Salinity increases total body prolactin and gill and skin prolactin receptor expression in the Chinese edible frog,Hoplobatrachus rugulosus,tadpole

Water salinity has effects on growth and metamorphosis of anuran species, including Hoplobatrachus rugulosus. Previously, we reported that cultured H. rugulosus tadpoles at low salinities (2–4‰) were of bigger size and grew faster than those in fresh water (FW). However, at a higher salinity level of 6‰, their sizes were reduced and the metamorphosis was delayed. It was therefore hypothesized that high salinity‐induced osmotic stress affected secretion of prolactin (PRL), which acts as osmoregulatory hormone and a regulator of metamorphosis in amphibians. In this study, transferring tadpoles into 4‰ and 6‰ brackish water increased the PRL levels by ~1.2‐ and ~twofold, respectively, as compared to FW group. These osmotic challenges also increased the total body fluid osmolality and levels of Na⁺, Cl^? and Ca²⁺. The contents of triiodothyronine (T₃) were significantly reduced in 4‰ and 6‰ groups, but not 2‰ group. Three sizes (49, 29 and 23 kDa) of H. rugulosus PRL receptors (PRLRs) were detected, and their protein expression was found in the skin, gill, tail fin, brain, intestine, heart, liver and kidney. The expression of PRLR‐49k protein was significantly higher in both skin and gills in 2–4‰ groups, whereas that of PRLR‐29k and PRLR‐23k were higher in gills and lower in skin of the 6‰ group than FW group. In conclusion, salinity challenge, particularly 4‰ and 6‰, increased the levels of PRL, while decreasing the T₃ levels, which could explain why salinity markedly modulated growth, metamorphosis and survival of tadpoles.     

Effects of salinity on Brazilian flounder Paralichthys orbignyanus from fertilization to juvenile settlement

The Brazilian flounder, Paralichthys orbignyanus, is a promising candidate for aquaculture, especially due to the euryhalinity demonstrated experimentally for large juveniles (3 g) and sub-adults. Flounder are observed in estuaries and were already reared in fresh and salt water, however little is known with respect of salinity tolerance during their early development. The objective of this work was to evaluate the effects of salinity from fertilization to juvenile settlement. Three experiments were conducted to evaluate the effects of salinity. In trial 1 adult flounder were captured in the wild, transferred to the laboratory and induced to spawn. The gametes were hand striped, split in four samples and fertilized with water at 10, 15, 25, and 35‰. Eggs were considered fertilized when the first cell divisions were observed under the microscope. For the trial 2 newly hatched larvae were reared in four salinities (5, 10, 20, and 30‰) and their growth and survival were observed until metamorphosis. In trial 3 larvae and juvenile of different ages (6, 16, 30, 45, and 60 dah — days after hatching) were evaluated for their tolerance to fresh water. Although the fertilization rate was directly proportional to salinity, hatching was successful only in full salt water. Larvae did not survive in low salinity water (5‰) longer than 6 days, whereas growth was improved when larvae were reared at 20 and 30‰. Young larvae cannot survive in salinities below 4‰, but at 30 dah juvenile presented 100% survival in fresh water. The present findings demonstrate the need for high salinity water (30–35‰) for the successful reproduction and incubation of P. orbignyanus eggs. Flounder can be reared successfully at intermediate salinities (20‰) during larviculture, but at lower salinities (5 and 10‰) their survival and growth are impaired. However, immediately after flounder metamorphose into juveniles they survive even in fresh water, demonstrating the strong euryhalinity of this species even at early stages of development.     

