Water quality parameters of the experimental tanks
Water quality parameters are essential factors in aquaculture operations (Ahmed et al. 2007). The success of an aquaculture system relies heavily on maintaining appropriate water quality conditions (Bhatnagar and Devi 2013). Therefore, it is of utmost importance to monitor and manage water quality parameters during fish farming. The average values of key water quality parameters, including pH, dissolved oxygen (DO), total dissolved solids (TDS), total ammonia-nitrogen (TAN), and plankton density, were recorded over a 60-day rearing period are presented in Table 1 and it exhibited normal variations. No significant deviations were observed in the water quality parameters among the experimental tanks. The water temperature ranged from 14.5 to 25.1°C, with a mean value of 19.5–19.8°C, in accordance with prevailing agro-climatic conditions of Northeast India. These findings are consistent with earlier studies on fish culture in Northeast India (Das and Majhi 2014; Das 2018).
Water temperature is a critical factor influencing fish growth, survival, and feed utilization (Sahu et al. 2007). Optimal water temperature ranges between 24 to 30°C are generally recommended for maximizing fish growth and ensuring their survival (Ayyappan et al. 2019). However, the hilly ecosystems of Northeast India often face challenges in maintaining the required tropical temperatures for successful fish farming. Consequently, the aquaculture production and productivity in this region are not on par with the plains of the country (Das et al. 2021). In such circumstances, implementing improved management practices and selecting fish species adapted to the specific ecosystems can enhance the viability of fish farming in the region.
The pH of the tank water ranged from 7.4 to 9.6, with a mean value of 7.8-8. This pH range is considered optimal for fish (Debnath et al. 2015). During fish stocking, the pH of the water was initially high, around 9.4–9.5, likely due to the use of recently treated pond water with liming material. However, over time, the pH gradually decreased to a range of 4.7–7.6 due to water exchange and rainfall. The dissolved oxygen (DO) levels in the tanks remained within the range required for fish, which is typically 4–5 mg/liter (Debnath et al. 2020). The tanks that received conventional feed (CF) had slightly lower DO levels (4.2–5.6 mg/liter) compared to the tanks that received pellet feed (PF) (4.6–6.2 mg/liter). This difference could be attributed to feed wastage and the utilization of DO for the decomposition of the wasted feed. The total dissolved solids (TDS) level in the water remained within the normal range of 48.5–63.5 mg/liter (James, 2000). The tanks that received CF had higher TDS levels (58.6 mg/liter) compared to the tanks that received PF (48.5–58.5 mg/liter). This suggests that the use of CF resulted in a higher formation of dust particles in the water. The ammonia levels in the tanks ranged from 0 to 1 mg/liter, with a mean value of 0.25–0.50 mg/liter, indicating favorable conditions for fish survival and growth. The mean ammonia content was slightly higher in the tanks that received CF, indicating feed wastage and the formation of ammonia from the breakdown of feed nitrogen (Debnath et al. 2019).
Despite the cold water conditions, the study observed optimal production of planktonic mass in the tank water. This could be attributed to the availability of nutrients from the pond water used in the study. The plankton density ranged from 2100 to 2770.5 numbers per liter, indicating favorable conditions for fish farming. This falls within the recommended range of plankton density suggested by Bhatnagar and Devi (2013) for fish farming. Higher plankton density was observed in tanks that received conventional feed (CF) compared to tanks that received pellet feed (PF). This difference can be attributed to the increased leaching of nutrients from the CF, resulting in higher plankton growth. Plankton plays a crucial role in providing a natural food source for fish, contributing to their growth and overall health. The water color in tanks that received PF ranged from light green to dark green. This is a positive indicator as it suggests the presence of beneficial algae and a healthy aquatic environment. However, the water in tanks that received CF turned dark brown after a month of fish rearing. This discoloration could be due to the formation of dinoflagellates and brown algae (Ayyanppan et al. 2019), which might have been influenced by the composition of the CF used.
