Ecophysiological studies on the developing eggs and embryos of the European lobster Homarus gammarus

During the course of its embryonic development, the European lobster Homarus gammarusLinnaeus exhibits progressive increases in content of water (54.0 to 83.1%), ash (2.7 to 16.7%), protein (47.4 to 50.9%) and non-protein nitrogen (1.0 to 2.4%), and steady decreases in content of fat (43.8 to 25.4%) and energy (6343 to 5431 cal/g dry organic substance). Cumulative yolk utilization efficiency during the total development is 81.8% for dry weight; the corresponding value for energy is 60.1, for protein 75.6 and for fat 47.4%. Energy content of a single egg is 10.49 cal. Of 4.20 cal expended for metabolic processes of the embryo, only 13.3% energy is drawn from protein oxidation; fat oxidation supplies as much as 87.7% energy, that of carbohydrate only 2.3%. Embryonic development results in a remarkable decrease in net yolk utilization efficiency, which falls from 85.5% in the early developmental stages, to less than 70% in later developmental stages. The mean dry weight of a single egg membrane increases from 38 μg (2.2% of egg weight) in a freshly laid and attached egg, to 81 μg in an egg with an almost completely developed embryo. This result supports the earlier observation of Cheung (1966) that the formation of the inner chitinous egg membrane occurs after the egg is laid and attached to the setum. Protein seems to be the major constituent of the egg membrane (4049 cal/g dry weight), which has the following composition: protein 70.4%, non-protein nitrogen 0.13%, ash 2.83%. Initial permeability of the egg membrane to water (about 6% of the total water requirement is let in) is followed by a period during which the egg membrane is almost impermeable to water (stages I to III); the egg membrane becomes permeable to water again and lets in 85% of the total water requirement (the rest, i.e. 9%, is metabolic water) at a relatively advanced stage of development. These assumed changes in egg membrane permeability appear to be indicative of variations in the egg's osmoconcentration leading to shiftings in net transport of water. Rates of water and salt uptake during embryonic development are essentially parallel (Fig. 1). The egg membrane remains permeable to salts throughout development; salt intake almost doubles after the egg passes through stage III. A single egg, weighing 3.7 mg requires 4.9 mg water for successful completion of embryonic development. The imbibition of water by the developing marine demersal egg seems to (1) serve in osmotic hatching; (2) float the hatched larva by means of specific gravity reduction; (3) aid the larva to quickly adjust its body temperature. The simple osmotic hatching mechanism, proposed by previous workers, seems to be inadequate to account for the events and timing of the hatching process in the lobster. It is suggested that hatching time is determined not solely by increased internal pressure caused by inflow of water and salts, but also by some unknown internal factor. In the lobster egg, as well as in many other marine demersal eggs, protein metabolism is suppressed to a considerable extent, and fat metabolism is “geared up” Thus, the non-cleidoic lobster eggs exhibit metablic properties which are typical of cleidoic eggs. This finding is discussed in the light of Needham's (1950) concept of “cleidoicterrestrial and non cleidoic-aquatic eggs”

Yolk utilization in the gastropod Crepidula fornicata

The increases in constituents per unit weight of eggs during embryonic development of the gastropod Crepidula fornicata amounted to 14.6% for ash, 1.0% for protein, and 0.3% for non-protein nitrogen. During the same stages, fat content decreased from 33.7 to 20.3%, carbohydrate from 10.2 to 7.7% and energy content from 6209 to 5298 cal/g dry organic substance. The cumulative efficiencies for yolk utilization were 83.8% for dry weight, 61.0% for energy, 85.1% for protein, 50.7% for fat, and 63.6% for carbohydrate. A single egg contained 0.0269 cal, a single veliger 0.0164 cal. Of the 0.0105 cal expended on metabolic processes of the embryo, oxidation of fat contributed as much as 65.3%, while that of protein and carbohydrate amounted only to 18.8 and 6.3%, respectively. On the basis of ecophysiological considerations, a new classification of eggs is proposed

Intake and coversion of food in the fish Limanda limanda exposed to different temperatures

