Feeding responses of juvenile shrimp Litopenaeus vannamei (Boone) fed at different frequencies under laboratory conditions

In shrimp farms, food partitioning during the course of the day is contradictory, ethology studies may help in determining the proper frequency. Litopenaeus vannamei juveniles were placed in 30 L aquariums (41 m⁻²), exposed to a 12:12 h light–dark cycle. Feeding was provided at 10% of biomass three, four and seven times per day, with observations made in 15 min h⁻¹ windows, initiated after the ration was offered. Latency to access the feeding tray and to start eating was recorded using instantaneous focal sampling and digestive tract filling (DTF) by the continuous focal method. Weight gain was recorded at the end of the experiment. We performed seven repetitions, with 28 individuals observed for 33 days for each treatment (490 h of observation). The three-times offering induced less latency for accessing the tray and for ingesting the feed as well as a higher DTF when compared with the other frequencies. Animals fed three and four times had similar weight gains, and were greater than those fed seven times. Our results indicate that a more spaced food offering stimulates the search for and ingestion of feed. As compared with other frequencies, the three-times-per-day option assumes lower labour costs and a more efficient use of the feed.     

Ecology,physiology and genetics of a phycodnavirus infecting the noxious bloom-forming raphidophyte <Emphasis Type="Italic">Heterosigma akashiwo</Emphasis>

Abstract:   Heterosigma akashiwo virus (HaV) is a large icosahedral virus (∼0.2 μm) harboring a double-stranded DNA (dsDNA) genome (∼294 kbp). The virus is the only member of the genus Raphidovirus in the family Phycodnaviridae. Since its first discovery, a number of ecologic, physiologic and genetic studies about HaV have been conducted; especially, the relationship between H. akashiwo and HaV in nature was studied and viral infection is now regarded as a significant factor influencing the dynamics and termination of H. akashiwo blooms. HaV infection has considerable impacts on H. akashiwo populations in both aspects of fluctuation in biomass (quantity) and changes in clonal composition (quality). Partial sequencing of the HaV genome revealed that a number of genes showed considerable similarity to those of other protist-infecting viruses; still, the phylogenetic position of HaV suggested a number of enigmas in host–virus coevolution. Here are summarized the ecology, physiology and genetics of HaV especially from the viewpoint of the host–virus relationship.     

Effects of silvering state on induced maturation and spawning in wild female Japanese eel <Emphasis Type="Italic">Anguilla japonica</Emphasis>

ABSTRACT:   The effects of silvering state of wild female Japanese eels Anguilla japonica on the success of induced maturation and the following spawning were examined. Thirty-eight females, collected in Mikawa Bay, were divided into four stages based on their silvering state: yellow (Y1), late-yellow (Y2), silver (S1) and late silver eels (S2). Despite injections of salmon pituitary extract (SPE) through the standard technique, Y1 and Y2 eels did not respond to the treatment with undeveloped gonad (gonad-somatic index [GSI]: 0.3–0.9), and all these females died by 5 weeks, probably due to an abnormal physiological condition. Most S1 (81%) and S2 eels (100%) matured completely (GSI: 17.8–51.4), and finally spawned successfully (69% for S1, 89% for S2). S2 eels fully matured with oocytes of over 750 μm in diameter by significantly smaller number of injections of SPE (5–6 times) than the case of S1 eels (6–8 times). The amount of eggs released by S2 eels (0.65 ± 0.11 g/fish per body weight [BW]) was significantly larger than those by S1 eels (0.54 ± 0.09 g/fish per BW). There was no difference in fertilization and hatching rates between eggs released by S1 eels and those of S2 eels. These results indicate that the success of induced maturation and spawning in wild female Japanese eels depends on their silvering state, and matured eggs can be obtained efficiently through the use of S2 eels rather than other stages.     

Induced thermotolerance and expression of heat shock protein 70 in sea cucumber <Emphasis Type="Italic">Apostichopus japonicus</Emphasis>

ABSTRACT:   Thermal limits, induced thermotolerance and the expression of heat shock protein 70 (Hsp70) in an echinoderm Apostichopus japonicus were studied. The sublethal and lethal temperatures for the juveniles were 30 and 34°C, respectively; a previous sublethal heat shock exposure (30°C, 2 h) could increase the survival rates of the sea cucumbers when they were exposed to 34°C. This induced thermotolerance could last for at least 2 days. Levels of Hsp70 increased substantially after sublethal heat shock exposure and linearly decreased with time. This result indicated that a close relationship existed between the induction of thermotolerance and the levels of Hsp70 in A. japonicus.     

Carbonic anhydrase and Na/K-ATPase activities at different molting stages of the giant freshwater prawn <Emphasis Type="Italic">Macrobrachium rosenbergii</Emphasis>

ABSTRACT:   In the present study, the role of carbonic anhydrase (CA) and Na/K-ATPase in the gill and epidermal tissues in the giant freshwater prawn Macrobrachium rosenbergii was examined as a function of molting stage. CA activity levels in the front and back gills were low at the intermolt stage C₀, but increased significantly at premolt stage D₃, and then decreased after molting. In the epidermal tissue, activity levels decreased gradually towards premolt to a minimum level at stage D₃, but became elevated at postmolt stages A and B. Na/K-ATPase levels in the front and back gills did not change significantly during the molt cycle. CA in the gill is possibly involved in supplying counter-ions for ion uptake, while CA in the epidermal tissue may play a role in mineralizing the exoskeleton after ecdysis. Na/K-ATPase in the gills may function in ion uptake from the ambient medium; however, since its activity was not influenced by the molt cycle, it probably does not have a major role in osmoregulation in the freshwater environment.     