Faster growth before metamorphosis leads to a higher risk of pseudoalbinism in juveniles of the starry flounder <Emphasis Type="Italic">Platichthys stellatus</Emphasis>, as suggested by otolith back-calculation

The mechanism underlying malformation during flatfish metamorphosis is not clear. Here, the relationship between growth before metamorphosis and the occurrence of malformation after metamorphosis was examined in individuals reared in a single tank. Otoliths of starry flounder Platichthys stellatus larvae were labeled with alizarin complexone before metamorphosis [12 days after hatching (DAH)]. The positive linear regression between the lapillus otolith diameter and body length at 12 DAH enabled the estimation of individual larval size after completion of metamorphosis. At 12 DAH, the average body length of the typical pseudoalbino juveniles was significantly greater (5.37 mm) than that of the normal juveniles (5.13 mm) (P < 0.01, n = 100). In addition, of the larvae that were estimated to measure less than 4.8 mm at 12 DAH, approximately 80% metamorphosed into normal juveniles, whereas more than 60% of the larvae that measured more than 5.4 mm became pseudoalbino juveniles. These results indicate that the larvae that grow rapidly during the first 12 days are more likely to become pseudoalbino individuals after metamorphosis.     

Effect of Salinity on Growth,Feed Utilization,and Survival of Tilapia rendalli Under Laboratory Conditions

ABSTRACT

Juvenile T. rendalli were evaluated for 10 weeks to determine the effect of salinity on growth, feed utilization, and survival in tanks. Fish weighing 3.94 ± 0.44 g were stocked into twelve 50-L rectangular tanks at 15 fish /tank. The fish were raised in three salinity levels (5, 10, 15‰, and freshwater as a control). There were three replicate tanks per treatment. After the feeding experiment, a digestibility trial was conducted for two weeks. After 70 days, fish in the 10‰ treatment grew significantly larger (P < 0.05) than those in 5‰, 15‰, and freshwater. T. rendalli cultured in 10‰ had significantly lower feed conversion ratios and higher feed conversion efficiency and protein efficiency ratios. Survival of the fish was significantly (P < 0.05) different and depended on salinity level. The apparent digestibilities of crude protein, fat, ash, and gross energy were significantly higher (P < 0.05) in T. rendalli cultured in the 10‰ salinity treatment. However, apparent digestibility of dry matter did not differ significantly (P < 0.05) between 10‰ and 5‰. The results obtained indicate that 10‰ is optimal for T. rendalli in tank culture.     

Salinity a significant environmental factor for Vibrio harveyi virulence in Fenneropenaeus indicus

The effect of ambient salinity on the haemolymph variables of Fenneropenaeus indicus and its susceptibility to Vibrio harveyi infection under salinity stress has been studied. Adult shrimps were acclimated to 5‰ (hypo osmotic), 25‰ (iso osmotic) and 35‰ (hyper osmotic) salinity levels and the animals were injected with a mid logarithmic culture of V. harveyi at sub lethal level and haemolymph parameters were analysed. Haemolymph proteins, intracellular superoxide anion production, phenoloxidase (PO), alkaline phosphatase (ALP) and acid phosphatase (ACP) activity were found to be at elevated level both at 5‰ and 35‰ post challenge. The haematological responses showed a progressive increase (P < 0.05) up to post challenge day 5 (PCD 5) followed by a considerable decline at all salinities with the lowest being at 35‰. The alterations in the variables were higher in shrimps held at 5‰. However, the V. harveyi infection was severe in animals held at 35‰. The reduction in the parameters could be correlated with the decrease in survival rate of shrimps at 35‰ with a concurrent increase in V. harveyi at this salinity. Multiple regression analysis revealed that ACP (P < 0.001), haemocyte protein HCP (P < 0.001) and PO (P < 0.05) could explain 91% variability in the shrimp survival. These parameters may be used as effective shrimp health indicators. It is evident from the study that ambient salinity alters the haemolymph variables, modulates the virulence in V. harveyi and makes the shrimps more vulnerable to infection at higher salinity. The virulence of V. harveyi is increased at 35‰ salinity as being evidenced from the high mortality at this salinity. The study emphasizes the importance of salinity as an important environmental factor both in terms of host susceptibility and virulence of the pathogen.     

