Molecular cloning and characterization analysis of immunoglobulin M heavy chain gene in European eel (Anguilla anguilla)

In this study, the immunoglobulin M heavy chain gene of European eel (Anguilla anguilla) was cloned and analyzed. The full-length cDNA of the IgM heavy chain gene (GenBank accession no. EF062515) has 2089 nucleotides encoding a putative protein of 581 amino acids. The IgM heavy chain was composed of leader peptide (L), variable domain (VH), CH1, CH2. Hinge, CH3, CH4, and C-terminus and two novel continuous putative N-glycosylation sites were found close to the second cysteine of CH3 in A. anguilla-H1 and A. anguilla-H2. The deduced amino acid sequence of the European eel IgM heavy chain constant region shared similarities to that of the Ladyfish (Elops saurus). Atlantic salmon (Salmo salar), rainbow trout (Oncorhynchus mykiss), Grass carp (Ctenopharingodon idella), Common carp (Cyprinus carpio), Channel catfish (Ictalurus punctatus), and the orange-spotted grouper (Epinephelus coioides) with the identity of 46.1%, 39.7%, 38.9%, 32.4%, 32.3%, 31.7%, and 30.7%, respectively. The highest level of IgM gene expression was observed in the kidney, followed by the spleen, gills, liver, muscle and heart in the apparently healthy European eels. (C) 2008 Elsevier B.V. All rights reserved.

Observations on the nocturnal activity and feeding behavior of Anguilla japonica glass eels under laboratory conditions

Glass eels of the temperate anguillid species, Anguilla japonica, clearly showed a nocturnal activity rhythm under laboratory conditions. Light-dark cycle was a determinant factor affecting their photonegative behavior, nocturnal locomotor activity, and feeding behavior. Under natural light conditions, glass eels remained in shelters with little daytime feeding, but came out to forage during darkness. They moved and foraged actively in the following dark, and then their activity gradually declined possibly because of food satiation. They finally buried in the sand or stayed in tubes immediately after the lights came on. Under constant light, glass eels often came out of the shelters to forage in the lights but spent little time moving outside the shelters (e.g. swimming or crawling on the sand). Glass eels took shelter to avoid light and preferred tubes to sand for shelter possibly because tubes were much easier for them to take refuge in than sand. Feeding and locomotor activities of the glass eels were nocturnal and well synchronized. They appeared to depend on olfaction rather than vision to detect and capture prey in darkness. Feeding was the driving force for glass eels to come out of sand under constant light. However, in the dark, some glass eels swam or crept actively on sand even when they were fully fed. The lunar cycles of activity rhythms of glass eels that have been observed in some estuarine areas were not detected under these laboratory conditions.

Locomotor activity rhythm in the Japanese eel Anguilla japonica elvers

Under artificial LD cycles (6, 12, 18 L), the elvers of Japanese eel, Anguilla japonica, showed a 24 h cycle of locomotor activity rhythm being most active at light transitions: the eels' activity rose to a primary peak after lights-off, followed by a quiescent period during which they buried into the shelters or lying motionlessly on sand for most of the time, and then reached a secondary peak before lights-on. Elvers could resynchronize their activity rhythm with a new photo cycle within 4 d. Moreover, their activity level at dark phase significantly increased as the light period was prolonged: higher activity levels during shorter dark period. However, the elvers did not display clearly the existence of a circadian rhythm under constant light or dark conditions. The timing of daily activity rhythm evidenced in the Japanese eels may occur through the action of the LD cycles with a weak participation of an endogenous circadian system. In all the LD cycles, over 99% of the activity occurred in the dark phase, indicating that the eels were always nocturnally active no matter what time of day it might be. Under 12 L conditions, the eels' activity level and the time outside sand were significantly elevated both at light and dark phases as temperature increased from 10 similar to 15 to 20 similar to 25 degrees C. The activity rhythm pattern (i.e., two peaks occurring around light transitions) did not apparently change among temperatures. However, in contrast with the primary activity peaks immediately after lights-off at 20 and 25 degrees C, the timing of the primary peaks at 10 and 15 degrees C showed a latency of a few hours following lights-off, indicating the inhibiting effect of low temperature on the eels' activity.

