Duckweed (Lemna minor) meal as partial replacement for fish meal in catfish (Clarias gariepinus) juvenile diets

Arnold Ebuka Irabor, Oghenebrorhie Obakanurhie¹, Francis Oster Nwachi, Paterson Adogbeji Ekokotu, Jerimoth Kesena Ekelemu, Ovie Kingsley Awhefeada, Lydia Mosunmola Adeleke², Hardin Pierre Jrn³ and Oghenefejiro Adagha

Department of Fisheries and Aquaculture. Delta State University, Abraka
iraborarnold@gmail.com
¹ Department of Animal Sciences. Delta State University, Abraka
² Department of Fisheries and Aquaculture Technology. Federal University of Technology, Akure
³ Ministry of Fisheries, Saint Lucia

Abstract

The present study examined the effect of duckweed (Lemna minor) meal inclusion levels (0%, 20%, 40%, 60% and 80%) on the growth, blood and serum profiles of C. gariepinus juvenile cultured for 56days under well managed condition. Proximate analysis on the test ingredient revealed a significantly (P≤ 0.05) high crude protein content in the test ingredient. At the end of the experiment, data evaluated revealed that at 40% duckweed meal inclusion level significant (P≤ 0.05) increase in growth was observed in C. gariepinus juvenile, while as inclusion level increased (60% and above), decline in the growth rate was observed. The test diets had no negative impact on the blood and serum profile of the sampled fish because all parameters observed were within the normal range. The water quality parameters examined revealed no adverse effect of the test diets on the water quality. Conclusively, 40% inclusion level of duckweed meal in the diet of C. gariepinus juvenile is best for optimum growth performance without any adverse effect.

Keywords: feed formulation, Lemna minor, nutrient, performance

Introduction

Catfish culture has overtime become the desire of most fish farmers due to its continuous increasing demand (Ganesh et al 2021). As the world’s campaign for the consumption of less fatty food continues to intensify, people consider fish and its products as a reliable and affordable option for required protein (FAO 2021; WHO 2021; Henchion et al 2017). However, due to the high cost of fish feed resulting from cost and scarcity of ingredients, there has been a shortfall in fish production (Hua et al 2019). In a bid to cutdown production cost, farmers sought to replace the expensive fish meal with alternative plant protein sources (Gasco et al 2018; Ayadi et al 2012).

Duckweed (Lemna minor) is one among the numerous species of Lemnaceae family found in the freshwaters of tropical and sub-tropical regions. It is a greenish passive aquatic plant with floating roots less than 1 cm in length and fronds ranging a few centimeters in width (Iqbal et al 2019). This aquatic plant is easy to grow due to its regenerative characteristic and can be blown to nutrient-rich areas by wind. Spontaneous growth of duckweed is commonly achieved in ponds, ditches, or swamps with abundant nutrients (Marcin et al 2019; Khellaf and Zardaoui 2010). In addition, duckweed is known for its rapid growth and long-lasting freshness which has informed its wide range of uses (Baek et al 2021).

Duckweed contains very significant levels of protein (40 – 43% dry weight), phosphorus, potassium, minor minerals and amino acids profile, superior to other plants (Stadtlander et al 2019). Furthermore, it has other qualities such as a low fibre content (5% in dry matter), which makes it readily digestible. Its production rate averages about 30 tons yearly of dry matter/ha which is dependent on nutrients availability, species, management, space and climate (Cao et al 2018).

The replacement of fishmeal with duckweed in catfish diet as one of the main protein sources is prominent, therefore this study examined how different quantities of fishmeal substituted for duckweed meal affected the performance of Clarias gariepinus juveniles.

Materials and Methods

Study area

The two phases study was done in the Research farm and Aquaculture lab both in Delta State University, Asaba. Asaba is one among the prominent local government areas that makes up Oshimili South. Latitudinal and longitudinal description are within 4⁰N to 10⁰N and 6⁰E to 8⁰E respectively.

Feed ingredients

Prior to the formulation of the experimental diets, all necessary feed ingredients apart from the duckweed (Table 1) were procured from the popular Akwaza market Asaba metropolis, Delta state and milled into mixture. The test ingredient (duckweed) was identified and harvested from well-managed earthen ponds specially reserved for the purpose, dried at room temperature, crutched into powder preserved in sealed flask. In the right percentages (20%, 40%, 60% and 80%), the duckweed meal (D) was mixed with other ingredients and pelleted into 2mm fish feed using an automated pelletizer.