Long‐term low‐salinity stress affects growth,survival and osmotic related gamma‐aminobutyric acid regulation in the swimming crab Portunus trituberculatus

A 30‐day experiment was conducted to investigate the effects of long‐term low‐salinity stress on the growth performance and osmotic related chlorine ion channel ligand regulation: gamma‐aminobutyric acid (GABA) content and GABA_A receptor‐associated protein (GABARAP) expression in Portunus trituberculatus. The salinity levels of both the control group and the experimental group were 30 and 12 psu respectively. After rearing for 30 days, the specific growth rate and survival rate were compared between the two groups, and salinity 6 psu was used to test the salinity tolerance. The results were as follows: (a) Both the specific growth rate and survival rate were significant lower in the experimental group (p < 0.05) after 30 days; (b) After challenge with salinity 6 psu for 72 hr, the crabs of experimental group had a 100% survival rate, whereas the crabs of the control group were all dead within 48 hr; (c) The content of GABA and the gene expression level of GABARAP in experimental group were significant different from control group (p < 0.05) after challenge via salinity 6 psu. In the control group, the GABA content increased rapidly from 9.96 ± 2.09 to 42.00 ± 5.94 µg/g; however, in the experimental group, it only increased to 27.82 ± 2.55 µg/g; the gene expression of GABARAP in the experimental group increased to the maximum at 24 hr, then decreased and stabilized at 48 hr, suggesting that GABA and GABARAP were trigged during the early stage of low‐salinity stress resistance.     

Effect of salinity and temperature on marine leech,Zeylanicobdella arugamensis (De Silva) under laboratory conditions

The high prevalence (80–100%) of the marine leech Zeylanicobdella arugamensis (De Silva) on cage‐cultured Asian sea bass Lates calcarifer (Bloch) led us to investigate the percentage of juvenile leeches hatched from deposited cocoons, survival of juvenile and adult marine leeches at different salinity and temperature. The results showed that the hatching percentage of juvenile leeches was highest at salinity of 30 ppt (32.5 ± 2.8%) followed by 20 ppt (18.0 ± 4.3%) and 10 ppt (12.1 ± 1.4%), respectively. It was found that the adult and juvenile leeches could live up to an average range of 4–7 days at salinity ranging from 10 to 40 ppt. The juvenile leeches were able to hatch at temperature ranging from 25 to 35 °C but unable to hatch at 40 °C. The survival period of adult and juvenile leeches ranged from 11 to 16 days at 25 °C, which was comparatively longer than 5–13 days and 10 h – 5 days at 27–30 °C and 35–40 °C, respectively. The study provided the information on the physical parameters of salinity and temperature which are most optimal for the marine leech Z. arugamensis to propagate.     

Effects of salinity level on the survival,growth, feed utilization,carcass composition,haematological and serum biochemical changes of juvenile Meagre (Argyrosomus regius) (Asso, 1801) grown in ground saltwater

A study was performed to examine the effects of salinity on water quality, fish performance, carcass composition and haemato‐biochemical parameters in juvenile meagre, Argyrosomus regius. Fish (5.0 g) were stocked in fibreglass tanks at four salinity levels: 8‰, 16‰, 24‰ and 32‰, and fed a pelleted diet (47/17 protein/lipid) for 56 days. Results indicated that the growth, feed utilization, carcass composition and haemato‐biochemical parameters of meagre gradually improved with the increase in salinity up to 24‰ and then significantly (p ≤ .05) decreased at 32‰. The survival per cent showed a significant decrease when A. regius exposed to 8‰ salinity. An improvement with 32%, 47% and 34.1% of FCR, protein productive value and energy utilization was detected at 24‰ compared with 8‰ salinity respectively. The highest content of protein and the lowest of lipids were recorded in fish carcass at 24‰ compared with the opposite trend at 8‰ salinity. The 24‰ salinity treatment exhibited the highest value of haemoglobin (4.9 g/dl) and the lowest ratio (0.73) of albumin/globulin. The serum total protein, albumin and globulin were significantly higher at 24‰ and 32‰ salinity than those at 8‰ and 16‰ salinity groups. These findings indicate that 24‰ salinity level might be the best for meagre.     

