Digestive enzymes of eight Amazonian teleosts with different feeding habits

The levels of amylase, maltase, lipase and alkaline protease from eight fish species of the Amazon were analysed. The enzyme levels are not related to fish feeding habits, reflecting their ever-changing habitats and their opportunistic feeding behaviour.     

Ecological studies on crater lakes in West Cameroon The blood of endemic cichlids in Barombi Mbo in relation to stratification and their feeding habits

The West Cameroonian crater lake Barombi Mbo is stratified, with no detectable oxygen below 20 m. Of the endemic cichlid fishes in this lake Konia dikume is exceptional in having a mean haemoglobin concentration of 16.55 g/100 ml, while the other ten endemic cichlids range from 5.55 to 8.70 g/100 ml blood. The erythrocyte count is also higher in K. dikume than in the other species.
The phytoplankton in the lake is most abundant between 10 and 15 m from the surface.
The single species of cyclopoid copepod and the rotifers in the zooplankton remain in the top 20 m throughout the day and night, but the larvae of Chaoborus spend the daytime at depths below 20 m, mostly between 30 and 70 m. At night these larvae ascend into the upper layers, and feed on rotifers.
Konia dikume feeds on the larvae of Chaoborus , and the high concentration of haemoglobin in the blood of this fish, coupled with a large blood volume, appears to be an adaptation for the storage of oxygen. This would enable the fish to dive into the deoxygenated hypolimnion and extend the time available for feeding when the Chuoborus larvae are ascending at dusk and descending at dawn. Konia dikume appears to be a visual feeder, and in the short tropical twilight any extension of the feeding period could be of survival value.     

Histomorphological observations on the liver in some freshwater teleosts.

Histomorphology of liver is studied in six species of teleost viz., Heteropneustes fossilis, Clarias batrachus, Puntius ticto, Danio malabaricus, Nandus nandus, Chana punctatus. The liver is a bilobed structure usually reddish brown in colour. There are accessory liver lobes in H. fossolis and C. batrachus. The histological examination shows compact mass of oval or polygonel hepatocytes, blood sinusoids and reticuloendothelial cells. In addition several patches of pigmented hepatocytes are also noticed. After partial hepatectomy the changes in liver structure are shrunken nature of hepatocytes, enlarged blood vessels and accumulation of lymphocytes near the cut portion. After biliary obstruction with the help of ligation of bile duct hepatocytes become turgid in appearance within seven days. There is fibrosis of blood vessels as well as bile spaces. The turgidity of hepatocytes increases fifteen days after the ligation so much so that some of them show necrotic appearance. There are numerous bile thrombi noticed after biliary obstruction.     

Comparative histomorphology of the Mauthner cells in some freshwater teleosts.

The histomorphological observations are made on the Mauthner cells in eight species of teleosts belonging to six different families. The cells are better developed in Channa punctatus, Heteropneustes fossilis, Labeo rohita, Danio, malabaricus and Puntius ticto. They are symmetrically situated in Nandus nandus and are found to be absent in Mastocembalus armatus. Their position, shape and size vary in different species. The axon cap is well developed in Channa punctatus, Heteropneustes fossilis and carps. The cell body sends lateral and ventral dendrites besides several small dendrites. The lateral dendrite emerges through the axon cap, turns dorsolateral and becomes myelinated to form Mauthner axon. The Mauthner axon extends in the spinal region upto the caudal peduncle and forms synapses with the spinal motoneurons of the front column. There are numerous synapses and end bulbs from the vestibular fibres and VIIIth nerve distributed on the perikaryan of the Mauthner cell body. It is suggested that the Mauthner cells are comparatively well developed in those species in which the tail fin is better utilized for swimming.     

The activity of myofibrillar and actomyosin ATPase in the skeletal muscle of some marine teleosts in relation to their length and age

The activity of myofibrillar ATPase declined with length in the five species examined ( Merlanogrummus aeglefinis L., Merrluccius merluccius L., Physis blennoides Brunnich, Pleuronectes platessa L. and Merlangius merlangus L.). This decline was related to a decrease in the in vitro muscle contraction rate and appeared to be a scale rather than an age effect. Actomyosin was extracted from Merlangius merlangus L. to investigate the length related changes in the myofibrillar protein.     