In the flat fish Limanda limanda L., feeding rate and conversion efficiency were studied as functions of body weight, sex, temperature and food quality. When offered herring meat at 13 °C (series I), females (live weights 1 to 150 g) consume more food than males; the magnitude of this difference is body weight-dependent. With increasing wieght, both females and males consume less food per unit body weight per day. Variations in daily ration are considerable; the range of deviation from mean feeding rate is about 60% for males and 40% for females. The range of deviation does not vary significantly among females and males of different body weights. At the same temperature level (13 °C; series II), females consume almost the same, or even less, cod meat than males. Among individuals of series I and II, there is a little difference in the feeding rate; however, herring-fed individuals obtain about 2 times more energy than cod-fed individuals. Each gram wet weight of herring meat yields 2001, each gram cod meat 1137, calories. Small individuals completely cease to feed at 3°C; they feed little at 8 °C. Larger females consume maximum amounts at 8 °C. Small individuals consume maximum amounts at higher temperatures. Thus, with increasing body weight (age), the temperature for maximum feeding shifts downwards. Feeding with cod or herring meat results in considerable changes in composition and calorific content of L. Limanda. The magnitude of these changes depends both on temperature and food quality. Food conversion efficiency values of herring-fed individuals are about 1 1/2 times higher than of cod-fed individuals. In series I and II, females are more efficient converters than males. In individuals weighing more than 50 g, conversion efficiency decreases in the order: 8°, 13°, 18° C; in smaller individuals this order is 13°, 18°, 8 °C. Conversion rate is about 2 to 5 times faster in individuals fed herring meat than those receiving cod meat. Conversion rate decreases in the order 13°, 8°, 18 °C in males, and in the order 18°, 13°, 8 °C in females; females of more than 80 g are exceptional in that they reach the maximum at 8 °C. From the data on food intake and food conversion, the biologically useful energy available for metabolism has been calculated for each test individual kept at 13° and 18 °C. At these temperature levels, the weight exponents are about 0.6; the ‘a’ value or metabolic level for the 18 °C series is about 2 times higher than that at 13 °C. Thus, temperature affects metabolic rate but not the exponential value. The exponential value for the body weight-metabolism relation at 13 °C is for dab fed herring meat 0.9; the ‘a’ value amounts to about half that for dab fed cod meat. Food quality, unlike temperature, alters not only the exponential value but also metabolic rate

Guidelines for research and utilization of genetically modified fish

Asian scientists are the first to initiate research in transgenic fish and Asia is the centre of research activity in transgenic fish. Transgenic fish thus far generated display desirable traits, excepting a few, in which reproductive performance seems to have been impaired. Only 12 countries have framed their respective national policy or regulations on genetically modified aquatic organisms. However, transgenic research is growing so fast that these guidelines and regulations will have to be revised from time to time. GH-transgenes are analogous to selected and/or domesticated lines, capable of growing 4-5 times faster. Transgenics, that are anti-freeze protein transformants, may not interfere as much as exotic fish. Regarding biological containment, available methods for inducing sterility of transgenics are briefly described

Effects of feeding and starvation on growth and swimming activity in an obligatory air-breathing fish

There exists an enormous body of literature on metabolism of fishes as studied by oxygen consumption. Since standard metabolism relates to 'maintenance energy cost' of nonfeeding, nondigesting, nongrowing, nonactive fish, Winberg (1956) rightly appealed for more studies on active metabolism. Studies on -active metabolism required exercising apparatus and techniques, such as grids or electrified fields, to ensure a high sustained level of activit

Erythrocyte count and haemoglobin concentration of some tropical fishes

In all three species studied, values obtained for blood properties such as erythrocyte counts haemoglobin concentration were the highest for males, intermediate for females and least for juveniles. The reason for the sex-dependent changes in the blood properties is not at present clear

Norethindrone ensures masculinization, normal growth and secondary sexual characteristics in the fighting fish, Betta splendens