Table 1
The mean values of water quality parameters in different experimental tanks (CF- conventional feed; PF- pellet feed)
Feed
|
Feeding rate
|
Water quality parameter
|
Temperature (0C)
|
pH
|
DO (mg/l)
|
TDS (mg/l)
|
Ammonia-N (mg/l)
|
Plankton (numbers/L)
|
CF
|
2%
|
19.7 ± 5.1a
|
7.8 ± 1.5 a
|
4.8 ± 0.7 a
|
58.6 ± 4.4 a
|
0.5 ± 0.4 b
|
2770 ± 287 b
|
PF
|
2%
|
19.8 ± 5.1 a
|
7.9 ± 1.5 a
|
5.4 ± 0.7 a
|
53.2 ± 4.2 a
|
0.25 ± 0.2 a
|
2100 ± 155 a
|
4%
|
19.6 ± 5.2 a
|
8.0 ± 1.3 a
|
5.3 ± 0.8 a
|
52.6 ± 4.2 a
|
0.25 ± 0.2 a
|
2100 ± 137 a
|
6%
|
19.5 ± 5.3 a
|
7.8 ± 1.7 a
|
5.2 ± 0.5 a
|
54.2 ± 3.7 a
|
0.25 ± 0.2 a
|
2170 ± 132 a
|
Fish growth and survival
Fish growth, nutrient utilization, and yield are influenced by the composition of the diets provided (Tacon and De Silva, 1997; Kristiansen and Ferno, 2007). Therefore, it is important to tailor nutritional management accordingly. In this study, regardless of the various feeding treatments (CF and PF), L. rohita exhibited superior growth compared to L. gonius in all tanks. This can be attributed to the physiological advantages of major carp species over minor carp species. Furthermore, irrespective of the different feeding treatments, L. gonius demonstrated higher survival rates than L. rohita in all tanks. This may be due to the hardier nature of L. gonius, which is adapted to bottom-dwelling habitats. These findings align with previous studies on fish co-culture (Jena and Das, 2011; Jena et al., 2015). In comparison to the present study, Jena et al. (2011) reported the dominance of L. gonius over L. rohita in terms of both growth and survival in their rearing with L. fimbriatus and Puntius gonionotus. This could be attributed to a greater population of medium carps in the production system, resulting in L. gonius receiving complementary benefits from other species of their nature. Another reason could be the larger size of L. gonius at the time of stocking, which might have led to their dominance over the population of L. rohita since the stocking in their study. These findings underscore the importance of further research to understand the dynamics and characteristics of different fish species in mixed-culture systems.
The growth performances of fish indicate that the use of pellet feed (PF) yielded better outcomes compared to conventional feed (CF). The mean length and weight of both fish species showed consistent improvements across all tanks as the feeding rate of PF increased. At the time of harvesting, the mean length of L. rohita and L. gonius increased from 7.4 cm (at stocking) to 11.1 cm with CF and 11.4 to 12.4 cm with PF (2 to 6% feeding rate), representing a growth increment of 2.7 to 11.7%. Similarly, the mean weight of the fish increased from 5.9g (at stocking) to 10.5g with CF and 10.8 to 33.7g with PF, indicating a weight increment of 83–212% (Fig. 1). These findings suggest that feeding PF resulted in superior growth performance compared to CF in the co-rearing of L. rohita and L. gonius in this particular study. The use of PF in capsule form proved advantageous in fish as it facilitated easier consumption by the fish, while CF, being in dust form, posed challenges for fish to consume effectively. This led to higher wastage and leaching of nutrients when CF was used, resulting in inferior nutrition and growth compared to PF (Zishan et al. 2019). Studies conducted by Yaqoob et al. (2010) have also indicated that PF yields superior outcomes in carp culture in contrast to CF, although the effectiveness may vary depending on the fish species, species combinations, and the feeding rate implemented in the culture system (Jena et al., 2011). Interestingly, the mean water temperature in this study was around 20°C, which according to Xu and Rogers (1994), can lead to increased leaching of nutrients from conventional feed that typically sink in water. However, this finding contrasts with the results reported by Chiu et al. (2001). The study revealed a linear increase in average fish growth from 10.8g to 33.7g with the increase in feeding rate from 2–6% using PF. This linear increment suggests that fish consumed more feed in response to increased food availability (Honnananda et al. 2019). The maximum growth was observed at the 6% feeding rate, indicating the optimal utilization of feed nutrients by the fish for growth. These findings align with the results reported by Ahmed (2007) for L. rohita and Khan (2004) for C. mrigala, where maximum growth and feed utilization were achieved at feeding rates of 6–8% and 4–6% of fish biomass, respectively. However, the study did not estimate the fish's maximum voluntary feed intake as the feeding rate was limited to a maximum of 6%. Further research is recommended to investigate the point of maximum voluntary feed intake by L. rohita and L. gonius under the unique hill ecosystems of Northeast India.
