Effect of insulin in the diet on the growth of European eels (Anguilla anguilla L.)

The effect of oral administration of insulin, in various concentrations, on the growth of European eels (Anguilla anguilla L.) was studied. In order to determine whether the insulin penetrated through the stomach or gills to the blood system, 5 ml insulin, suspended in an 0.6% solution of NaCl, was inserted via the mouth of eels, and the insulin content in the blood measured by radioimmunoassay immediately, and at one and two hours after administration. A control group was given 0.6% NaCl alone. Significantly increased levels of insulin in the blood plasma were found in eels which received high insulin concentrations compared to the control group. Eels administered 20 ppm and 40 ppm insulin in the diet grew significantly faster than a control group fed a diet without insulin, and a group fed 5 ppm insulin.     

Apparent digestibility coefficient of protein sources for carp, Cyprinus carpio L.

The digestibility of various diet components as protein sources for common carp, Cyprinus carpio L., at 500–800 g was studied by using an inert marker in the feed and collecting the faeces by stripping. Protein in fish meal (83.8%) and soybean meal (69.8%) were significantly more digestible than that of poultry meal (47.2%). Energy digestibility tests gave the following results: fish meal 93.4%, soybean meal 74.7% and poultry meal 63.9%. It was evident that the ability of carp to digest proteins is very high, and that they can utilize proteins as the main component of their diet.     

Use of endoscopy for gender and ovarian stage determinations in Russian sturgeon (Acipenser gueldenstaedtii) grown in aquaculture

The Russian sturgeon (Acipenser gueldenstaedtii) is native to the Caspian Sea, the Black Sea and the Azov Sea. It used to breed in the main incoming rivers, until dam construction in the mid 20th century blocked upriver spawning migration. Aquaculture of Russian sturgeon has only recently begun, prompted by their declining populations in natural habitats and the rise in meat and caviar prices. However, information on their gonadal development and puberty under culture conditions is incomplete.

Because sturgeons have no external sexual dimorphism and there are no external markers for sexing, internal examination of the gonads must be employed for gender identification as well as to monitor their development. The present study describes endoscopic and histological observations of the gonads of young Russian sturgeons aimed at identifying gender and monitoring ovarian developmental stage in females up to the age of 6 years, when they enter their first puberty cycle, as well as at 7 years of age, when they have completed vitellogenesis, under culture conditions. This information, as related to fish age and size, is of vital importance to commercial farming of Russian sturgeon for caviar production and reproduction.

For gonadal observations in both sexes, we used an endoscopic system consisting of a 4 mm, 14 cm long cystoscope sheath incorporated with fiber-optic light transmission, connected to a halogen cold light source and a miniature videocamera with a control unit attached to a color monitor. This system allowed us viewing of the fish's abdominal organs, and to save pictures of selected areas of the gonads on a computer as the fish's personal record. Ovarian biopsies were taken in parallel for histology at typical stages of gonadal development.

Gender could be identified with this system as early as at 3 years of age and the sex ratio under culture conditions of females, males and unidentified gender were 55, 40 and 5%, respectively.

Not only did large differences occur in the developmental stages of female of the same age group, but also ovarian development was highly asynchronous at the early vitellogenic stages. In late vitellogenesis, at the “gray egg” stage (1600–2600 μm diameter), the oocytes were quite regular in size and color, and remained so until the final stages of maturity.

Our study suggests that endoscopy is an efficient method for both gender identification at an early age, and for determination of gonadal development stage in sturgeon aquaculture. The ability to see the whole intact gonads of anesthetized fish can reveal important management and research information, with minimal damage or stress to the fish.     

Sexual dimorphism in yellow European eels, Anguilla anguilla (L.)

Sexual dimorphism in yellow eels, Anguilla anguilla (L.). was studied to clarify the differences between sexes. The focus was on the relationship between length/weight and sex. Three samples of eels, grown in captivity in different places in Israel, were studied. Females were significantly lighter than undifferentiated eels in the length range 33-47 cm. The regression coefficient did not differ significantly between females and undifferentiated eels. Sex induction, by a single injection of human chorionic gonadotropin, resulted in a higher loss of body weight during differentiation into the female than into the male.     

Chemical control of maize late wilt in the field

Late wilt, a severe vascular disease of maize caused by the fungus Harpophora maydis, is characterized by relatively rapid wilting of maize plants before tasseling and until shortly before maturity. In Israel, the disease has become a major problem in recent years. The pathogen is currently controlled using cultivars of maize having reduced sensitivity. In an earlier work, we modified a molecular method for use as a diagnostic tool to evaluate disease progression in field-infested plants and showed that several fungicides suppressed H. maydis in vitro. Here, we examine the effect of different fungicides on disease progression in a contaminated maize field in the spring and summer of 2009 and 2010. The field was watered using a drip irrigation line for each row and the fungicides were injected directly into the drip line. One of the four fungicides tested, azoxystrobin, was highly effective compared with the control, inhibited the development of wilt symptoms and recovered cob yield by 100%. Although this is the first success in preventing disease symptoms in infested fields in Israel, the azoxystrobin treatment did not reduce the amounts of pathogen DNA in host tissues or delay its spread. Attempts to reduce concentrations of this fungicide or to apply it by spraying were less effective than the triple full dosage treatment. The presence of the pathogen in the host tissues of the successfully treated plants and its ability to undergo pathogenic variations are increasing the risk of pathogen resistance and the urgent need to develop new ways of controlling late wilt.     

