In terms of dietary composition, protein is the single largest and most expensive component in fish feed. A feeding trial was conducted to determine the maximum substitution limits of poultry by-product meal protein for fish meal protein in the diet of juvenile Black Sea Bass Centropristis striata. Results showed poultry by-product meal as a promising alternative protein source for sustainable diet development in Black Sea Bass.
In terms of dietary composition, protein is the single largest and most expensive component in fish feed. Fish meal (FM) is a source of high-quality protein and highly digestible essential amino and fatty acids, making it a popular source of protein in aquaculture feeds.
“Worldwide production of FM has been stable at roughly 6.3 million metric tons annually since the 1980s. Once seen as a renewable source, FM costs have increased as demand has increased, while supply has slowly decreased due to overfishing.”
In addition, FM varies greatly in composition and quality among species or with age, season, geographic origin, and processing methods. Therefore, it is critical to investigate alternative protein sources to FM protein in aquaculture feeds.
Terrestrial animal protein sources have several advantages, including a similar amino acid profile to FM, availability, and relatively low cost.
The two most common chicken ingredients in pet feed are poultry meal and poultry by-product meal (PBM). PBM is a protein source produced from waste and by-products of processed chickens. It has been used successfully to replace FM at high levels of dietary inclusion for a number of finfish species.
“Black Sea Bass is a commercially important marine finfish species inhabiting coastal waters of the eastern USA, from the Gulf of Maine to Florida that commands a high market value. Its abundance along the U.S. East Coast has been declining since the1950s and stringent quotas are in effect for harvesting of wild populations.”
Potential for limited market supplies and for higher prices of ocean caught Black Sea Bass in the future are important economic incentives to investigating the feasibility of Black Sea Bass production via aquaculture to help meet market demand.
Here we present a study conducted to determine under controlled laboratory conditions the maximum substitution limits of the animal protein source PBM for FM protein in juvenile Black Sea Bass diets and the effects of replacement on whole body and muscle tissue proximate composition.
Experimental animals and system
Juvenile Black Sea Bass were cultured from eggs spawned by photothermally conditioned broodstock held at the University of North Carolina Wilmington Aquaculture Facility (Wrightsville Beach, North Carolina).
Broodstock were induced to spawn using luteinizing hormone-releasing hormone analog implants. Eggs were hatched and reared through the juvenile stage in 150-L tanks.
“The experimental system consisted of 24 75-L rectangular (76 cm × 32 cm × 43 cm) glass tanks supported by a recirculating seawater system located in a controlled-environment laboratory.”
Water quality was maintained by a bead filter, a foam fractionator, and a UV sterilizer.
Tanks were subjected to a 12 h light: 12 h dark photoperiod supplied by eight 60-W fluorescent lamps in addition to ambient light levels from sunlight entering the laboratory windows.
Experimental diets and feeding protocol
Eight diets were formulated to replace FM protein with pet-feed-grade PBM protein at levels of 0 (control), 40%,50%, 60%, 70%, 80%, 90%, and 100% (Table 1).
All diets were formulated to have the same crude protein level (44%) and lipid level (13%). The analyzed crude protein levels in the test diets are showed in Table 1. Except for wheat gluten as a binder, no additional protein sources, amino acids, or attractants were used.
“All diets contained the same amount of vitamin and mineral premix. Atlantic Menhaden fish oil and soybean lecithin were used as lipid sources in addition to the lipid content found in the protein sources.”
Treatment diets were fed twice daily (0900 and 1500 hours) to triplicate groups of juvenile Black Sea Bass to apparent satiation (i.e., as much as fish could consume without wastage) for 8 weeks.
Proximate composition of diets and fish tissues
At the end of each experiment, 8–10 fish from each tank were collected for biochemical analysis. Five fish were used to determine proximate composition (moisture, ash, lipid, and protein) and fatty acid profiles of the whole body and from three to five fish were dissected to analyze the proximate composition of muscle tissue.
Results and Discussion
Survival and Growth
At the end of the experiment on day 56, survival ranged from 95% to 100%, with no significant (P > 0.05) differences among treatments (Table 2).
