Higher Feeding Activity Research Articles

Zooplankton biomass, feeding and metabolism in a geostrophic frontal area (Almeria-Oran Front, western Mediterranean). Significance to pelagic food webs

Mesozooplankton abundance and physiological rates in copepods were measured at selected sites in the Alboran Sea, in May 1991, on Cruise Almofront 1 (JGofs-France). Higher total zooplankton standing stocks, higher copepod abundance, higher feeding activity by the latter and a higher proportion of phytoplankton-derived carbohydrates in their diet were found in the geostrophic jet of inflowing Atlantic water than in surrounding areas, which offered a range of oligotrophic conditions. Relationships with data obtained in other disciplinary fields on the same cruise show that biological enrichment was due to locally enhanced production rather than advection of exogenous living matter. In the most productive context, sustained production effected by phytoplankton cells in the > 10 μm class size (diatoms) was being significantly transferred to higher trophic levels through herbivores with a relatively long generation time (copepods). The processes responsible for the fertilization, and their relationship to the jet and its frontal boundary, are discussed.

Aspects of reproduction and diet of the long‐finned herring, Ilisha africana, off Cape Coast, Ghana

I. Africana off Cape Coast bred continuously throughout the year. The major breeding season was preceded by a period of high feeding activity, mainly on fish fry, penaeid shrimps and crustacean zooplankton.

Hybridization with Domesticated Rainbow Trout (Oncorhynchus mykiss) Reduces Seasonal Variation in Growth of Steelhead Trout (O. mykiss)

We tested the hypothesis that hybridization with domesticated rainbow trout (Oncorhynchus mykiss) reduces the seasonal variation in growth in both fresh and salt water in anadromous steelhead trout (O. mykiss). The seasonal variation in freshwater growth was more pronounced in the steelhead trout than in the hybrid and domesticated trout. Consequently, differences in growth rate among groups were considerably higher during winter than in fall or spring. We suggest that high feeding activity during unfavourable winter conditions in natural waters is maladaptive, but is not selected against in protected hatchery environments with a continuous food supply. This may lead to genetic divergence in feeding physiology and/or behaviour between steelhead trout and domesticated rainbow trout. Growth rates in experimental groups transferred to seawater in December relative to groups transferred in April were faster in rainbow and hybrid trout than in steelhead trout. The results support the hypothesis that seasonal variation in seawater growth in steelhead trout is reduced by crossing with domesticated rainbow trout.

Natural diet and feeding habits of the postlarval lobster Homarus americanus

Postlarval Homarus arnericanus were collected from Block Island Sound, Rhode Island, USA, during 5 die1 neuston sampling periods in summer 1988 and 1989. The foregut contents of the postlarvae were determined and compared with the relative abundances of potential prey groups in the plankton. Nine taxonomic prey groups were identified in the gut contents (N = 802). The composition of the prey groups and their relative frequencies of occurrence in the guts did not differ with time of day or sampling period. The frequent occurrence of copepods, decapod larvae, fish eggs and insect parts indicates a predominantly carnivorous feeding habit. Furthermore, the disproportionate frequency of occurrence of large copepod species and decapod larvae in the guts relative to their densities in the plankton suggests a preference for larger sized prey. Contrary to expectations, the mean gut fullness and condition of gut contents of individuals at different molt stages were not significantly different. Likewise, there was no significant difference in the incidence of guts with newly ingested prey between postlarvae in the premolt stages and those in the post and intermolt stages. Completely empty guts were rare. In addition, the variability in gut fullness and the condition of gut contents among individuals was high during all sampling periods. These indicate that postlarvae in the field forage successfully throughout the day. However, the significantly higher incidence of newly ingested prey in the guts of postlarval lobsters at night indicates a higher feeding activity during this time.

Feeding habits of immature chaetognaths in Tokyo Bay

Immature chaetognaths 2.8 mm long on average had the highest feeding activity at 22.00 h. The presence of diatoms in their guts is discussed.

Seasonal changes in feeding, fat body and ovarian conditions of Nezara viridula L. (Heteroptera: Pentatomidae)

Most dissected Nezara viridula (91.6%) from night catches had their stomach filled (half-full-full) with food, and females had a higher feeding activity than males. Females outweighed males at the ratio 1.3: 1, and an individual was heavier in October than in May. Ovarian development corresponded closely with decreasing fat body of females, and immature individuals had maximum fat in the abdomen. The spent individuals with empty stomach and fat thinly spread over the venter were relatively abundant in April and May, implicating the possibility of large-scale oviposition during these seasons.

