while under stress. Changes in cortisol and zinc contents were reversible during the subsequent recovery from anoxia. Under stress, protein-bound zinc levels increased in the head kidney cell nuclei of common carp as cortisol increased. Zinc and cortisol were bound to the same protein, which was bound to DNA. The protein is likely a glucocorticoid receptor. An increase in immature red blood cells in stressed common carp was observed. Zinc was involved in the stress erythropoiesis response. Zinc may play an important role in stress defense in the common carp via the glucocorticoid receptor.     

Intensive polyculture of fish in freshwater ponds. I. Substitution of expensive feeds by liquid cow manure

In 1974 and 1975 nine experimental treatments of fish polyculture in stagnant water ponds without aeration were conducted at Dor. The polyculture was composed of common carp, silver carp, white amur (grass carp) and Tilapia. The treatments differed in stocking densities, feeding and manuring levels. The most productive treatment of the experiment, in which the fish were fed with protein-rich pellets, produced 50 kg/ha per day, probably a record for unaerated ponds of stagnant water. Two treatments (low and high stocking densities) fed exclusively with liquid cow manure produced an average yield of around 32 kg/ha per day. The yields of the treatments receiving high-protein pellets exceeded those of the treatments receiving grain pellets by 20 and 9.6 kg/day per ha, at high and low stocking densities, respectively, and in both cases the yield increments justified the extra cost of high-protein feed. The responses of the four fish species to the different levels of feeding and stocking densities were widely different. The common carp and white amur showed the greatest responses to increased feeding inputs while the silver carp and Tilapia, even at high densities, have done equally well at low feeding levels. Total body fat contents of the common carp were 20%, 15% and 6.2% when fed with high-protein pellets, grains pellets and liquid cow manure, respectively. Intermittent harvesting did not result in increased yields.     

Effect of d-Lys6 salmon sGnRH alone and in combination with domperidone on the spawning of common carp during the late spawning season

The effect of [d-Lys6] salmon gonadotropin-releasing hormone alone (sGnRH) and in combination with domperidone, a dopamine antagonist, on the spawning of common carp, Cyprinus carpio, was investigated during the late spawning season (when mature fish stop spawning under natural conditions when males and females are put together). Fish were induced to spawn by [d-Lys6]-sGnRH salmon gonadotropin-releasing hormone analogue (sGnRH-X) only when injected in combination with domperidone at doses of 10 g kg-1 and 20 mg kg-1 body weight respectively. [d-Lys6]-sGnRH-X alone did not induce spawning at a dose as high as 100 g kg-1 body weight. Fish injected with domperidone alone did not spawn either. These results demonstrate that [d-Lys6]-sGnRH-X in combination with a dopamine antagonist is effective in inducing spawning during the late spawning season.