Effects of salinity and temperature on the growth and survival of New Zealand shortfin,Anguilla australis,and longfin,A. dieffenbachii,glass eels

The ideal water conditions for maximizing the performance of the nursery culture of glass eels harvested from the wild for aquaculture need to be determined for the New Zealand shortfin (Anguilla australis) and longfin (Anguilla dieffenbachii) eels. This study determined the survival and growth of glass eels reared under different temperature and salinity conditions in the laboratory. The growth and survival of shortfin and longfin glass eels reared in salt water (35‰) maintained at 25 °C was examined over 84 days from capture. The mean specific growth rate (SGR) was higher in shortfin [2.30±0.29% body weight (b.w.) day^?1] than longfin glass eels (1.52±0.06% b.w. day^?1), and survival was also higher in shortfin (76.0±4.16%) than for longfin glass eels (28.7±6.36%). A second experiment identified the effect of salinity (0, 17.5‰ and 35‰) and temperature (17.5 and 26.5 °C) on the acclimation, growth performance and survival of shortfin and longfin glass eels over a period of 84 days from capture. There was no incidence of mortality for either shortfin or longfin glass eels reared across all salinity treatments (0‰, 17.5‰ and 35‰) at 26.5 °C, while survival of shortfin and longfin glass eels reared at 17.5 °C was the highest in 17.5‰, followed by 35‰ and 0‰ treatments. Both temperature and salinity affected the SGR of shortfin glass eels, with the highest SGR observed for shortfin glass eels reared in 0‰ water maintained at 26.5 °C. In longfin glass eels, salinity alone had an effect on the SGR, with the highest SGR observed in glass eels reared in 0‰ water regardless of the water temperature (17.5 and 26.5 °C). In addition, the adaptability of glass eels to salinity was evaluated from the development and the physiological responses of gill chloride cell (CC) morphology. The number and size of CCs increased significantly with increasing salinity in both shortfin and longfin eels.     

The effects of salinity on reproductive development and egg and larvae survival in the spotted scat Scatophagus argus under controlled conditions

In the present study, we report the first successful instance of controlled reproduction in Scatophagus argus, which has recently emerged as a new aquaculture resource. The controlled reproduction process for S. argus was optimized with regard to salinity acclimation. Gonadal maturation was affected by salinity in both sexes. Levels of plasma 17β‐estradiol (E₂) and 11‐ketotestosterone (11‐kT) were salinity dependent and increased significantly with the duration of acclimation. Plasma levels of gonadal steroids were higher in fish held at 25‰ salinity. The highest gonadosomatic indices (GSI), 15.1 ± 1.6 in the female and 6.4 ± 1.2 in the male, were also observed at 25‰ salinity. Nevertheless, the optimal salinity for S. argus embryonic development and larval culture was 15‰. Thus, the salinity requirement for gonadal maturation and early development are quite different. The use of advanced reproductive technologies combining salinity acclimation and stimulation of luteinizing hormone‐releasing hormone analog (LHRH‐A₂) resulted in a fertilization rate of 83.2%–91.3% and embryonic survival rates of over 90%. Embryos of S. argus at the 2‐cell, blastula, gastrula and pharyngula stages were observed. Most embryos hatched after 21.0 hr of incubation at 28.0 ± 1.0°C. The development of larvae into juveniles was completed at 40–45 days posthatch (dph). In this study, we provide information about the controlled reproduction of S. argus and identify the optimal environmental parameters for S. argus embryonic and larval culture, with the aim of developing reliable reproductive techniques for its mass production.     

