Ecology of Inland Waters and Estuaries

1. 1. The occurrence, metabolism and physiological significance of non-protein nitrogenous compounds in fish are discussed. 2. 2. Free histidine and imidazole dipeptides serve as biological buffers, besides functioning in transport mechanisms for copper and zinc. 3. 3. Trimethylamine oxide is a detoxification product of dietary trimethylamine. It participates in osmoregulation of marine species and it stabilizes elasmobranch protein structure in the presence of large amounts of urea. The latter two functions are shared with other methylamine compounds (sarcosine, betaine). 4. 4. When present in high concentrations, taurine participates as an osmolyte in cell volume regulation. Teleosts condensate bile acids with taurine for the synthesis of bile salts. The general function of taurine is still unclear. 5. 5. Besides their recognized role as precursors for the biosynthesis of amino acids, purines and pyrimidines, amides participate in a mechanism for the control of ammonia levels and ammonia excretion rates. Glutamine synthesis protects the brain against the consequences of an ammonia load. 6. 6. Branched-chain amino acids are important substrates for energy metabolism in the telecost myotome. The metabolic fate of their amino group requires further investigation. 7. 7. During environmental anoxia, Cyprinids use both carbohydrates and amino acids as substrates for anaerobic energy production. Possible biochemical mechanisms are discussed. A theoretical analysis shows that the carbon skeleton of certain amino acids may appear as ethanol, whereas that of others can be incorporated into storage lipids. The nature and energy yield of the pathways involved have not yet been clarified.

Biochemistry of non-protein nitrogenous compounds in fish including the use of amino acids for anaerobic energy production

The physico-chemical properties of the Ogun River were recorded between January 1974 and December 1975. A wet season with mean monthly rainfall of 9.72 cm. (s.d. = 5.07 cm) occurred from April through October, while a dry season with mean monthly rainfall of 0.56 cm. (s.d. = 0.99 cm) occurred between November and March. The seasonal changes in the rainfall of the drainage area resulted in an alternation of the hydrological regimes of the river. The high water level of the river that arose as a result of the rains made the water flowed unidirectionally from July through December. After the rains, the water level receded gradually to a point where by January the river broke up into a chain of pools. In a lotic state, the water's tansparency, pH, total alkalinity and conductivity were lower, while its dissolved oxygen, free carbon dioxide concentrations were higher than the corresponding conditions in the residual pools formed when the water was lentic. In this latter form, the observed diurnal surface water temperature fluctuations were more and diel thermal stratification occurred. It was evident that the water in both phases was well aerated. The diurnal fluctuations in the water temperatures and the relationships between the determined environmental factors were assayed.

The physico-chemical hydrology of a tropical seasonal river-upper Ogun river

This chapter describes the biochemical events involved in the transition from a resting to an actively swimming condition. The chapter deals with metabolism in myotomal muscle, but there are other organs, integrally important for the maintenance of homeostasis, that may be extremely expensive to operate during sustained swimming. For instance, the cost of osmoregulation, in freshwater, for actively swimming rainbow trout ( Salmo gairdneri ), may be as high as 30% of the total metabolism of the fish. Much of this energy expenditure must be borne by the gills. The cost of maintaining the cardiac pump may also be quite substantial. In fact, at high oxygen consumption rates, this may approach 15% of the total metabolism of the animal. Thus, the myotomal muscle per se may account for only about 50% of the total energy output. In light of this, it is somewhat surprising that tissues other than skeletal muscle are rarely studied by fish physiologists interested in metabolic alterations during swimming. The chapter describes the control of metabolism in these support tissues and skeletal muscle; however, the understanding of metabolism in fish tissues is at best fragmentary. Hence, where appropriate, the better-studied mammalian systems are called upon to complement and supplement the discussion.