Photo 1. A. Duckweed in waterbody; B. Formulated pellets

Experimental design and sample collection

The total fish samples used for the study were one thousand five hundred (1500) healthy C. gariepinus juvenile sourced from the University Research Farm. The initial weight (9.5g) and length (7.2cm) of the fish was ascertained to the nearest 0.1 error margin using sensitive balance and meter rule respectively. To reduce the effects of stress, fish samples were immersed for 20mins in 2-ppm sodium per manganate solution before stocking into well aerated concrete tank measuring 8 m X 6 m X 3 m and twice/day feeding routine (7:00 am and 6:00 pm) using Ziglar feed (2 mm) 14 days prior to the start of feeding trial.

The fish samples were stocked in quadruplicate of seventy-five (75) C. gariepinus juveniles per rearing tank measuring 4 m X 2 m X 1.3 m with well oxygenated water. According to the experimental diets to be administered, tanks were well labelled D_1-4 0% (control), D_1-4 20%, D_1-4 40%, D_1-4 60%, and D _1-4 80%. Although the control tanks were fed same experimental diet but with D 0% inclusion level. The formulated diets were administered appropriately at a 5% body weight twice/day (7:00 am and 6 pm) and proper water quality management was adhered.

Sample measurement to determine the fish growth parameters was done biweekly, while the haematological profile, serum and carcass quality of the sample were conducted in conclusion of the feeding experiment (56days). Growth parameters were determined using sensitive scale for weight and calibrated meter rule for length. Stress resulting from the sampling exercise was minimized using harvest techniques are recommended by Irabor et al (2021).

Compounding the diets

Fish feed of 40% crude protein was formulated from the composition of the feed ingredients (Table 1)

Study duration

The study lasted for a period of 56 days (September to November, 2021).

Evaluation of feed utilization and growth indices

Feed utilization which includes feed conversion ratio and feed intake as well as growth indices such as body weight gain were calculated using the method as described by Irabor et al (2021). Survival rate was also determined using the method as described by Limbu (2020).

Blood and serum evaluation

The blood profile was examination was carried out using the methods as described by Kone et al (2017) and Anand et al (2020). This was to determine the effect of the test ingredient on the blood and serum profile of the sampled fish.

Water quality

The readings of some significant physicochemical parameters were examined using the methods as described by Muna et al (2021).

Statistical Analysis

The data obtained from the study were subjected to statistical analysis using ANOVA as the tool from SPSS version 25, while the means were differentiated using Duncan multiple range tests at P≤ 0.05 level of significance.

Results

Proximate analysis was conducted on the test ingredients (duckweed) and results presented in Table 2. The test ingredient revealed a significantly high crude protein level (41.08%).

The proximate composition of the test diets was ascertained and presented in Table 3. Diet with 40% inclusion level of the test ingredient had the highest crude protein level (40.47%), while the lowest crude protein level (32.71%) was observed in 80% inclusion of duckweed.

The differences in growth parameters and diets utilization were presented in Table 4. The highest body weight (35.52g) and survival rate (96%) were recorded at DWM 40% inclusion level, while the lowest (24.29g) and (68%) respectively, were observed in 80% inclusion level. The best value for feed conversion ratio (1.98) was observed at DWM 40% inclusion level, while that of 80% inclusion level was poor (2.65).

Figure 1. Relationship between feed intake and duckweed in the diet DM in diets	Figure 2. Relationship between live weight gain and duckweed level in the diet

Figure 3. Relationship between feed conversion and duckweed diets	Figure 4. Relationship between survival rate and duckweed in diets

The blood and serum profile of the sampled fish was evaluated at the end of the experiment and the results was presented in Table 5. All parameters were within normal. However, there were slight increase and decrease amongst parameters as inclusion levels increased.

The carcass of the sampled fish revealed significant (P≤ 0.05) decrease in crude lipid and crude protein as D inclusion levels increased in the diets, while other parameters showed significant (P≤ 0.05) increase (Table 6).

Some of the physicochemical parameters of the culture media were observed and presented in Table 7. The values recorded showed pH and DO values were highest in tank fed 0% inclusion level of test ingredient, while the lowest was observed at 40% inclusion level. Temperature value was highest at 60% inclusion level, while 0% inclusion level had the least value.

