Directional and Non-directional Movements of Bat Rays, <Emphasis Type="BoldItalic">Myliobatis californica,</Emphasis> in Tomales Bay,California

Synopsis The goal of this project was to determine if bat rays, Myliobatis californica, display oriented movements and are thus a viable model species for the further study of geomagnetic topotaxis in elasmobranches. We tracked one male and three female rays during September 1998 and August and September 2001 in Tomales Bay, California. The rays exhibited two modes of travel: (1) rapid and highly directional movements in a straight line along the length of the bay and (2) slow and non-directional movements within small areas. Directional movements were defined as point-to-point vectors in the paths of the bat rays that were oriented in similar directions, and the distribution of these was clustered rather than dispersed and uniform. Mean rates of movement during directional swimming approached 0.5 m s⁻¹. In contrast, vectors in the path of bat rays were at times oriented in varying directions, and a distribution of these was widely dispersed as we would expect if the rays were moving randomly. These were defined as non-directional movements. Oriented straight-line swimming is consistent with the species either being able to orient to the bathymetry of the bay or possessing a compass and (or) piloting sense.     

High-efficiency somatic embryogenesis and plant regeneration in California poppy, Eschscholzia californica Cham.

 The development of a rapid protocol for high-efficiency somatic embryogenesis and plant regeneration from seed-derived embryogenic callus cultures of California poppy (Eschscholzia californica Cham.) is reported. The optimized procedure required less than 13 weeks from the initiation of seed cultures to the recovery of plantlets and involved the sequential transfer of cultures onto solid Murashige and Skoog basal medium containing three different combinations of growth regulators. All steps were performed at 25  °C. Friable primary callus was induced from seeds of E. californica cultured on medium supplemented with 1.0 mg l⁻¹ 2,4-dichlorophenoxyacetic acid. The primary callus was transferred to medium containing 1.0 mg l⁻¹ 1-naphthaleneacetic acid and 0.5 mg l⁻¹ 6-benzylaminopurine to establish embryogenic callus and promote somatic embryogenesis. Regenerated plantlets were recovered after the conversion of somatic embryos on medium containing 0.05 mg l⁻¹ 6-benzylaminopurine and showed normal development. Embryogenic callus was induced at a frequency of 85%, an average of 45 somatic embryos were produced per callus, 90% of the somatic embryos converted, and about 70% of the plantlets were recovered in soil. The growth rate of somatic embryo-derived shoots could be increased by gibberellic acid treatment, but the resulting plantlets were hyperhydritic. Received: 14 February 1999 / Revision received: 27 April 1999 / Accepted: 14 May 1999     

Feeding and growth of the pearl oyster Pinctada margaritifera (L.) in Dongonab Bay,Red Sea

Plankton samples and gut contents of P. margaritifera were analysed monthly from April 1972 to March 1973. Coscinodiscus sp. was the most ingested food by pearl oysters of all ages. However, food variety increased as the oyster grew older. Experiments confirmed the absence of food selectivity in P. margaritifera. Unlike the young ones, the adult showed reduced growth during summer (July–September), which coincides with its spawning season.     

Residence time and habitat use of coho salmon in Humboldt Bay, California: an acoustic telemetry study

We monitored the movement of coho salmon (Oncorhynchus kisutch) smolts with acoustic transmitters from freshwater, through the freshwater/estuary ecotone, through the estuary, and to ocean entry to determine residence time and habitat use in Humboldt Bay, California. Tagged fish were monitored with a fixed receiver network and mobile tracking conducted from a boat. Coho salmon observed during the two-year study resided in Humboldt Bay beginning at least as early as late April and resided through the beginning of July. Coho salmon smolts spent more time in the freshwater/estuary ecotone compared to the lower estuary and spent an average of 10–12 days migrating to Humboldt Bay. Coho salmon smolts resided in Humboldt Bay, a marine embayment, for an average of 15–22 days prior to leaving the bay for the open ocean. Coho salmon smolts, as observed from mobile tracking, used deep channels and channel margins more often than floating eelgrass mats, pilings, and docks. In addition, tagged fish were more often detected in the central portions of Humboldt Bay characterized by deep channels with narrow intertidal margins. There were fewer detections in other portions of the bay characterized by shallow channels with large intertidal mudflats and eelgrass meadows. Relatively short transmitter life (70 days) precluded determining the latest date of coho salmon smolt residency in Humboldt Bay. In addition, tag size limited use to the largest emigrating smolts and may not represent the behaviors of the smaller-sized smolts which were more abundant.     

