Metabolic enzyme activities in larvae of the African catfish, Clarias gariepinus: changes in relation to age and nutrition

Abstract

The influence of ontogeny and nutrition on metabolic enzyme activities in larvae of the African catfish, Clarias gariepinus, was studied. After start of exogenous feeding, the larvae were reared for 10 days under three different nutritional conditions: Artemia nauplii, a dry starter diet, and starvation. The live feed gave the best growth (96 mg within 10 days) whereas the dry diet resulted in low growth (33 mg). This growth difference was reflected in larval RNA and DNA concentrations, but not in the levels of soluble protein. Enzymes representing the following aspects of metabolism have been analysed: NADPH generation (G6PDH, ME), glycolysis (PFK, PK), gluconeogenesis (FDPase), amino acid catabolism (GOT, GPT) and oxidative catabolism (CS). All enzymes were present from the start of exogenous feeding onwards, but their maximum specific activities displayed different developmental patterns. In catfish larvae fed on Artemia, G6PDH and ME activities steadily increased with age and weight of the larvae. CS levels remained, after an immediate enhancement upon onset of exogenous feeding, on a rather stable plateau. The amino acid-degrading enzymes GOT and GPT showed maximum levels at days 3-5 of feeding or at a body weight of 10-20 mg, but decreased thereafter. Activities of PFK, PK and FDPase showed low initial levels, and increased significantly with age and size. Based on the ontogenetic patterns of metabolic enzymes, in C. gariepinus larvae an early and a late developmental phase can be distinguished. During the early phase, the glycolytic and gluconeogenetic capacities are low, whereas they are enforced during the later phase. The oxidative capacity is high both during the early and the late phase. The metabolic changes in catfish development coincide with other major ontogenetic events, e.g., alterations of muscle organization, gill morphology, respiration and stomach structure and function. Rearing catfish larvae on a dry diet instead of Artemia partly altered the developmental pattern described: The ontogenetic elevation of CS, PFK and FDPase was delayed and the early peak in GOT and GPT activities was not realized. Particularly during the early developmental phase, the enzyme behaviour of the larvae fed on dry food was similar to that of starved larvae.

Effects of lead nitrate on the activity of metabolic enzymes during early developmental stages of the African catfish, Clarias gariepinus (Burchell, 1822)

“…Only ontogenetic variations during development after the start of exogenous feeding have been studied (Somero and Childress 1985;Clarke et al 1992;Segner and Verreth 1995). In the present work, the enzymatic activities of G6PDH, LDH and PK exhibited variability during the early embryonic stages of C. gariepinus (30 h-PFS-168 h-PFS), a period that included pre-hatching and post-hatching intervals.…”

“…Homogenisation of the whole animal is a reliable method that provides a reasonable index of total enzyme activity in individuals whose body mass is predominantly composed of muscle tissue (Berges and Ballantyne 1991;Lemos et al 2003). This procedure makes interpretation of the results more equivocal than investigations on older life stages when specific organ preparations can be used (Segner and Verreth 1995).…”

“…This means the utilisation, still, of maternal enzyme mRNA for a long period, in comparison with C. idellus (Mekkawy and Lashein 2003) and other fish species in which maternal proteins are synthesised up to the blastula stages, or even to gastrulation. Increase of G6PDH and LDH activities from 96 h-PFS (2 days after hatching) onwards, before the onset of exogenous feeding (at 196 h-PFS of C. gariepinus), referred to the early substantial capacity for NADPH generation based on switchon zygotic gene mechanisms (Segner and Verreth 1995). Segner and Verreth (1995) referred to such a capacity existing from the onset of exogenous feeding onwards, as evidenced by the increase of G6PDH activity with age.…”

“…Increase of G6PDH and LDH activities from 96 h-PFS (2 days after hatching) onwards, before the onset of exogenous feeding (at 196 h-PFS of C. gariepinus), referred to the early substantial capacity for NADPH generation based on switchon zygotic gene mechanisms (Segner and Verreth 1995). Segner and Verreth (1995) referred to such a capacity existing from the onset of exogenous feeding onwards, as evidenced by the increase of G6PDH activity with age. Many authors referred to the increase of LDH and G6PDH enzyme activities with increasing larval age of different fish species (Pelletier et al 1995;Nathanailides 1996).…”

Metabolic adaptation of MDCK cells to different growth conditions: Effects on catalytic activities of central metabolic enzymes

“…It is evident from several studies on metabolism of animal cells that changes in enzyme activities highlight metabolic changes (Fitzpatrick et al, 1993;Leveille and Hanson, 1966;Neermann and Wagner, 1996;Segner and Verreth, 1995;Vriezen and van Dijken, 1998;Yallop et al, 2003). It is, however, worth mentioning that although change in enzyme activity is mostly represented by change in the total amount of an enzyme, catalytic activity can also be altered by allosteric effectors that, for instance, change the substrate affinity (K m ) of the enzyme.…”