1. While the balance of light and nutrients is known to influence the food quality of herbivores by altering algal phosphorus and nitrogen content, the combined effects of light and nutrients on fatty acid synthesis in freshwater periphyton are relatively unknown. In this study, we manipulatedlightandphosphorusconcentration inlarge,flow-throughexperimentalstreams to examine their effects on both elemental stoichiometry and fatty acid content in periphyton. 2. Two levels of phosphorus (4 and 80 lg L )1 ) and three of light (17, 40, 110 lmol photons m )2 s )1 ) were applied in a factorial design in two separate experiments. Diatoms dominated periphyton communities in both experiments, comprising >95% of algal biovolume. Periphyton growth in the streams was simultaneously affected by both resources, even at low rates of supply. 3. Periphyton C ⁄ P and C ⁄ N ratios increased with light augmentation and decreased with phosphorus enrichment, and consistent with the light : nutrient hypothesis (LNH). Light effects were strongest in streams with low phosphorus concentrations. 4. Periphyton fatty acids reflected the dominance of diatoms : palmitic (16 : 0), palmitoleic (16 : 1x7) and eicosapentanoic (20 : 5x3) were the principal saturated (SAFA), monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA), respectively. Linoleic (18 : 2x6) and linolenic (18 : 3x3) acids, characteristic of chlorophytes and cyanophytes, were rare, comprising <2% of total fatty acids. 5. Periphyton fatty acid profiles were highly sensitive to light and phosphorus. The proportion of fatty acids comprised by SAFA and MUFA increased with light augmentation and decreased with phosphorus enrichment, whereas PUFA decreased with light and increased with phosphorus. Light effects on fatty acid composition were strongest in phosphorus-poor streams. PUFA declined with increasing light ⁄ phosphorus ratios in the streams, whereas 'energy' fatty acids (16 : 0 and 16 : 1) increased. The ratio of SAFA ⁄ PUFA was strongly and positively correlated with C ⁄ P and C ⁄ N ratios. SAFA and MUFA, normalised to dry mass, increased two-to threefold with increasing light, while PUFA normalised to dry mass was not significantly affected by light. 6. Similarities in the responses of fatty acids and elemental stoichiometry to light and phosphorus treatments suggested that they were influenced by a common mechanism. Both components of food quality appeared to be sensitive to light-regulated rates of carbon fixation which, when coupled with insufficient supplies of phosphorus, caused diatom cells to store surplus carbon in SAFA, MUFA and other carbon-rich compounds that diluted both essential fatty acids and mineral nutrients.

To clarify the dynamics and regulation of oogenesis in single-and multiple-spawning cyprinid fish with group-synchronous oocyte development, a multidisciplinary approach to their reproduction was undertaken using three species from the River Meuse (Belgium): the roach Rutilus rutilus as a single spawner, and the bleak Alburnus alburnus and the white bream Blicca bjoerkna as multiple spawners. The gonadosomatic index (GSI) and histomorphometric changes (distribution of oocyte size, relative proportion of the various oocyte stages) in the ovary are compared. Different patterns of GSI and oocyte growth were observed both between the single-and multiple-spawner fish and between the two multiple spawners. Maximum GSIs were higher in roach (21%) than in bleak and white bream (17·7 and 14·5%, respectively), and compared to the rapid decline of GSI in the roach population, the GSI of multiple spawners decreased progressively during the spawning season. In roach, a short gonadal quiescent period and an early onset of vitellogenesis was recorded from late summer onwards whereas, in bleak and white bream, exogenous vitellogenesis was not systematically observed before winter. A protracted spawning season and/or a low water temperature in autumn are hypothesized to explain this long period of gonadal quiescence. In bleak, during the spawning season, the oocytes recruited arose from the stock of endogenous vitellogenesis and attained the final maturation stage very rapidly. This recruitment occurred during the whole spawning season. In white bream, the differentiation of vitellogenic oocytes from smaller oocytes was completed before the onset of the spawning season. During the spawning period, the proportion of vitellogenic oocytes decreased progressively whereas the percentage of oocytes in the final maturation stage remained approximately constant. 1996 The Fisheries Society of the British Isles