Food intake and growth in the blue-spotted trevally, Caranx bucculentus Alleyne and Macleay 1877, with reference to predation on penaeid prawns

Blue-spotted trevally, Caranx bucculentus , were fed different rations of pilchard and prawn in order to investigate feeding and growth relationships. Maintenance rations at 25.5° C amounted to 3.7% B.W. day⁻¹ and 2.7% B.W. day⁻¹ for prawns and pilchards, respectively. Additional feeding experiments at 28.9° C yielded a maintenance ration of prawns of 3.8% B.W. day⁻¹, suggesting there is very little if any temperature effect on the feeding-growth relationship over the range studied. Fish fed twice or more each day consumed about 7.3 ± 1.4% B.W. day⁻¹.
Given the biomass of this trevally in Albatross Bay, Gulf of Carpentaria, and the contribution of prawns to its diet, we estimate consumption of commercial prawns at 25 ± 5 g.ha⁻¹ day⁻¹ or 11 g kg⁻¹ day⁻¹.     

Comparison of Four Mendelian Loci of the California Sea Hare (Aplysia californica) from Populations of the Coast of California and the Sea of Cortez

Aplysia californica is a species widely used in neurobiology, and specimens are collected from a wide range of places along its distribution range. A. californica is endemic to the coast of California and the Gulf of California. On the west coast, this is an unusual distribution range relative to other benthic species from that region. Four polymorphic nuclear Mendelian markers were identified (three single-copy nuclear DNA loci and one microsatellite) for an initial survey of genetic variation of wild populations. F _ST values not significantly different from 0 (overall F _ST= 0.0148) suggest there was no geographic genetic population subdivision in 177 individuals examined. Received December 3, 1999; accepted March 3, 2000.     

Reduction of Reactive Distance and Foraging Success in Smallmouth Bass, Micropterus dolomieu, Exposed to Elevated Turbidity Levels

We determined how turbidity affected the reactive distance and foraging success of smallmouth bass, Micropterus dolomieu. Smallmouth bass reactive distance decreased exponentially with increasing turbidity, from 65cm in clear water to 10cm at the highest turbidity. Turbidity significantly decreased the probability of a fish reacting to a prey item, but did not influence foraging success following reaction to the prey. Elevated turbidity may reduce stream fish foraging efficiency and decrease prey consumption.     

池养大口胭脂鱼鱼种的食性

池养大口胭脂鱼鱼种的食性研究表明 ,大口胭脂鱼鱼种为浮游动物尺寸选择性鱼类 ,其选食行为主要受鱼体及水体中浮游动物的个体大小影响 ,与浮游动物的种类、逃跑能力、运动方式等关系不明显。并初步探讨了 3种浮游生物食性鱼类 (大口胭脂鱼、鲢、鳙 )的食物关系。     

Element Concentrations in Some Species of Seaweeds from La Paz Bay and La Paz Lagoon, South-Western Baja California, Mexico