Impact of salinity changes on growth,oxygen consumption and expression pattern of selected candidate genes in the orange mud crab (Scylla olivacea)

Change in environmental salinity level is a major limiting factor for the aquaculture productivity because it imposes severe stress on organisms that in turn retards growth. The orange mud crab (Scylla olivacea) is an important coastal aquaculture species (farming is practised in 10‰–20‰ salinity levels) in Bangladesh. The present study was conducted to investigate the changes in growth, O₂ consumption and mRNA expression levels of five selected genes in the orange mud crab (S. olivacea) exposed to three different experimental salinity levels (0‰, 10‰ and 20‰) for three months. Crabs reared at 10‰ and 20‰, showed significantly higher (p < .05) growth performance and expression of growth regulatory genes (Actin and α‐amylase). The highest levels (p < .05) of O₂ consumption and expression of ion regulatory genes (Na⁺‐K⁺‐ATPase, V‐type H⁺‐ATPase and Diuretic Hormone) were obtained at 0‰. Moderate levels of growth and expression of selected candidate genes were observed at 10‰ treatment while the highest levels of growth and gene expression were obtained at 20‰ (control salinity). Strong interactions were observed between growth performance and expression of growth genes (R² = 0.81–0.91), and rate of O₂ consumption and expression of ion regulatory genes (R² = 0.83–0.93), implying that the selected genes are important candidates for growth and ionic balance in S. olivacea. Growth performance was found to be very low at 0‰ initially, after 30 days crabs showed better growth performance at this salinity level. It is thus inferred that orange mud crab individuals might require 3–5 days for acclimation to salinity stress but it can take at least 30 days for acclimation to regular growth. Results indicate that with proper acclimation, the orange mud crab (Scylla olivacea) can be farmed at low salinity conditions and possibly in freshwater condition.     

Rearing of the Pacific white shrimp,Litopenaeus vannamei in a biofloc system: The effects of different food sources and salinity levels

The present study assessed the effects of different types of feeds and salinity levels on water quality, growth performance, survival rate and body composition of the Pacific white shrimp, Litopenaeus vannamei, juveniles in a biofloc system. Shrimp juveniles (2.56 ± 0.33 g) were cultured for 35 days in 300 L fibreglass tanks (water volume of 180 L) with a density of 1 g/L in six treatments. Three sources of feed (100% formulated feed, mixture of 66.6% formulated diet and 33.3% wet biofloc, and 100% wet biofloc) and two levels of salinity (10 and 32 ppt) were considered in two control groups and four biofloc treatments. Water quality parameters in the biofloc treatments were significantly better than control groups (p < .05). The highest increase in growth performance and survival rate were obtained in salinity of 32 ppt and mixed feed sources. Analysing the proximate composition of body shrimp indicates an increase in lipid and ash levels in biofloc treatments, which was more evident in the salinity of 32 ppt. In addition, the proximate analysis of shrimp body showed significant differences between biofloc treatments and control groups (p < .05). The highest FCR was found in the treatment with salinity level of 10 ppt and fed only with floc. Overall, it was found that the artificial diet supplemented with biofloc at the salinity of 32 showed better performance in the juvenile stage of Pacific white shrimp.     

Effects of salinity on growth,nutrient composition,fatty acid composition and energy metabolism of Scylla paramamosain during indoor overwintering

Three salinities (4‰, 12‰ and 25‰) were selected to determine the effects of different salinities on the growth, survival, nutrition and energy metabolism of Scylla paramamosain during indoor overwintering. Growth performance (survival rate, condition factor, hepatopancreatic index, weight gain rate and specific growth rate), nutrient composition (ash, moisture, crude fat, crude protein and total nitrogen), fatty acids, energy metabolites (glycogen, glucose, triglycerides, cholesterol and lactic acid) and energy metabolic enzymes (hexokinase, pyruvate kinase, lactate dehydrogenase and succinate dehydrogenase) were measured and calculated. The results showed that S. paramamosain exhibited the best growth and survival at 25‰ and worst at 4‰ after overwintering. In addition to consuming crude fat, excess protein was also broken down to provide energy in the 4‰ and 12‰ groups. The content of unsaturated fatty acids in the 25‰ group was higher after overwintering. Glycogen and glucose consumption and triglycerides, cholesterol and lactic acid production were lowest in the 25‰ group. The activity of hexokinase, pyruvate kinase, lactate dehydrogenase and succinate dehydrogenase was highest in the 4‰ group and lowest in the 25‰ group. The activity of hexokinase, pyruvate kinase, lactate dehydrogenase and succinate dehydrogenase in the hepatopancreas was higher than in the muscle. In conclusion, S. paramamosain uses less energy, has more unsaturated fatty acids and has a higher survival rate at a salinity of 25‰ after overwintering. The results of this study provide helpful information the indoor overwintering S. paramamosain in aquaculture production systems.     

