Sheenan Harpaz

Activity of intestinal mucosal brush border membrane enzymes in relation to the feeding habits of three aquaculture fish species

Abstract The activity of intestinal mucosal enzymes in various parts of the intestine and the pyloric caeca of adult fish from three different species was examined. Selection of the fish for the study was based on their aquacultural importance and the different feeding habits they exhibit: carnivorous hybrid striped bass ( Morone saxatilis × Morone chrysops ); omnivorous tilapia ( Oreochromis niloticus × Oreochromis aureus ) hybrids and herbivorous silver carp ( Hypophthalmichthys molitrix ). The results show marked differences among the different fish species corresponding to their feeding habits. Sucrase and maltase activities were found to be highest in the midgut of all species compared to other regions of the intestines. The lowest activity of γ-glutamyltranspeptidase (γ-GT) was found in the foregut of all species compared to other regions of the intestines. Alkaline phosphatase and γ-GT activities in the pyloric caeca of tilapia and bass were similar to those found in the intestines, indicating that these organs are an extension of the intestines where active protein degradation takes place.

Contradictory asymmetries in body and weapon size, and assessment in fighting male prawns, Macrobrachium rosenbergii

Asymmetries in weapon size and body size, both contributing to an animals fighting ability, may be contradictory in two fighting Macrobrachium rosenbergii males: One male may be larger in body size but smaller in cheliped size than its rival. The aim of the study was to determine the relevance of these two asymmetries in the assessment of relative fighting ability, and to reveal the effect of the asymmetry level on the structure of contests. Thirty contests were staged between male prawns from the ‘blue-clawed’ morphotype and the ‘orange-clawed’ morphotype. The blue-clawed males were 0%, 10%, or 20% larger in cheliped length but 93%, 45%, or 25% smaller in weight, respectively (n = 10), as compared to their orange-clawed opponents. The blue-clawed males with 10% and 20% advantage in cheliped length almost invariably won the contests. When similar in cheliped length, the 93% smaller blue-clawed males still won half of the contests. This indicated that the prawns ignored large asymmetries in body size even when no asymmetry in cheliped size existed. The results suggest that only cheliped size is used by M. rosenbergii males in the assessment of fighting ability. The effect of asymmetry level on contest structure was apparent only with the increase from 10% to 20% difference in cheliped size: Both the frequency and the intensity of fighting were lower in contests between prawns with 20% difference, as compared to 0% and 10% difference in cheliped length. Aggr. Behav. 23:81–91, 1997.© 1997 Wiley-Liss, Inc.

Comparative study of proteolytic enzymes in the digestive tracts of the european sea bass and hybrid striped bass reared in freshwater

Abstract 1. 1. A comparative study of the proteolytic activity in four different sections of the digestive tracts of the European sea bass (Dicentrarchus labrax) and hybrid striped bass (Morone chrysops × M. saxatilis) reared in freshwater revealed minor differences between these fish. 2. 2. Tryptic activity plays a major role in the proteolytic process in both fish. 3. 3. The activity of seven intestinal proteolytic enzymes was detected utilizing a combination of specific substrates and inhibitors. 4. 4. High levels of proteolytic activity were detected in both the proximal and distal sections of the fish intestine at a high pH range (9–10). 5. 5. In situ monitoring of pH levels revealed a lower pH level in the intestinal proximal section of hybrid striped bass compared with the distal section. 6. 6. In contrast, higher pH levels were detected at the proximal compared with the distal sections of D. labrax intestine.

Evaluation of Oreochromis niloticus×O. aureus hybrid progeny of different geographical isolates, reared under varying management regimes

Abstract Ten Oreochromis niloticus × O. aureus hybrids, progeny of different geographic isolates, were evaluated in polyculture with common carp, silver carp and grass carp. Traits tested included growth rate, survival, yield and proportion of males. The hybrid combinations O. niloticus ‘Nile’ (Egypt)× O. aureus ‘Mehadrin’ (Israel), and O. niloticus ‘Ghana-74’× O. aureus ‘Nile’ showed similar or better performance compared to the ‘Ghana-74’בMehadrin’ hybrid developed earlier at Dor. This suggests that the ‘Nile’ strains of both O. niloticus and O. aureus are potential candidates for commercial hybridization. The low proportion of males (30%) obtained with O. niloticus ‘Ghana-88’× O. aureus ‘Mehadrin’ crosses suggests that the later introduction from the Volta River differs from the 1974 introduction.

Culture of the Australian red-claw crayfish (Cherax quadricarinatus) in Israel: III. Survival in earthen ponds under ambient winter temperatures

Abstract The survival of the tropical crayfish Cherax quadricarinatus in earthen ponds under ambient winter temperatures was studied in the temperate zone in the central coastal plain of Israel. Four treatment groups in which sex and size were each tested at two levels were simultaneously run in four replicates over a period of 118 days (28 November 1996–26 March 1997). Minimum and maximum water temperatures were monitored every day, with minimum daily temperatures of under 10°C being recorded on six days. Overall survival was 60%; neither independent nor combined effects of sex and size on survival were found to be significant. Change in weight was minimal and few crayfishes entered baited traps, probably reflecting the reduced motor activity and feeding at low water temperatures. The economic implications of crayfish survival in earthen ponds under ambient winter temperatures, as well as the potential establishment of wild populations are discussed.

