We examined the effect of the double restriction-recovery cycle on survival, growth, and nutritional status of the freshwater prawn Macrobrachium borellii (Nobili, 1896), native to floodplain rivers of Argentina. The restriction period consisted of intermittent starvation (alternating four-day feeding with no feeding for four days) and a recovery period of continuous feeding following the restriction period. Survival was high over a 20-week trial with cycles of food scarcity. Prawns showed a slight impact on their growth throughout the entire first cycle of restriction-recovery; however, compensatory growth was not triggered. The reduction of growth was markedly more drastic after the second restriction period, but compensatory growth was not exhibited when the second recovery period was reestablished. Any possible impact of the double cycle of intermittent starvation on energy reserves and structure of the hepatopancreas was compensated by a posterior cycle of continuous feeding. The results demonstrated that M. borelli can successfully support long-term food scarcity throughout the juvenile and adult phases, at least intermittently and followed by a recovery period. The high nutritional flexibility is an adaptation to fluctuations in food availability and an advantage for successful ornamental aquaculture.

Regeneration and growth that occur in the adult teleost retina have been helpful in identifying molecular and cellular mechanisms underlying cell proliferation and differentiation. Here, it is reported that S-phase cell number, in the ciliary marginal zone (CMZ) of the adult zebrafish retina, exhibits day-night variations with a mid-light phase peak. Oscillations persist for 24 h in constant darkness (DD), suggesting control by a circadian component. However, variations in the S-phase nuclei number were rapidly dampened and not present during and after a second day in DD. An ADPβS treatment significantly enhanced S-phase activity at night to mid-light levels, as assessed by in vivo BrdU incorporation in a 2-h interval. Moreover, daylight increase in S-phase cell number was completely abolished when extracellular nucleotide levels or their extracellular hydrolysis by ectonucleoside triphosphate diphosphohydrolases (NTPDases) were significantly disrupted or when a selective antagonist of purinergic P2Y1 receptors was intraocularly injected before BrdU exposure. Extracellular nucleotides and NTPDase action were also important for maintaining nocturnal low levels of S-phase activity in the CMZ. Finally, we showed that mRNAs of NTPDases 1, 2 (3 isoforms), and 3 as well as of P2Y1 receptor are present in the neural retina of zebrafish. NTPDase mRNA expression exhibited a 2-fold increment in light versus dark conditions as assessed by quantitative RT-PCR, whereas P2Y1 receptor mRNA levels did not show significant day-night variations. This study demonstrates a key role for nucleotides, principally ADP as a paracrine signal, as well as for NTPDases, the plasma membrane—bound enzymes that control extracellular nucleotide concentration, for inducing S-phase cell entry in the CMZ—normally associated with retinal growth—throughout the light-dark cycle.