La Paz Bay and La Paz Lagoon are water bodies of the Gulf of California that are influenced by waste water discharges from the City of La Paz and from activities of the phosphorite mining company “Rofomex”. Because seaweeds concentrate elements from the water and are used as effective indicators of contamination by metals, we investigated their usefulness in this region. Concentrations of certain major elements (Ca, Fe, K and Na) and trace elements (As, Ba, Co, Cr, Cs, Hf, Rb, Sb, Sc, Se, Sr, Ta, Th, U, Zn and Zr) were determined in 12 species of seaweeds from La Paz Bay and La Paz Lagoon using instrumental neutron activation analysis. The contents of trace elements of environmental importance (As, Co, Cr, Fe, Sb, Se and Zn) in all studied samples are within the range of typical levels for a pristine environment not subjected to anthropogenic impact. Somewhat higher concentrations of Cr (81mg kg⁻¹), Hf (4mg kg⁻¹), Rb (48mg kg⁻¹), Sc (6.3mg kg⁻¹), Ta (0.95mg kg⁻¹), Th (6.8mg kg⁻¹), U (33mg kg⁻¹) and Zn (90mg kg⁻¹) were found in the green seaweed species Ulva (formerly Enteromorpha) intestinalis, whereas such elements as As (77mg kg⁻¹), Sb (1.4mg kg⁻¹) and Se (1.8mg kg⁻¹) were mainly concentrated in the species Sargassum sinicola, Codium cuneatum and Padina mexicana respectively. Because of their higher abundance and heterogeneity in elemental composition the seaweeds species Ulva intestinalis and Caulerpa sertularioides seem to be more suitable for further biomonitoring of heavy metal pollution of the coastal waters in this zone.     

Food and feeding habits of four species of juvenile mullet (Mugilidae) in a tidal lagoon in Ghana

Juvenile mugilid fishes, Liza falcipinnis, L. dumerilii, Mugil bananensis and M. curema , which enter the Elmina Lagoon in the Cape Coast District of Ghana, have a similar diet comprising mainly bacteria, diatoms, blue-green/green algae, protozoans, detritus and particulate organic matter. No seasonal changes in the diet and feeding activity were observed. The relative gut length (intestine to standard length ratio) and diet showed no significant changes with size of fish in all the species. All four species were diurnal feeders, but their peak feeding times differed. Interspecific competition for food was possibly limited by species preferences for substrate particles of particular size range and differences in feeding chronology.     

Aerial and aquatic feeding in the silver arawana,Osteoglossum bicirrhosum

Synopsis The silver arawana, Osteoglossum bicirrhosum, hunts along shorelines and within flooded forests in the Amazon River basin and supplements its limited consumption of aquatic vertebrates by leaping from the water to obtain terrestrial and arboreal prey. We offered O. bicirrhosum prey both suspended above and submerged below the surface of the water. From high-speed digital recordings, we measured kinematic variables associated with the jaws, cranium, pectoral fins, and body during orientation and prey capture. Aquatic and aerial feeding events were kinematically distinct, with aerial events generally involving faster, larger movements and a distinct delay in the onset of lower jaw depression until the head had left the water. The comparatively large gape during leaping may facilitate prey capture by overcoming variability in the apparent position of the prey due to refraction, while the delayed onset of mouth opening may serve to reduce the effects of drag. This distinctive leaping behaviour allows exploitation of the terrestrial prey base, especially during seasonal inundation of the Amazon River basin when the aquatic food base is widely dispersed.     

Food habits of the smooth dogfish, Mustelus canis, dusky shark, Carcharhinus obscurus, Atlantic sharpnose shark, Rhizoprionodon terraenovae, and the sand tiger, Carcharias taurus, from the northwest Atlantic Ocean

Diet and feeding habits of the smooth dogfish, Mustelus canis, Atlantic sharpnose, Rhizoprionodon terraenovae, dusky, Carcharhinus obscurus, and the sand tiger, Carcharias taurus sharks, were investigated through analysis of stomach contents. Diet in M. canis was relatively homogeneous and was dominated by crustaceans, consisting mostly of rock crabs, Cancer irroratus. Diet in R. terraenovae was more heterogeneous and consisted largely of crustaceans and teleosts, in similar levels of prey importance. Use of cumulative prey curves as a measure of precision indicated that data were insufficient to fully describe the diets of C. obscurus and C. taurus. Nonetheless, these data suggested that both species are generalized feeders and consume a variety of teleost and elasmobranch prey. Further studies are necessary to fully characterize diet in these two species.