A comparison of genetic relationship measures in strawberry (Fragaria × ananassa Duch.) based on AFLPs, RAPDs, and pedigree data

Nineteen of the major strawberry (Fragaria × ananassa Duch.) cultivars grown in the UnitedStates and Canada were examined for AFLP markerpolymorphisms. For the AFLP reactions, the EcoRI-ACC primer was used in combination with fourMseI primers (MseI-CAC, MseI-CAG,MseI-CAT, or MseI-CTT). Each set ofprimers produced 46–66 scorable fragments ranging insize between 50 and 500 bp. The polymorphic fragmentsproduced from each set of primers were more thansufficient to distinguish among all the cultivars,demonstrating the usefulness of AFLP markers forcultivar identification. Similarity coefficients werecalculated based on data from 228 AFLP markers anddata from 15 previously characterized RAPD markers. The RAPD markers had been specifically selected forfingerprinting purposes because they succesfullydistinguish 41 strawberry cultivars, including the 19cultivars analyzed in this study. Separatedendrograms were constructed based on analysis of theAFLP and RAPD marker data using a neighbor-joiningalgorithm. The dendrograms were compared and found tobe very different. Correlations between similaritycoefficients calculated from AFLP marker data,similarity coefficients calculated from RAPD markerdata, and coefficients of coancestry calculated frompedigree information were evaluated. Interestingly,a better correlation with the coefficients ofcoancestry was observed with the RAPD marker data thanwith the AFLP marker data.     

Evaluating innovative technologies for multistage fish growth processes: Case study of an eel (Anguilla anguilla L.) farm

A new method for evaluating innovative technologies for multistage fish growth processes was developed. An earlier economic model was adapted to meet the real-world requirements of a commercial eel (Anguilla anguilla L.) farm. The economic benefits of different innovative technologies at the farm level were evaluated where the technology included multiple production alternatives at various intensities and several growth stages. Data were gathered into “bio-economic” tables that take into account the biological parameters of each production alternative and the costs related to its development and implementation. The adjusted data were then divided into groups of production alternatives and feasible combinations of alternatives for each of three growth stages were evaluated to determine the best technology for the overall growth process. A computer program enabled us to enumerate all potential innovative technologies, collect information on biological parameters and costs by growth stage, and compare additional profit expected after implementation of each innovation. Results reveal the most profitable innovative technologies by growth stage for the 5-year eel culture. Comparison of the 10 best technologies shows that combining the alternatives with the best biological parameters for each growth stage does not necessarily result in the maximum additional profit for the farm.     

Quantitative Genetic Analysis of Traits in Avocado Cultivars *

This research is aimed at quantitative genetic analysis of several avocado traits and cultivars. The experimental material consists of our avocado breeding project in which data were collected from several crosses as well as selfings of cultivars. Parenthood was determined by isozymes and the seedling progenies were assessed for eight traits. A biometrical genetic approach for analysis of this breeding project is presented. Genetic profiles of the traits and cultivars were detailed by several characteristics: level of heterozygosity and dominance deviation, dominance of alleles, dominance direction, general evaluation of additive and non-additive genetic variance, maternal inheritance, and allelic differences among the various cultivars in major genes controlling the same quantitative trait. Five avocado cultivars: ‘Fuerte’, ‘Hass’, ‘Ettinger’, ‘Tova’, and ‘Rosh-Hanikra’, were characterized separately for each trait. Practical conclusions for the breeder regarding economically important quantitative traits are discussed.     

The effect of 3,3′,5-triiodo-L-thyronine and 17-α-methyltestosterone on growth and body composition of the glass stage of the eel (Anguilla anguilla L)

This study was undertaken to determine the influence of orally administered 3,3,5-triiodo-L-thyronine (T₃) or 17--methyltestosterone (MT) on growth and body composition of the eel (Anguilla anguilla L.) during the glass stage.Elvers receiving 20 or 40 ppm of T₃ in the food weighed significantly more (P < 0.05) than controls. However, after 61 days of treatment a dosage of 60 ppm was not efficacious.Terminal percentages of body protein were significantly lower (P < 0.05) in elvers that received 20 ppm or 40 ppm T₃ in their diets, than in the control. Crude body fat content was higher (P < 0.05) in elvers receiving 20 ppm (29% fat) or 40 ppm (28% fat), than in the controls (26% fat). Compared to the control, diets containing T₃ at 20 or 40 ppm increased the body glucose concentration.Glass eels fed a diet containing 1 or 10 ppm MT grew significantly more slowly (P < 0.05) than the controls.Total body protein content was higher (P < 0.05), but total body crude fat content was lower (P < 0.05) in elvers fed a diet with 1 or 10 ppm MT compared to the controls. Total body glucose concentration of elvers administered 10 ppm MT was significantly lower (P < 0.05) than that of the control groups.