Discussion

The values observed from the proximate analysis revealed on the test ingredient (duckweed) ranged between the values reported by Ullah et al (2021). The proximate composition of the diets showed significant (P≤ 0.05) difference as test ingredient inclusion in the diets increased especially the crude protein level which was higher compared to soyabean meal making it a potential plant protein source for fish feed (Hameed et al 2020).

The experimental diets had crude protein levels within the acceptable range 35 – 45% for the culture of C. gariepinus juvenile. This confirmed the findings of Radulović et al (2021) and Leng et al (1995) where a crude protein of 40 and 43% was recorded respectively in formulated catfish feed with DWM as additive.

Growth performance and feed utilization revealed a significant increase in weight of C. gariepinus juvenile fed diets as percentages of DWM increased. Although there was also significant decline at 60% and 80% DWM inclusion levels. The improved growth observed was attributed to the optimum nutrients and low fibre (below 10%) content present in the DWM. This confirms the reports of Yuniel et al (2021) who attributed the recorded increased growth rate in C. gariepinus fingerlings fed diets with varying levels of duckweed meal as additives to the high nutrient and low fiber content of duckweed. However, the decrease in growth observed at inclusion levels 60% and above can be attributed to poor feed utilization. Same was observed as DWM inclusion levels increased to 50% in Nile tilapia feed (Tavares et al 2008).

Feed intake recorded showed a proportionate decline as DWM inclusion levels increased across treatments. This could be linked to the digestibility, palatability and nutrient of the diets as inclusion levels increased to 60% DWM and above. This is similar to the findings of Yuniel et al (2021) who reported significant decrease in feed intake as inclusion levels of duckweed meal (Lemna perpusilla) in diets of C. gariepinus fingerlings. Also, Olaniyi and Oladunjoye (2012) recorded decline in the feed acceptability in O. niloticus as inclusion levels of duckweed meal (Lemna minor) increased to 50% and above.

The blood and serum profile of the sampled fish were within the normal range which indicated DWM had no adverse effects on C. gariepinus juveniles. Although, significant increase and decrease was observed in the parameters examined as DWM inclusion levels increased. This can be attributed to the antioxidant characteristics of duckweed. A similar finding was recorded by Irabor et al (2021) where moringa leave meal as feed additives caused significant fluctuation in the blood profile of C. gariepinus juveniles. Also, Xuhui et al (2020) recorded a proportionate decrease in the blood and serum indices as inclusion levels of fermented moringa leave meal increased in diets of Carassius gibelio juvenile.

Carcass quality of C. gariepinus juvenile revealed the impact of DWM inclusion in the diets. A corresponding increase in the values of NFE, crude fibre and moisture content of the carcass was observed as DWM inclusion levels increased. Although, crude protein and fibre values decreased as DWM inclusion levels increased. This could be linked to the effects of NFE, moisture and fibre contained in duckweed. Same results were recorded in the carcass of C. gariepinus juvenile fed diets with varying inclusion levels of moringa leaf meal (Irabor et al 2021).

Water quality parameters of the culture tanks were not influenced significantly by the test ingredient (DWM). Temperature, pH and dissolved oxygen across the treatments were all within acceptable range. However, there were insignificant changes in the water qualities examined across treatments as DWM inclusion increased. This also contributed to the performance of the sampled fish due to favorable environmental condition. This confirmed the finding of Huong et al (2020) who reported optimum growth of Chitala ornate reared in culture tanks with average temperature between 30 – 32 ^oC. A contrary record was given in Islam et al (2020) who recorded minimal growth of Dicentrarchus labrax as inclusion levels of moringa leave meal increased in the diets. Although, the poor growth was linked to stress resulting from turbid water caused by excess waste (uneaten feed).

Conclusion

• At 40% DWM inclusion level, feed intake, and conversion ratio were optimal.
  
  
• Optimum performance of C. gariepinus juvenile was observed at 40% DWM inclusion levels in the diets.
  
  
• DWM had impact on the blood and serum profiles of C. gariepinus juvenile and some of the water quality parameters.

Acknowledgements

We wish to acknowledge the entire staff of Fisheries Department, Faculty of Agriculture, Delta State University, Abraka for their immeasurable support via supply of necessary materials for this work.

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