Observations on the spawning behavior of artificially matured Japanese eels Anguilla japonica in captivity

Spawning behavior of artificially matured Japanese eels Anguillo japonica in captivity was investigated using a DVD Video image system. Following a routine hormone treatment technique for this fish, female eels were artificially matured by weekly intramuscular injections of salmon pituitary extracts (SPE) at a dosage of 40 mg kg(-1) BW for a total of 7-11 doses to induce ovarian maturation, while male eels received weekly intramuscular injections of human chorionic gonadotropin (HCG) at a dosage of 1000 IU kg(-1) BW for a total of 6-11 doses at 18 degrees C to induce testicular maturation in a separate aquarium. In this experiment, three pairs of such hormone-treated matured eels were acclimatized in seawater in 1.5 m(3) experimental aquaria with or without shelters at 20 degrees C for 24 h. Twenty four hours after the acclimatization terminated, the females received SPE injections to boost maturation and ovulation. Twenty four hours following these injections, the females received injections of HCG (1000 IU per fish, HCG injection) and 17 alpha-hydroxyprogesterone (2 mg per fish) to induce ovulation, while males were given HCG injections (1000 IU per fish, HCG injection) to induce spermiation. Video taping started after the 24 h acclimatization terminated and last for a total of 96 h. Before the HCG injections, both sexes were inactive, staying on the bottom or in shelters if available. Following these HCG injections, they became active and frequently left the bottom swimming in the water column. During the 24 h following HCG injections, activity accounted for 67% and 45% of the total activity in no shelter treatment for females and males, respectively, in comparison with 77% and 78% in shelter treatment. Activity was significantly more pronounced during this phase than during other phases for each sex in either shelter treatment. Egg release and sperm ejection occurred in the water column around the time eels' activity reached peaks. Eels either returned into the shelters or stayed motionlessly on the bottom of the aquaria after egg release and sperm ejection. Eight out of nine (89%) females in no shelter treatment spontaneously released eggs with a total of 11 batches 14-18 h following HCG injections, in contrast with four out of nine (44%) females releasing eggs for 4 batches 16-20 h in shelter treatment. Males arrived at activity peaks 11-13 h following HCG injections in no shelter treatment, 2-4 h ahead of the females (14-16 h), in comparison with 8-11 h in shelter treatment with 5-6 h ahead of the females (14-17 h). Courtship behavior indicative of spawning such as pairing, chasing and touching bodies was not observed in the eels in this study. However, on many occasions, eels of both sexes (male-female or female-female) were found to "cruise together" in water column for a short time period or frequently come together prior to releasing eggs and ejecting sperm, suggesting the possibility of group mating in artificially matured Japanese eels. (c) 2007 Elsevier B.V. All rights reserved.

Temperature influence on the spawning performance of artificially-matured Japanese eel, Anguilla japonica, in captivity

We studied the influence of temperature on the spawning performance of artificially matured Japanese eels, Anguilla japonica, in captivity. We used routine hormone injections to bring females and males to maturity in separate aquaria. We recorded the behavior of three pairs of such hormone-treated matured eels in an aquarium (2 replicates) at four temperatures: 14, 18, 22, and 27 degrees C, respectively. They became active and frequently left the bottom swimming in the water column, and spawning events occurred. Females released eggs in the water column around the activity peaks. Males preceded females in reaching activity peaks (presumably the timing of sperm ejection and egg release), possibly resulting in the low fertilization we observed in this experiment. Males and females returned back to the aquarium bottoms and became quiet after spawning. On several occasions, male-female or female-female pairs were observed to 'cruise together' in the water column for several to tens of seconds prior to egg releasing, but no courtship behavior indicative of spawning such as pairing and chasing was observed in the eels in our study. Our results suggest that 18-22 degrees C might be the thermal preference for spawning for Japanese eels, which approximates the temperature range of the 500 m deep water layer around the Mariana Islands seamount area, the presumed spawning site for the Japanese eel.

Survival of juvenile European eels (Anguilla anguilla) transferred among salinities, and developmental shifts in their salinity preference

After their oceanic migration, juvenile European eels Anguilla anguilla enter estuaries as glass eels, develop into pigmented elvers and migrate into fresh water. Fisheries often transfer such eels abruptly between salinities, principally glass eels and elvers from estuarine to fresh water. It is usually assumed that survival rates are high, but this required systematic investigation. Survival was found to be 100% over 21 days of glass eels and semipigmented elvers transferred abruptly from estuary conditions into fresh water, 50% sea water and full sea water. Fully pigmented elvers, however, showed significantly reduced survival when transferred into sea water. Salinity preference experiments with juvenile eels have historically been inconclusive. Here, in a choice chamber design, a clear developmental shift in salinity preference was found, with glass eels preferring 100% sea water, semipigmented elvers showing no clear preference and fully pigmented elvers preferring fresh water. We conclude that eel fisheries enhancement by abrupt transfer of juveniles among salinities is largely vindicated. In addition, developmental shifts in salinity preference have been clarified and this aids in the interpretation of eel migration patterns.