# Mediterranean Aquaponics: Fasting and Refeeding in a Polyculture Aquaponic System
## 4 Discussion
### Fish Growth Performance
Other studies have indicated that species such as _Salmo salar_ ([PERSON], 1758), _Aristichthys nobilis_ ([PERSON], 1845), _Gasterostes aculeatus_ ([PERSON], 1758) and _Acipenser dabryanus_ ([PERSON], 1869) achieve the same mean weight as those subjected to a program of fasting and refeeding [41; 49; 50; 51]. A number of fish species, including the gilthead seabream [48], sturgeon [41], and salmon [52], have been observed to exhibit accelerated growth following a period of starvation and subsequent refeeding. Furthermore, the findings of the present study indicated a markedly elevated specific growth rate (SGR) and weight gain (WG) in sea bass subjected to treatments B and C, in comparison to treatment A. The study reported in [53] documented that rainbow trout (_Oncorhynchus mykiss_, [PERSON], 1792) exhibited an analogous specific growth rate (SGR) under 2 (SGR: 2%/d), 4 (SGR: 2.2%/d), 8 (SGR: 1.7%/d), and 14 (SGR: 1.7%/d) days of fasting in comparison to fish subjected to no fasting (SGR: 2.1%/d). Nutrient digestibility and, consequently, the specific growth rate are influenced by a number of factors, including food intake, fish size, and water temperature. In compensatory growth experiments, a number of mechanisms have been identified as playing a role, including hyperhagia [21], the optimization of metabolic rate [54], protein biosynthesis [55], the adaptability of the endocrine system during restricted feeding, a reduction in the basal metabolic rate, and an improvement in the feed conversion ratio (FCR) [45]. The feed conversion ratio (FCR) was found to be significantly higher in treatment A than in treatments B and C (ANOVA, \(p\) < 0.05). [PERSON] et al. [56] reported a lower feed conversion ratio (FCR) for sea bass, with a range of 1.0 \(\pm\) 0.04 to 1.2 \(\pm\) 0.75. [PERSON] and [PERSON] [57] reported hyperplasia when juvenile gilthead seabream were subjected to two periods of fasting (1 day fasting, 3 days refeeding and 1 day fasting, 5 days refeeding). Compensatory growth feeding leads to hyperhagia. A reduction in food transit through the digestive tract has been observed to result in hyperphagia. Hyperphagia in animals allows the same or higher total food intake as an individual with no food restriction, thereby reaching the same size [58]. The protein efficiency ratio (PER) demonstrated notable discrepancies among the experimental treatments (ANOVA, \(p<0.05\)), suggesting that the sea bass were influenced by the dietary regimen implemented throughout the investigation. Ref. [43] also observed similar results, with PER values differing between the control and starvation treatments. In contrast, ref. [59] reported that there was no significant difference in the PER values between the control and the 7-day fasting treatments. However, in the feeding regimen applied for longer fasting periods (2, 3, and 4 weeks), the PER values demonstrated a decline as the number of fasting days increased. Significant differences were observed in lipid retention (LR) among the treatments (ANOVA, \(p<0.05\)), with the highest value observed in treatment A and the lowest in treatment B. These findings are comparable to those reported by [6; 31]. Specifically, ref. [6] shows that seabreams and sea bass that were fed daily without starvation showed a higher LR than fish that were subjected to 4 or 7 days of starvation. Ref. [31] reported that in fish fed with the lowest protein content diet (30%), the LR values ranged from 34.3 \(\pm\) 1.57% to 77 \(\pm\) 3.22%. _Diplodus puntazzo_ ([PERSON], 1792) exhibited higher LR values. During periods of food deprivation, energy consumption is reduced due to a decrease in the fish's locomotor activity. During the rearing period, the reduction in activity contributes to compensatory growth in the fish, with available energy being allocated to this process. In fish species such as the sea bass (\(D\). _labrax_), rainbow trout [60], and tilapia (_Oreochromis niloticus_, [PERSON], 175862) [61] that are in a state of starvation, lipids are broken down at a faster rate than other nutrients.