Effect of temperature and dietary l-carnitine supplementation on reproductive performance of female guppy (Poecilia reticulata)

Abstract The goals of this study were (1) to determine the optimal temperature for fry production by female guppy of two commercial strains (lyre tail and red cobra) and (2) to investigate whether dietary l -carnitine supplementation could help in alleviating reproductive problems associated with exposure to temperature stress. For the first goal, females were tested at temperatures ranging from 20°C to 32°C. Temperature was shown to have a significant effect on mean brood interval in both strains, but an effect on brood size was found only in red cobra. Best fry production was achieved at 25–27°C. A water temperature of 32°C caused increased female and fry mortality, degeneration of ovaries and reduced brood size. All surviving offspring at this temperature differentiated into males, but suffered from morphological abnormalities. For the second goal, females were tested at the optimal rearing temperature (26°C), and under high-temperature stress (32°C) and low-temperature stress (23°C). The parameters examined were brood size, brood interval and their quotient, and brood size/brood interval, which is the reproduction potential of the fish. Overall, l -carnitine supplementation at a dosage of 1100 mg/kg food, had no significant effect on brood interval or fry production efficiency.

Enhancement of growth in juvenile freshwater prawns, Macrobrachium rosenbergii, through the use of a chemoattractant

Abstract A feeding experiment conducted with juvenile freshwater prawns in which betaine was added as a feeding attractant, resulted in a 17% increase in growth of the group that had chemoattractant augmentation following actual feeding. The chemoattractant was added to the water, in an aqueous concentrated solution of 10 −3 M and induced a burst of food searching behavior leading to further consumption.

Effects of larger fish and size grading on growth and size variation in fingerling silver perch.

This study presents two experiments addressing growth and size variation in fingerling silver perch (Bidyanus bidyanus. In the first experiment, fish close to mean population size were raised either in the presence or absence of five larger fish for 60 days. Mean specific growth rate (SGR) and increases in the coefficient of variation and skewness were lower in the presence of larger fish, indicating a negative effect of large fish on the growth of smaller ones. In the second experiment, fingerlings were graded into groups smaller and larger than the median size of the population and raised in size-sorted groups of 60 large or small fish and mixed groups of 30 fish of each size category, for 60 days. There was no difference in mean SGR among groups, nor between the mixed group ad the weighted mean of the small and large groups. Biomass gain was higher in the mixed groups than in the weighted small-and-large groups, probably due to a slightly lower survival in the groups comprised of large fish. The fact that the effect of large fingerlings on the growth of smaller ones was evident in the first, but not the second, experiment may be attributed to higher size disparity between large and small fingerlings in the first experiment.

Effects of salinity and prolactin on gene transcript levels of ion transporters, ion pumps and prolactin receptors in Mozambique tilapia intestine.

Euryhaline teleosts are faced with significant challenges during changes in salinity. Osmoregulatory responses to salinity changes are mediated through the neuroendocrine system which directs osmoregulatory tissues to modulate ion transport. Prolactin (PRL) plays a major role in freshwater (FW) osmoregulation by promoting ion uptake in osmoregulatory tissues, including intestine. We measured mRNA expression of ion pumps, Na(+)/K(+)-ATPase α3-subunit (NKAα3) and vacuolar type H(+)-ATPase A-subunit (V-ATPase A-subunit); ion transporters/channels, Na(+)/K(+)/2Cl(-) co-transporter (NKCC2) and cystic fibrosis transmembrane conductance regulator (CFTR); and the two PRL receptors, PRLR1 and PRLR2 in eleven intestinal segments of Mozambique tilapia (Oreochromis mossambicus) acclimated to FW or seawater (SW). Gene expression levels of NKAα3, V-ATPase A-subunit, and NKCC2 were generally lower in middle segments of the intestine, whereas CFTR mRNA was most highly expressed in anterior intestine of FW-fish. In both FW- and SW-acclimated fish, PRLR1 was most highly expressed in the terminal segment of the intestine, whereas PRLR2 was generally most highly expressed in anterior intestinal segments. While NKCC2, NKAα3 and PRLR2 mRNA expression was higher in the intestinal segments of SW-acclimated fish, CFTR mRNA expression was higher in FW-fish; PRLR1 and V-ATPase A-subunit mRNA expression was similar between FW- and SW-acclimated fish. Next, we characterized the effects of hypophysectomy (Hx) and PRL replacement on the expression of intestinal transcripts. Hypophysectomy reduced both NKCC2 and CFTR expression in particular intestinal segments; however, only NKCC2 expression was restored by PRL replacement. Together, these findings describe how both acclimation salinity and PRL impact transcript levels of effectors of ion transport in tilapia intestine.

Dietary salt levels affect digestibility, intestinal gene expression, and the microbiome, in Nile tilapia (Oreochromis niloticus)

Nile tilapia (Oreochromis niloticus) is the world’s most widely cultured fish species. Therefore, its nutritional physiology is of great interest from an aquaculture perspective. Studies conducted on several fish species, including tilapia, demonstrated the beneficial effects of dietary salt supplementation on growth; however, the mechanism behind these beneficial effects is still not fully understood. The fish intestine is a complex system, with functions, such as nutrient absorption, ion equilibrium and acid-base balance that are tightly linked and dependent on each others activities and products. Ions are the driving force in the absorption of feed components through pumps, transporters and protein channels. In this study, we examined the impact of 5% increase in dietary NaCl on protein, lipid, ash and dry matter digestibility, as well as on the expression of intestinal peptide transporters (PepTs) and ion pumps (Na+/K+-ATPase, V-H+-ATPase, N+/H+-Exchanger) in Nile tilapia. In addition, effects on the gut microbiome were evaluated. Our results show that dietary salt supplementation significantly increased digestibility of all measured nutritional components, peptide transporters expression and ion pumps activity. Moreover, changes in the gut microbial diversity were observed, and were associated with lipid digestibility and Na+/K+-ATPase expression.