Effect of salinity on natural community and production of Litopenaeus vannamei (Boone), within experimental zero-water exchange culture systems

Recent efforts have been made to culture marine shrimp in systems operating under low or zero‐water exchange and with decreased water salinity. The aim of this study was to investigate the impact of various salinity levels on qualitative and quantitative characteristics of the natural community and, more particularly, ciliated protozoa, and compare this information with shrimp growth and survival. Tanks with 9‰ salinity were characterized by a higher pH, but also by a significantly higher concentration of chlorophyll a (Chl a) per weight of suspended matter (1.93 ± 0.72 µg Chl a/mg TSS) than tanks with 18‰ (1.29 ± 0.68 µg Chl a/mg TSS) or 36‰ (1.37 ± 0.61 µg Chl a/mg TSS) salinity. Concentrations of ciliates (max 6000 cells mL^?1) showed considerable fluctuations over the sampling period, reflecting the impact of water salinity, dynamic interactions between ciliates and their diverse roles within the shrimp production system. There was no significant difference between survival rates of shrimp reared at 9‰, 18‰ or 36‰, but decreasing salinity from 36‰ to 9‰ led to a significant decrease in final shrimp body weight (from 13.40 ± 0.26 g to 10.23 ± 2.72 g). Future work should address the potential of ciliates as an indicator of aquaculture water quality, as is currently being done in the wastewater industry, and the contribution of ciliates as food sources.     

Use of response surface methodology to study the combined effects of temperature and salinity on hatching and deformity of the hybrid grouper,Epinephelus fuscoguttatus (♀) × Epinephelus polyphekadion (♂)

This study seeks to identify the optimal combination of temperature and salinity for the embryo development of the hybrid groupers, Epinephelus fuscoguttatus (♀) × Epinephelus polyphekadion (♂), using the central composite design and response surface methodology. Results have shown that the low hatching rates of fertilized eggs and high deformity rates of larvae were the result of lower or higher temperature/salinity levels. The linear effects of temperature and salinity were significant in both hatching rates and deformity rates (p < .01). Similar results were observed in the quadratic effects of temperature and salinity (p < .01). Effects of temperature were positively related to salinity effects (p < .05). Salinity effects were more remarkable than temperature on hatching rates, but not the same on deformity rates. Model equations were established for temperature and salinity effects on hatching rates and deformity rates. A high coefficient of determination (R² > .97) was found for the adequacy and predictive capability of model equations, indicating that these models can be applied to prediction. The optimal combination of temperature and salinity was 27.58°C/30.94, which was derived from the statistical optimization approach. In this condition, the hatching rate was the highest at 85.73%, and the deformity rate was the lowest at 5.96%, with a high desirability function of 0.957. The results of this study can be applied to improve hatching and decrease deformity in future cultures of hybrid groupers.     

Effect of the photoperiod on the larval development,body growth and muscle cellularity of shi drum (Umbrina cirrosa L.)