To ensure masculinization and normal growth of the obligately air-breathing fighting fish Betta splendens, norethindrone acetate (NE) was administered through discrete immersions for 3 h each on the second, fifth and eighth day post-hatching (dph) at selected concentrations (250, 500, 750, 1000 and 1250 μg/l). Immersions at 1000 μg/l ensured the maximum of 92% masculinization, 71% survival, normal growth and appearance of secondary sexual characteristics. NE reduced the air-breathing frequency on the fifth and eigth dph. It also reduced the frequency in males depurated for 172 days following the treatment, although males treated at 750 μg/l almost restored the frequency. In the ovary of the treated but persisting females, it reduced the number of vitellogenic oocytes and increased the vacuolar area. In the testis of the treated males, it reduced the number of spermatogonia and increased the vacuolar area. The treated males could neither induce the female to spawn as many eggs nor accommodate as many fertilized eggs within the bubble nest, as that of the control. While the control females attained puberty on the 140th dph and spawned 122 eggs once every 16 days, the persisting females, which were previously treated at 1000 μg/l, postponed puberty to the 183rd dph and prolonged the inter-spawning period to 40 days. During the 240-day experiment, NE reduced the cumulative progeny production from 764 to 104 (13.6% of the control)

Surfacing activity and food utllization in a tropical air-breathing fish exposed to different temperatures

In tropical countries like India, \vhere availability of freshwater is limited , air-breathing fishes may be chosen for aquaculture, as they thrive in shallow waters deficient in oxygen. However, the advantageous air-breathing habit of these fishes and the consequent need to surface more or less at regular intervals may impose a considerable drain of energy, which otherwise could have been channelled into fish productio

Food utilization in the fish Channa striatus exposed to sublethal concentrations of DDT and methyl parathion

Sublethal concentrations of DDT and methyl parathion (MP) in the medium significantly affected the rates of feeding, absorption and conversion in Channa striatus. Fish exposed to 250 ppb DDT or MP consumed 23 or 50% less food than those exposed to pesticide-free water. Correspondingly, absorption rate also decreased from 120 cal/g live fish/day in the control to 88 and 59 cal/g/day in those exposed to 250 ppb DDT and MP. Efficiency to convert the absorbed food into body substance dropped from 30% in the control to 6 and 12% in the 250 ppb DDT and MP groups. Metabolic rate of the control averaged to 84 cal/g/day; whereas exposure to DDT did not significantly affect the metabolic rate, a concentration of 250 ppb MP depressed the rate to 52 cal/g/day

Androgenesis and conservation of fishes

Due to non-visibility of egg nucleus, the established scheme of nuclear manipulation to clone fish may prove a difficult task. However, fishes are amenable for interspecific androgenetic cloning. A recent discovery of using cadaveric sperm to successfully generate progenies has opened the possibility of adopting a simple, widely practicable method of post-mortem preserved (at - 20°C) sperm to induce androgenesis. Inactivation of maternal genome by UV-irradiation and activation of genome-inactivated homologous or heterologous egg by a single diploid or two haploid fresh or preserved sperms are some landmark events, which have not only accelerated research activity but also focused on the importance of androgenesis in aquaculture and conservation of fish germplasm. With the absence of acrosome in the teleostean sperm, fertilization in fish is not a species-specific event. Eggs of many teleosts are amenable for heterospecific insemination. Successful heterospecific insemination results in activation or fertilization of an ovum of an alien species and is the most important strategic step for induction of interspecific androgenetic cloning. Polyspermy, especially dispermy occurs in nature and can be experimentally achieved after incubation of the milt in calcium chloride or polyethylene glycol. The paternal origin of androgenotes is verified using selected phenotypic, protein and/or molecular markers as well as karyotyping and progeny testing. Recently, reporter genes, the green fluorescent protein gene and the Tc1 transposan-specific marker have also been used. While confirming the paternity of androgenotes, progeny testing has also indicated the unexpected occurrence of females, which are, however, shown to carry XY using a single diploid, rather than two haploid sperms for activation. About 84% androgenotes succumb during embryonic development. Haploid genome regulates the time scale of developmental sequence in both homologous and heterologous eggs of Puntius spp., as effectively as that of diploid. A couple of research groups have restored a fish species using its preserved sperm and genome-inactivated eggs of another species. A comparison on the source, technique and genomes used for generation of clones of mammals and androgenetic clones of fishes indicates that from the point of conservation and aquaculture, interspecific androgenetic cloning in fishes has an edge over that of mammals