Endogenous patterns of photomechanical movements in teleosts and their relation to activity rhythms

Summary The retinal rods, cones and epithelial pigment of most lower vertebrates display rhythmic photomechanical (retinomotor) migrations in response to changes in ambient lighting conditions. This study examines the extent of these migrations in the absence of the daily changes in illumination (constant darkness and constant light) in three species of teleosts. Salmo trutta, a crepuscularly active fish, showed two peaks of light adaptation occurring around dawn and dusk when kept in constant darkness. Tinca tinca, a nocturnal species, also showed an endogenous rhythm during extended periods of darkness, but, unlike Salmo trutta, it was light-adapted throughout what would normally have been day. At the maximal extent of migration under conditions of continual darkness, the pigment migrated 59% as much as it did during a normal light/dark cycle. Nannacara anomala, a tropical diurnally active species, showed a similar but more pronounced rhythm than Tinea tinea for all 3 days of experimental darkness, behaving essentially identically to fish exposed to a light/dark cycle. Nannacara anomala also displayed a weak rhythm when kept in constant light.It is concluded from these and previous results that the pattern of endogenous photomechanical movement depends both on the activity pattern of a species and on the constancy of the lighting conditions to which it has been exposed during its lifetime.     

The feeding habits of wolves in relation to large prey availability in northern Italy

We investigated wolf feeding habits in relation to the abundance of wild and domestic ungulates to test the hypothesis that large prey are preferred and that their abundance affects the use of other food categories and diet breadth. We determined diet composition by scat analysis from December 1987 to December 1992. The research was carried out in three study areas located in northern Italy and characterised by marked differences in wild and domestic ungulate abundance. In study area A (low wild and domestic ungulate availability) fruits, livestock, other vertebrates and wild ungulates made up the bulk of the diet (71% in volume). In area B (high availability of livestock) wolf diet was mainly based on sheep and wild boars (80% in volume). In study area C (high availability of wild ungulates) wild ungulates were the main food of wolves (90% in volume). Significant differences were found among study areas in the mean percentage volume of all food categories and in particular for wild ungulates, livestock, other vertebrates and fruits (p < 0.0001 in all cases). Diet breadth decreased in areas with high availability of large wild and domestic herbivores. The use of livestock species was lower where there was high abundance, richness and diversity of the wild ungulate guild. Selection for wild ungulate species was partially affected by their abundance: however other factors as prey social behaviour, adaptability to the habitat (for introduced species), and body size could have an important role in species selection by wolves. In particular in area C wild boars were selected for, roe and red deers avoided, and fallow deers and mouflons used as available. Livestock species were used in relation to their abundance and accessibility, in particular sheep were selected for and cattle avoided; but if calves bom in the pastures were considered as the only available cattle, they were selected for and sheep were used as available. Large and in particular wild herbivores were found to be of great importance for the wolf population maintenance in northern Italy, one of the most important recovery areas of Mediterranean wolves.     

Population genetic consequences of feeding habits in some forest lepidoptera

By surveying variation at allozyme loci in several phytophagous lepidopteran species (Geometridae), we have tested two hypotheses about the relationship of genetic variation to environmental heterogeneity: (1) that allozyme polymorphisms may exist because of associations between genotypes and "niches" (different host plants, in this instance), and (2) that the overall genetic variation of a species is correlated with environmental heterogeneity (or breadth of the species' overall ecological niche).—Genetic differentiation among samples of oligophagous or polyphagous species taken from different host species was observed in one of three species, at only one of seven polymorphic loci. The data thus provide no evidence for pronounced genetic substructuring, or "host race" formation in these sexually reproducing species, although host plant-genotype associations in a parthenogenetic moth give evidence of the potential for diversifying selection.—In a comparison of allozyme variation in polyphagous ("generalized") and oligophagous ("specialized") species, heterozygosity appeared to be higher in specialized species, at all polymorphic loci but one. It is possible that this unexpected result arises from a functional relation between breadth of diet and genetic variation.     