Northern Adriatic Rocky Reef Fishes at Low Winter Temperatures

Abstract. The behavioural ecology of certain northern Adriatic fishes was observed from January to April at a water temperature of 7–11 oC. The fishes studied here do not migrate to deeper waters. Most of the benthic fishes show a similar distribution over the substrate in winter and in summer; in winter, however, they are very inactive and hide in the substrate. Suprabenthic fishes aggregate in littoral caves where they form dense, inactive, mixed aggregations. Certain hemipelagic and pelagic fishes join to form very dense aggregations at specific sites in the open waters of bays. Littoral predators display high feeding activity at a time when their prey is inactive. I present a hypothesis concerning possible implications of seasonally cyclic environmental temperatures for a sympatric community of non‐migrating fishes.

On feeding and behaviour ofOphiodromus flexuosus(Delle Chiaje) andNereimyra punctata(O.F. Müller) (Polychaeta, Hesionidae)

Abstract Food analyses and aquarium observations on Ophiodromus flexuosus and Nereimyra punctata from the Oresund, Denmark, and gut content analyses of O. flexuosus from Lindaspollene, west Norway, show that the species are carnivores and scavengers which search for food on the bottom. Small crustaceans and polychaetes are the most common prey; dead animals are utilized when encountered. The prey are swallowed whole. Most dissected specimens had food remains in the gut indicating frequent feeding during normal conditions. When prey are very abundant there is a high feeding activity. In search of food O. flexuosus creeps slowly about on the sediment surface. Living prey are detected from the movements, apparently through the vibrations set up in the water. Orientation is klinotactic, and the worm sneaks insidiously up on the prey until it attacks with a violent protrusion of the pharynx. N. punctata constructs a burrow system where it waits for passing prey, but it also makes excursions to the sediment sur...

A serological study of prey selection by Nephelopsis obscura Verrill (Hirudinoidea)

The prey range of Nephelopsis obscura was determined in three limnologically similar field sites using a serological technique. At each site the relative magnitude of utilization from highest to lowest was Chironomidae, Oligochaeta, Amphipoda, Copepoda–Cladocera, and Gastropoda respectively. When the three sites were compared, the relative proportions of these prey categories were shown to differ. Feeding activity was highest in the spring and summer and lowest in the fall and winter. Within each weight class of N. obscura, the Chironomidae, Amphipoda, and Oligochaeta were eaten most frequently. The Gastropoda and Copepoda–Cladocera were preyed upon more intensely by the smaller weight classes. The smaller (0–30 mg) and the larger (180−200+ mg) weight classes displayed proportionately higher feeding activity than the intermediate weight classes. Site-specific differences in weight class utilization of prey were recorded, indicating that generalizations on feeding activity of N. obscura are difficult to make even in similar field sites located in the same geographical area.

The role of food in the population dynamics of Orchesella cincta (Linné) (Collembola).

The feeding activity of the collembolan species Orchesella cincta (Linné) was studied in the laboratory and in the field. In the laboratory it was shown that at any one time only about 50-60% of the animals were feeding; the remainder were occupied with molting activities. Most of the time similar values were obtained in the field but during winter and during dry summer periods high percentages of empty guts could be demonstrated, indicating an absence or inaccessability of food. When favorable weather returned, a high feeding activity was again observed. Laboratory experiments and field observations indicate that temporary starvation periods are followed by synchronization of the molting and reproductive rhythms and an apparent increase in longevity. These phenomena are important for the restoration of the population after unfavorable periods but reduce the stabilizing force of food scarcity.

Constituents of the Cotton Bud. XIII. Further Studies on a Nonpolar Feeding Stimulant for the Boll Weevil123

The nonpolar feeding stimulant complex for Anthonomus Grandis Boheman found in the buds of cotton, Gossypium hirsutum L. (Deltapine Smooth Leaf), was fractionated and concentrated. Active fractions were extracted from buds and freeze-dehydrated bud powder with petroleum ether, chloroform, acetone, and chloroform-methanol. These fractions possessed widely different properties from those of the polar fractions studied previously. Silicic acid column chromatography produced a series of related compounds having the properties of the polar lipids. Thin-layer chromatography and countercurrent distribution studies produced compounds that were probably pheophytins. When pheophytins a and b were isolated from the bud, they gave high feeding activity after significant purification. Pheophytin a from spinach also gave modest activity, but cotton pheophytin a was inactive after hydrolysis and reesterification with phytol. These and previous studies of the polar feeding-stimulant complex suggest that a multicomponent system is responsible for optimum feeding activity of the boll weevil.