8 - Metabolism in Fish During Exercise

. The fry of four species of planktivorous carp, silver carp, Hypophthalmichthys molitrix (Valenciennes), bighead carp, Aristichthys nobilis (Richardson), rohu, Labeo rohita (Hamilton), and catla, Catla catla (Hamilton), were grown in monoculture in ponds in Mymensingh, Bangladesh in order to determine electivity and the extent of dietary overlap. Other than an avoidance for Cyanobacteria, electivity was found to be low in most instances, although the low productivity of the ponds may have had some influence. Dietary overlap was greatest between catla and silver carp (0–52) and between catla and bighead carp (0–48).

Food selection, electivity and dietary overlap among planktivorous Chinese and Indian major carp fry and fingerlings grown in extensively managed, rain‐fed ponds in Bangladesh

Selectivity of food byLabeo rohita (Ham.) was studied in a stocking pond (Moat), by calculating an Electivity index (E) for each food organism as described byIvlev (1961). It was found thatL. rohita was definitely selective in its feeding. In case of fingerlings, there was a strong selection for zooplanktonic organisms (Arcella andDifflugia among protozoans,Keratella andBrachionus among rotifer andDaphnia andCyclops among crustaceans) and smaller algae (Cosmarium andClosterium among desmisd,Euglena andVolvox among phytoflagellates and algal spores and zygotes) while most of the phytoplanktonic organisms, belonging to green algae, diatoms and blue green algae, were avoided. In case of adults, a strong negative selection was observed for all zooplanktonic organisms and a strong positive selection for most of the green algae and diatoms (Ankistrodesmus, Zygnema, Spirogyra, Selenastrum, Pediastrum, Scenedesmus, Tetraspora, Stephanodiscus, Naviculla, Diatoma, Synedra andNitzchia). However, all blue green algae were avoided.

Food selection by Labeo Rohita (Ham.) and its feeding relationship with other major carps

Diurnal variations in water chemistry and plankton in this eutrophic tropical freshwater ponds were quite apparent. Large fluctuations were noted in dissolved oxygen, pH, carbonate and bicarbonate concentrations. The pond water gets oversaturated with oxygen during day (24.2 p.p.m.) and depleted in the night (1.2 p.p.m.). Diurnal migrations of plankton were not in conformity with temperate waters.

Diurnal variations in a shallow tropical freshwater fish pond in Shahjahanpur, U.P. (India)

Seasonal changes in physical, chemical and biological characteristics in a perennial fish pond were investigated. A uniform distribution of temperature at all the depths was recorded. Wide seasonal fluctuations were noted in transparency and turbidity. The transparency was found to be- affected by turbidity and phytoplankton crop. The Pond Moat was gerierally found saturated with oxygen throughout the year excepting in August, 19(58. Clinograde type of oxygen distribution was noted at different water levels. Fluctuations in the carbonate alkalinity alongwith pH values were mainly due to photosynthetit activity of phytoplankton and other higher aquatic plants

Seasonal chanoes in the limnology of a perennial fish pond at aligarh

Mixed phytoplankton, zooplankton and Thermocyclops hyalinus collected from Fort Moat, at Aligarh (U.P.) India, were analysed for water, nitrogen and phosphorus. Results are generally in agreement with observations of earlier investigators.

Water, nitrogen and phosphorus in freshwater Plankton

Seasonal fluctuations in gross and net primary production values were quite apparent in surface waters and showed a bimodal type of distribution. The values were generally high during post winter months (March to May) and low during winter (February) and monsoon months (July and August). At different depths the rate of primary production was always found decreasing from surface to bottom. The rate of photosynthesis was found to be highly variable from time to time and at different depths.

A. Qayyum Siddiqui

Papers

Food selection by Labeo Rohita (Ham.) and its feeding relationship with other major carps

Diurnal variations in a shallow tropical freshwater fish pond in Shahjahanpur, U.P. (India)

Seasonal chanoes in the limnology of a perennial fish pond at aligarh

Water, nitrogen and phosphorus in freshwater Plankton

Primary production in a tropical fish pond at Aligarh, India