A note on the feeding habits of some uncommon sea stars

Natural history, aspects of aquarium behavior, and the first dietary data of three widely distributed, but relatively uncommon, Northeastern Pacific sea stars, Poraniopsis inflata (Fisher, 1906), Lophaster furcilliger (Fisher, 1905), and Cera-master patagonicus (Sladen, 1889) are presented. Our observations and analysis indicated P. inflata individuals ate sponges, while L. furcilliger ate sponges and chopped fish, and C. patagonicus appears to be a substrate surface deposit feeder. © 1993 Wiley-Liss, Inc.     

Morphological characterization of the alimentary tract of Antarctic fishes and its relation to feeding habits

Summary Morphological and morphometric characteristics of the alimentary tract in 22 species of carnivorous antarctic fishes were studied. It is shown that all of these species have similar, well-developed Y-shaped stomachs with generally thick (0.5–1.0 mm) walls. The relative stomach lengths are also similar, ranging from 9.8 to 22.2% of body length. Relative intestine lengths, a characteristic frequently used as an indicator of the kind of food eaten by a species, are also remarkably similar among most species (31 to 67%). Notothenia gibberifrons, a conspicuous benthos feeder, has a significantly longer intestine (91%), probably as an adaptation to the quantity of undigestible material (mud) incorporated with its faunal prey. These values fit within or below the limits (60–150$) of relative intestine length described in the literature for carnivorous fishes. The number of pyloric caecae is in general relatively low and fairly constant in each species. It is concluded that the morphological features studied could represent similar adaptations of these antarctic fishes to a similar carnivorous diet.     

Sialic acids in the salivary glands of some insects with different feeding habits

Summary Eight insects (some adult and some larval forms) are studied for the presence of sialic acids in the cells of the salivary glands. This was sought by staining with alcian blue and Azure A at different pH accompanied by acid hydrolysis, sialidase digestion and methylation-saponification.On the basis of susceptibility to acid hydrolysis and sialidase digestion, different sialic acids are discernable. Though there is apparently no correlation between the secretion of sialic acid and the feeding habits of these insects, there is an interesting correlation between these two in the case of nectar and pollen eating habit of Apis.Presented at the 56th Session of Indian Science Congress. 2–9 January, 1969, Bombay, India.     

Fluid intake rates in ants correlate with their feeding habits

This study investigates the techniques of nectar feeding in 11 different ant species, and quantitatively compares fluid intake rates over a wide range of nectar concentrations in four species that largely differ in their feeding habits. Ants were observed to employ two different techniques for liquid food intake, in which the glossa works either as a passive duct-like structure (sucking), or as an up- and downwards moving shovel (licking). The technique employed for collecting fluids at ad libitum food sources was observed to be species-specific and to correlate with the presence or absence of a well-developed crop in the species under scrutiny. Workers of ponerine ants licked fluid food during foraging and transported it as a droplet between their mandibles, whereas workers of species belonging to phylogenetically more advanced subfamilies, with a crop capable of storing liquids, sucked the fluid food, such as formicine ants of the genus Camponotus. In order to evaluate the performance of fluid collection during foraging, intake rates for sucrose solutions of different concentrations were measured in four ant species that differ in their foraging ecology. Scaling functions between fluid intake rates and ant size were first established for the polymorphic species, so as to compare ants of different size across species. Results showed that fluid intake rate depended, as expected and previously reported in the literature, on sugar concentration and the associated fluid viscosity. It also depended on both the species-specific feeding technique and the extent of specialization on foraging on liquid food. For similarly-sized ants, workers of two nectar-feeding ant species, Camponotus rufipes (Formicinae) and Pachycondyla villosa (Ponerinae), collected fluids with the highest intake rates, while workers of the leaf-cutting ant Atta sexdens (Myrmicinae) and a predatory ant from the Rhytidoponera impressa-complex (Ponerinae) did so with the lowest rate. Calculating the energy intake rates in mg sucrose per unit time, licking was shown to be a more advantageous technique at higher sugar concentrations than sucking, whereas sucking provided a higher energy intake rate at lower sugar concentrations.