Ioannis T. Karapanagiotidis

Effects of Different Diets on the Digestive Physiology of Adult Norway Lobster Nephrops norvegicus

ABSTRACT Rearing Norway lobsters for restocking is a management option to compensate fishing overexploitation, but this requires, among other topics, developing specific pellet diets. The activity of digestive enzymes and the histological organization of the hepatopancreas were analyzed to assess the effectiveness of a pellet diet on digestive performance. Thirty animals were reared individually for 6 mo, fed with mussels and pellets or starved. Comparisons with wild lobsters were also conducted. Survival rate of lobsters fed with frozen mussels was the greatest. Trypsin and amylase activity in the hepatopancreas of the lobsters fed pellets was greater than that of other treatments. In contrast, pepsin activity in the gastric juice of starved animals was the greatest. Levels of alkaline proteases in the gastric fluid were greater in lobsters fed with mussels and the pellet diet in contrast to fasted animals. Amylase was greater in specimens fed frozen mussels. The greatest level of lipid accumulation observed in lobsters fed with the pellet diet indicated a physiological imbalance between the absorptive and transport capacity of the hepatopancreatic cells resulting from an excess of dietary lipids. These results might serve as a reference for future studies for formulating feeds specifically designed for Nephrops norvegicus.

A novel image processing method to determine the nutritional condition of lobsters

The digestive gland of crustacean is involved in various metabolic activities, including the synthesis and secretion of digestive enzymes that begin the process of food digestion, intracellular digestion and absorption of nutrients, storage of reserves, and disposal of waste products. It consists of two glandular lobes which extensively subdivide to form a complex of blind-ending tubules, whose size, surface area, and digestive cells are associated with intracellular digestion and the nutritional status of the organism. The aim of this paper was to study the morphology of the digestive gland in various lobster species and calculate the surface area of tubules, lumen and digestive cells (R-, F-, and B-cells) and their ratios to total tubule surface area. The similarity in ratios obtained in this study between individual lobsters suggests that the method developed in this study can be successfully applied to a range of species. This study describes a novel image processing algorithm for the automatic measurement of the hepatopancreas structure using stained cross sections of digestive gland tubules. The proposed new methodology could be used for studying the physiology and nutrient metabolism of lobsters and other crustaceans. The computer-aided analysis described in this paper is accurate for the quantitative assessment of the lobsters digestive gland structure.

Measurement of the feed consumption of Nephrops norvegicus feeding on different diets and its effect on body nutrient composition and digestive gland histology

The feed consumption of Nephrops norvegicus (Linnaeus, 1758) reared in captivity and fed either mussel or a pelleted diet was measured for ten weeks. Both groups of lobsters showed a similar feed consumption, which averaged 54.7 and 49.9 mg of dry weight day−1 lobster−1, respectively. Tail muscle and digestive gland nutrient composition was unaffected by the different type of diet, except muscle lipid contents. The pelleted diet resulted in increased moults, but the mussel diet was more effective with reference to survival. A similar digestive condition was also evidenced between the groups despite the bigger B-cells area in the digestive gland tubules of the pellet-fed lobsters. These findings contribute to a better understanding of the nutrition and feeding capabilities of N. norvegicus reared in captivity, which is critical for the development of suitable diets for its potential in aquaculture.

Morphological study of muscular tissue collagen of wild and reared Cornu aspersum (Müller, 1774)

Muscular tissue collagen fibrils’ diameter and period of reared and wild snails (Cornu aspersum) were measured in order to investigate the role of nutrition on the collagen. Wild adult individuals were collected from Crete (Greece) and compared with adult individual snails reared under laboratory conditions fed a formulated diet. Transmission electron microscope and image analysis algorithms were used in the study. Statistically significant differences between the diameters of the collagen fibrils in the reared and the wild snails were found, and the D-period of the fibrils differed.