Shi drum (Umbrina cirrosa L.) larvae were maintained under three photoperiod regimes: a natural photoperiod regime (16L:8D), continuous light (24L) and equal durations of light and dark (12L:12D) from the end of the vitelline phase to the end of the metamorphosis. Muscle and body parameters were studied at hatching and at 4, 10, 14, 39 and 55 days post hatching (dph). During the vitelline phase, the total body length growth was scarce, whereas the muscle grew significantly, being the hypertrophy of the main mechanism involved. Both the total body length and the hypertrophy were significantly greater at 16L:8D than in the rest of photoperiod regimes. At 10 and 14 dph, the greatest body length was reached at 16L:8D, followed by the 24L group, showing the 12L:12D group the lowest values. At 14 dph, the hypertrophy and hyperplasia were also higher at 16L:8D than in the rest of groups. At 39 dph, the highest values of body length were reached in both 16L:8D and 12L:12D regimes, this latter group reaching the highest values of hypertrophy, thus showing a compensatory growth when comparing with the previous stages. The end of the metamorphosis took place at 50–55 dph in all the groups, with 2.7–3.1 cm of body length (P > 0.05). At this stage, the transverse area of the white muscle was similar among the groups, but the greatest hypertrophy was reached at 16L:8D, whereas the highest hyperplasia was reached at 24L.     

Effects of the timing of initial feeding on growth and survival of loach (<Emphasis Type="Italic">Misgurnus anguillicaudatus</Emphasis>) larvae

The effects of delayed first feeding on growth and survival and starvation on the point-of-no-return of loach Misgurnus anguillicaudatus larvae were studied by evaluating morphometric characteristics under controlled conditions. Larvae began to feed exogenously at 3 days after hatching (DAH) and the PNR occurred between 9 and 10 DAH at 23 ± 1.0°C. The experimental design included a conventional feeding regime with initial feeding from 3 DAH as a control, delayed first feeding for 4, 5 and 6 DAH. Morphometric characteristics (head depth, body depth, eye diameter, mouth diameter, musculature height, total length and yolk sac volume) were evaluated under different initial feeding time (3, 4, 5 and 6 days after hatching). Loach larvae initiated first feeding at 4, 5 and 6 days after hatching achieved comparatively lesser growth performance in all morphometric characteristics than that of 3 days at the end of the experiment. By day 6, significant differences were observed between 3 and 6 days initial feeding larvae for all morphometric characteristics except eye diameter and mouth diameter. Similarly, significant differences were noticed between 3 and 5 days initial feeding. However, there were no significant differences in head depth, body depth, eye diameter, mouth diameter, and total length between 3 and 4 days initial feeding until 12 DAH. After 15 days rearing, significant differences in all morphometric characteristics appeared between 3 and 4 days initial feeding and followed to the end of the experiment. It was also observed that the yolk absorption in loach larvae was completed by 6 days irrespective of the differences in the initial feeding. The yolk volume of 4 and 5 DAH larvae initiated first feeding at 3 days (0.0125 ± 0.0015; 0.0077 ± 0.0009 mm³) had significant differences compared with yolk volume of larvae initiated first feeding at 4 days (0.0081 ± 0.0011; 0.0039 ± 0.0004 mm³), 5 days (0.0079 ± 0.0010; 0.0017 ± 0.0002 mm³) and 6 days (0.0082 ± 0.0011; 0.0016 ± 0.0001 mm³). Survival rates of four treatments were estimated daily for 30 days and significant differences were observed between the treatments at the end of the experiment. The final survival rate was higher when the loach larvae initiated feeding at 3 days (75.9%) when compared with 4 days (31.8%), 5 days (14.5%) and 6 days (6.4%). The present study suggests that the first feeding of loach larvae should be initiated at 3 DAH for achieving better growth and survival or else bad growth performance will engender if the first feeding is delayed.     