Trawling for cephalopods off the Portuguese coast—Fleet dynamics and landings composition

Fleet dynamics was addressed for three cephalopod taxa of commercial interest, the squid Loligo vulgaris, the octopuses Octopus vulgaris and Eledone cirrhosa, and the cuttlefish Sepia officinalis, for 48 trawlers of the fish trawling fleet. Landing profiles (LP) were identified based on the species composition of the landings using hierarchical cluster analysis. Four out of a total of 12 different LP were related to cephalopods and other species associated with them.The effects on the landing proportions of a number of variables, year, season and vessel, are analysed for each of the species studied using generalized linear models (GLM). The factor “vessel”, including an ensemble of technical characteristics as well as the abilities of individual skippers, explained most of the model deviance, strongly reinforcing the existence of a fleet component dedicated to catch cephalopods. However, time also explains much of the variation found in the data.Seasonal alternation between landings of octopodidae and cuttlefish was observed within a small group of old trawlers operating mainly off the south coast, following the abundance cycles of these species. For a larger group of more modern trawlers, operating off the western coast, inter-annual shift between octopus and squid was found, together with a well marked seasonal pattern between the catches of cephalopods and horse mackerel.Spatial patterns of activity were identified using vessel monitoring system (VMS) data available for trawlers in Portugal, demonstrating the existence of cephalopod targeting strategies in Portuguese fish trawling activities.     

Anti-allergic effects of the brown alga <Emphasis Type="Italic">Eisenia arborea</Emphasis> on Brown Norway rats

To investigate the anti-allergic effects of the brown alga Eisenia arborea. A strain of Brown Norway rats know to strongly respond to immunoglobulin E (IgE) were used as an allergy model animal. The rats were immunized with ovalbumin by oral administration. The levels of serum IgE and histamine were suppressed in the rats fed a diet supplemented with dried E. arborea powder. As for the cytokine pattern, the interferon-γ production in the spleens and mesenteric lymph nodes (MLN) was enhanced, and the interleukin-4 (IL-4) production in the spleens and/or IL-10 production in the spleens and MLN were suppressed. These results, together with the change in the Th1/Th2 balance, indicate that the rats fed with E. arborea became more anti-allergic, suggesting that E. arborea might possess anti-allergic effects.     

Thermal stability of carp G-actin monitored by loss of polymerization activity using an extrinsic fluorescent probe

ABSTRACT:   The thermal stability of carp G-actin was investigated by monitoring loss of actin polymerization ability. To determine the amount of native actin remaining after heat treatment, actin was labeled with a fluorescence reagent, N-(1-pyrene)iodoacetamide. The loss of polymerization ability of carp actin during heat treatment, at between 45 and 55°C, occurred faster than that of chicken actin. The inactivation rate was influenced by concentrations of ATP and Ca²⁺ in solution. With the increase of Ca²⁺ concentration, the inactivation of carp actin was markedly suppressed. Furthermore, the activation energy of the inactivation of carp actin obtained from an Arrhenius plot was similar to that of chicken actin. These results indicated that the thermal instability of carp G-actin was due to the low affinites of ATP and Ca²⁺ for carp actin described in a previous report.     

Bioaccumulation of cadmium and its biochemical effect on selected tissues of the catfish (<Emphasis Type="Italic">Clarias gariepinus</Emphasis>)

The present study examines the pattern of accumulation of cadmium (Cd) and its biochemical effects on selected tissues of a variety of African catfish (Clarias gariepinus), after exposure to various doses of Cd. The results obtained indicate that at the end of 21 days of exposure, the total tissue organ cadmium concentration followed the pattern kidney > gill > liver > muscle for each of the exposure concentrations. The levels of Cd in these organs were higher than those in ambient water. Moreover, while the rate of uptake of Cd increased with time in the kidney, liver and muscle, it decreased in the gill. Superoxide dismutase (SOD) was significantly elevated only in the kidney of catfish treated with 0.2 and 0.4 ppm of Cd for 7 days compared with the control. Conversely, gill SOD was significantly decreased in the same concentrations of Cd-treated catfish relative to the control. Statistically similar levels of SOD were observed in the liver, brain and muscle with all the treatments after the same duration of treatment. In the fish exposed for 21 days, SOD activity was significantly decreased in the kidney with a corresponding increase in lipid peroxidation (LPO), but it manifested only with the 0.2- and 0.4-ppm Cd treatment relative to the control. In the liver, however, Cd exposure significantly increased SOD in the 0.2- and 0.4-ppm treatments of the same duration. In conclusion, the present study indicates that the accumulation of Cd and its effect on SOD and LPO in C. gariepinus is dependent on concentration, tissue and time