The study findings demonstrated that the mean specific growth rate (SGR) of fish fed with PF was higher, ranging from 1–2.9% per day, compared to fish fed with CF, which exhibited an SGR of 0.96% per day. Furthermore, within the PF-fed group, increasing the feeding rate from 2–6% resulted in a corresponding increase in SGR from 1–2.9% per day (Fig. 2). It is important to note that although there was a significant improvement (p ≤ 0.05) in SGR using PF, these values are relatively lower than those reported for the rearing of L. fimbriatus, L. gonius, and P. gonionotus with L. rohita, where SGRs typically range from 4.4–5.5% per day (Jena et al., 2011). This difference could be attributed to the higher feeding rate (6 to 8%) employed in their experiment compared to our study (2%). The availability of affordable feed is a major constraint in fish farming in Northeast India, which is why we restricted the feeding rate to a maximum of 6% of fish biomass per day. Another factor contributing to the lower SGR could be the relatively low water temperature ranging from 19.5°C to 19.8°C (Table 1). Suboptimal temperature conditions can influence the metabolic rate and feed utilization efficiency of the fish, leading to lower growth rates. To enhance SGR and maximize growth potential, further research is recommended to explore strategies such as optimizing temperature conditions or implementing alternative feeding methods in order to improve fish growth in the given environment.
When using conventional feed (CF), the biomass yield in L. gonius was higher (460g/tank) compared to L. rohita (420g/tank). However, when using pelleted feed (PF), the biomass yield in L. rohita (523.2 to 1636.2g/tank) was higher than the biomass yield in L. gonius (460 to 1368g/tank). This difference in biomass yield can be attributed to the feeding behavior of the two species. L. gonius typically feeds from the bottom of the aquatic ecosystem, and with CF being a sinking feed, it is more readily available to them, resulting in a higher biomass yield in tanks that received CF. On the other hand, L. rohita feeds from the surface to the column of the aquatic ecosystem, and with PF being a floating feed, it is more accessible to them, leading to a higher biomass yield in tanks that received PF. It is worth noting that studies conducted on catfish have shown inconsistent results when comparing floating and sinking diets in terms of their effects on growth, nutrient utilization, and yield (Ajani et al. 2011; Limbu 2015). These discrepancies highlight the need for further studies in this field to uncover the underlying causes and provide a clearer understanding of the effects of different feeding strategies on fish production.
The study findings revealed that fish fed with PF had a higher mean survival rate, ranging from 86.5–91.5%, compared to fish fed with CF, which exhibited a survival rate of 84.5% (Fig. 3). This is consistent with the results reported by Keshavanath et al. (2002) in the rearing of L. fimbriatus, another medium carp, where a survival rate of 85% was achieved after 60 days of rearing with CF composed of rice polish, mustard oil cake, etc. The use of PF, coupled with proper feeding and management practices, contributed to the improved survival of fish (Honnananda et al. 2019). These findings underscore the significance of employing appropriate feeding strategies and effective management techniques to enhance fish survival rates.
The use of PF resulted in a lower feed conversion ratio (FCR) compared to CF, with FCR values of 1.4–1.45 for PF-fed fish and 1.6 for CF-fed fish (Fig. 4). It appears that CF feeding led to feed wastage and longer feeding time, contributing to poor FCR (Tvenning and Giskegjerde 1997). Similar results in C. mrigala, where CF feeding was found only met energy requirements but did not promote growth (Khan et al. 2004). These findings highlight the superior feed utilization and efficiency of PF, leading to improved growth and cost-effectiveness in fish farming.
The regression parameter (b) of the regression equations provides insights into the health status and well-being of fish, with higher condition factors indicating better overall condition in their habitats (Froese et al. 2006). A b value of 3 indicates isometric fish growth and ideal condition, while a b value < 3 suggests negative allometric growth, and a b value > 3 indicates positive allometric growth (Pauly 1983). In this study, CF-fed fish had a b value of 2.8 (2.7–2.9), indicating negative allometric growth, while PF-fed fish had a b value of 3.1 (2.2–4.2), indicating positive allometric growth (Fig. 5). These findings align with the results reported by Limbu (2015) and suggest that PF-fed fish exhibited improved energy reserves in fish, likely attributed to the implementation of effective feeding strategy in their production system (Chellappa et al. 1995).
VSI and HSI provide valuable insights into the digestion, absorption, and nutritional status of fish (Pérez-Jimenez et al. 2007). In this study, CF-fed fish had a mean HSI of 0.42%, while PF-fed fish had HSI ranging from 0.93–1.87%, an improvement. With PF feeding, HSI increased as the feeding rate increased from 2–6% (Fig. 6). The mean VSI was estimated to be 3.14% in CF-fed fish and 4.1–7.6% in PF-fed fish. Similarly, VSI increased with the increase of feeding rate from 2–6% in PF-fed fish (Fig. 7). The improvement in HSI and VSI suggests that the fish were able to accumulate feed nutrients in their flesh (Babalola et al. 2022). This also indirectly indicates improved nutritional status and better condition in fish (Chellappa et al. 1995).