Joint effect of temperature,salinity and pH on the percentage fertilization and hatching of Nile tilapia ( Oreochromis niloticus)

Rested upon Box‐Behnken experimental design and response surface method, the joint effect of temperature, salinity and pH on the fertilization and hatching in Nile tilapia was studied under laboratory conditions. Results showed that the linear and quadratic effects of temperature, salinity and pH on fertilization and hatching were all statistically significant (P < 0.01). Interactions between temperature and salinity, and between temperature and pH on fertilization and hatching statistically differed from zero (P < 0.05). Interaction between salinity and pH on hatching was significant (P < 0.05), but nonsignificant on fertilization (P > 0.05). Regressions of fertilization and hatching towards temperature, salinity and pH were established, with the determination coefficient being 99.17% for fertilization and 99.79% for hatching, and could be used for prediction. By utilizing statistical optimization technique, the optimal temperature/salinity/pH combinations were attained: 27.6°C/9.3 ppt/7.5 for fertilization, at which the maximum fertilization was 87.7%, with the desirability being 92.11%; and 27.1°C/9.2 ppt/7.4 for hatching, at which the maximum hatching rate reached 81.2%, with the desirability as high as 96.74%. It could be said that the fertilization and hatching concurrently culminated at the 27.3°C/9.2 ppt/7.4 combination. It can be envisioned that the application of these results derived would give an impetus to the tilapia seed production efficiency and in turn to the development of tilapia husbandry.     

Effects of different salinities on amino acid profile in Artemia franciscana

The effects of different salinity levels, including 10–15, 30–35, 70–75, 110–115 and 150–155 ppt, were evaluated on survival and the body amino acids (BAA) of Artemia franciscana. The results were expressed as total essential (TE), non‐essential (NE) and total amino acids (TAA); also, the ratio of the TE to NE (ENAA) on days 3 and 13 of the culture is reported. The study of changes in Artemia BAA showed that with the increase in the water salinity, the TE, NE and TAA increased significantly on days 3 and 13 of the culture. However, the highest ratio of ENAA was observed in the 110 gL^?1 salinity treatment on day 3 (1.067 ± 1.25). Regarding the effects of different salinity treatments on the survival rate of Artemia, it was observed that, generally, an increase in the water salinity would reduce the survival rate of this species. This reduction was observed on day 3 of culture in the salinity treatments above 120 (66.66 ± 1.68%) and below 30 gL^?1 (89.66 ± 0.34%) and on day 13 of culture in the salinity treatments below 30 (11.86 ± 0.13%) and above 70 gL^?1. Basically, it can be concluded that A. franciscana culture at a salinity of 110 gL^?1 can lead to the biological enrichment of Artemia in terms of amino acid profile.     

Species‐specific communication systems in an introduced toad compared with native frogs in Australia

• 1. Lineage‐specific communication systems may offer innovative ways of targeting control measures at invasive species.
• 2. Recent work has identified such a scenario in invasive cane toads (Bufo marinus) in Australia: toad tadpoles flee from chemical cues derived from crushed conspecifics, and this ‘alarm pheromone’ reduces tadpole survival rates and reduces body size at metamorphosis.
• 3. Before this method can be applied in the field, however, the signal's specificity needs to be tested against a wide range of Australian frog taxa, especially tropical species sympatric with cane toads. A signal that affected native frogs as well as toads clearly would be of little use for toad control.
• 4. Laboratory studies on cane toads and nine native frog taxa from the wet–dry tropics of the Northern Territory (Cyclorana australis, C. longipes, Limnodynastes convexiusculus, Litoria caerulea, L. dahlii, L. nasuta, L. rothii, L. rubella, Opisthodon ornatus) show that toad tadpoles rarely react to chemical cues from crushed frog tadpoles, and that frog tadpoles rarely react to chemical cues from crushed toad tadpoles. Crushed toad tadpoles occasionally elicited low‐level attraction (to a potential food source) by frog tadpoles.
• 5. Overall, frog tadpoles were less responsive to chemical cues (either from crushed conspecifics or crushed toads) than were toad tadpoles. The low level of cross‐lineage reactivity is encouraging for the feasibility of using cane toad alarm pheromones to control this invasive species in Australia; the risk of collateral damage to sympatric native frogs appears to be minimal. Copyright © 2009 John Wiley & Sons, Ltd.