In vitro studies of brush-border intestinal transport of dipeptides and cytoplasmic hydrolysis in fish suggest that these processes could be key mechanisms in the absorption and utilization of nutrients for growth. However, in vivo experimentation to study the nutritional importance of these processes was needed. We compared three dietary formulations based on free, peptide and protein sources of amino acids. Our results were the first to show that a synthetic dipeptide (PP)-based diet could support growth in the early stages of ontogenesis of a teleost fish, rainbow trout (Oncorhynchus mykiss), whereas a free amino acid (FAA)-based diet failed. We found that fish fed an FAA-based diet had an increased rate of ammonia excretion [1.78 +/- 0.19 mmol NH(3)-N/(kg body wt.h)], compared with fish fed a PP-based diet [1.25 +/- 0.07 mmol NH(3)-N/(kg body wt.h)], suggesting that deamination is involved in the metabolism of dietary FAA. Teleost fish are known to obtain a high proportion of total energy from protein, compared with higher vertebrates. However, we found that feeding trout alevins a PP-based diet increased postprandial oxygen consumption for 2 to 24 h, whereas other treatments decreased 24-h postprandial metabolism. This may indicate that peptide metabolism is less efficient than protein metabolism. Juvenile rainbow trout differed from alevins in their response to FAA- and PP-based diets. These observations strongly suggest that intestinal dietary peptide transport and hydrolysis could support protein synthesis and growth in vertebrates that respond poorly to FAA-based diets. We conclude that nutrient administration may be improved by manipulating dietary peptide composition and peptide/protein ratios, leading to better utilization of synthetic peptides, with nutritional and therapeutic implications for all vertebrates.

Accurate diet estimation has long been a challenging issue for researchers investigating predators because of constraints associated with stomach content analyses. Fatty acid signature analysis offers an alternative avenue to study long-term diet trends in consumers. Despite the wealth of experiments involving fatty acids of fish and their diets, few have evaluated quantitative fatty acid signature analysis (QFASA) with fish consumers. To this end, we fed juvenile lake trout (Salvelinus namaycush), round goby (Neogobius melanostomus), and yellow perch (Perca flavescens) various invertebrate species and back-classified each predator to its respective prey using only fatty acids. Estimates were highly accurate when metabolism of diets was natively accounted for by using fatty acid profiles of predators fed known diets as the “prey library”. While highly accurate results were obtained, accounting for each predator–prey relationship limits the use of QFASA to predators that consume a limited number of species. We call for specific knowledge as to how fatty acid profiles reflect each predator–prey interaction before attempting to use fatty acids to quantify a consumer’s diet. Only after incorporating such data will QFASA provide an accurate view of individual’s diets when stomach content data are not available or are invalid.

No abstract

Annual changes in plasma of estradiol-17 beta, testosterone, and 17,20 beta-dihydroxy-4-pregnen-3-one concentrations were measured, by radioimmunoassay, in female gudgeon Gobio gobio a fish which has an asynchronous-type ovary containing oocytes at various stages of development and spawns several times during the reproductive period. The gonadosomatic index and the relation between stages of maturity and steroid concentrations were also followed during the reproductive cycle. Plasma levels of estradiol-17 beta, testosterone, and 17,20 beta-dihydroxy-4-pregnen-3-one were low from October to April and increased rapidly in May to reach 0.61 +/- 0.31; 2.3 +/- 0.42; and 3.17 +/- 0.68 ng/ml, respectively. Elevated levels were maintained during spawning when vitellogenic oocytes are present alongside oocytes in final maturation. Histological analysis of the ovary indicated that an important number of spawnings has occurred since the proportion of oocytes in final maturation stage was very low (less than 1%). Fish in the regressive phase also presented high steroid levels. The vitellogenic oocytes in preovulatory atresia and the postovulatory follicles may be responsible for these events.

No abstract

The purpose of this study was to determine the effects of perchlorate on thyroid function in mosquitofish. Adult mosquitofish were exposed to 0, 0.1, 1, 10, 100, and 1000 mg/L sodium perchlorate for 2, 10, and 30 d. Whole body thyroxin (T4) content and histological assessment of thyroid follicles (e.g., follicular epithelial height, hyperplasia, hypertrophy, and colloid depletion) were used to gauge alterations in thyroid function. Follicular epithelial cell height, hyperplasia, and hypertrophy increased with increasing perchlorate concentration, especially in fish exposed for 30 d, and these effects were statistically significantly different from control at concentrations as low as 0.1 mg/L (nominal concentration). The percent occurrence of follicles with depleted colloid decreased with increasing perchlorate concentration, which is contrary to what is expected with thyroid inhibition. There also was a decrease in whole body T4 concentration in fish exposed to perchlorate for 30 d, but clear dose-response relationships were less evident for whole body T4 than for histopathological endpoints. In conclusion, thyroid histopathology provides a sensitive biomarker for thyroid endocrine disruption at environmentally relevant concentrations of sodium perchlorate, and whole body T4 is a less sensitive indicator of perchlorate exposure than is histopathology.