No significant differences in mean fish weights (range = 1.1–1.3 g) were observed among treatment groups at the beginning of the experiment (day 0) (Figure 1). By day 14, fish mean weights ranged from 4.1 to 4.3 g, with no significant differences.
On day 28 and day 42, fish fed the 100% PBM protein diet were significantly smaller (6.6 g and 9.9 g, respectively) than fish fed the control FM diet (7.9 g and 13.0 g, respectively). At the end of the experiment (day 56), fish weight in the 100% PBM protein diet was significantly lower (13.6 g) than in the control FM protein diet (17.8 g) (Table 2).
Survival of juvenile Black Sea Bass in all diet treatments was excellent throughout the experiment with little or no mortality. This is similar to what has been reported in other carnivorous marine finfish species, which showed high survival when fed diets with FM protein replaced by PBM protein at levels of 20–100%.
No significant differences in feed intake were observed, which ranged from 0.26 to 0.30 g/fish/d (Table 2). Feed conversion ratios (FCRs) for fish fed the 60% PBM protein diet (1.17) and the 100% PBM protein diet (1.19) were significantly higher than fish fed the control FM protein diet (0.99) (Table 2).
Feed intake in juvenile Black Sea Bass did not differ significantly among treatments, suggesting that palatability was not affected by substitution of PBM protein for FM protein in the treatment diets.
Fish whole body and muscle tissue proximate composition
Fish whole body moisture content ranged from 63.5% to 66.2% among treatments (Table 3).
Whole body moisture content of fish fed diets with 50–80% PBM protein (65.6–65.8%) and 100% PBM protein (66.2%) was significantly higher than in fish fed the control FM diet (63.5%). Fish whole body ash content ranged from 4.49% to 6.37% (Table 3) among treatments.
No significant treatment differences were observed in fish muscle moisture (75.5–76.4%), ash (1.29–1.34%), or crude protein (18.1–20.1%) content (Table 4).
The muscle tissue crude lipid level of fish fed the 50% PBM protein diet (3.4%) was significantly higher than in fish fed the control FM protein diet (2.7%) (Table 4).
Whole body moisture content was significantly higher in Black Sea Bass fed diets with 50–80% and 100% PBM protein. Whole body ash content increased with increasing levels of PBM protein in the diet while moisture, ash, and protein content of the muscle tissue showed no significant differences among fish fed the different diet treatments.
Fatty acid profile of the diets and whole bodies
Although total lipid content of the whole body was not significantly different between fish fed PBM protein and FM protein, the composition of fatty acids in the whole body reflected dietary levels of the terrestrial animal and marine protein sources used.
Oleic acid (n-9: number of the carbon atoms in the compound) levels increased with increasing PBM protein in the diet, causing a corresponding increase in total monounsaturated fatty acid (MUFA) concentrations with increasing PBM protein. Clearly, PBM contains higher MUFAs than FM, and high levels of dietary PBM produced high amounts of MUFAs in the whole body of juvenile Black Sea Bass.
“This same trend was observed in linoleic acid (n-6) and the sum of n-6 polyunsaturated fatty acids (PUFAs) in the whole body of juvenile Black Sea Bass. Similarly, juvenile Coho Salmon Oncorhynchus kisutch fed a diet completely replacing FM protein with PBM protein contained elevated oleic acid, total MUFA, linoleic acid, and total n-6 PUFA levels (Twibell et al., 2012).”
In the present study, fish fed the 100% PBM diet showed the lowest growth performance, and this may also be due in part to the relatively low dietary levels of essential fatty acids, particularly the long-chain n-3 polyunsaturated fatty acid (PUFAs), (n3) eicosapentaenoic acid (EPA), and (n-3) docosahexaenoic acid (DHA).
The lipids present in the poultry meal are generally rich in MUFAs (particularly oleic acid) and total n-6 PUFAs but are low in n-3 PUFAs, EPA, and DHA (Higgs et al., 2006). The PBM protein can be included up to a level of 44% in diets for juvenile Rainbow Trout without a decrease in EPA and DHA in whole body tissues (ParesSierra et al., 2014).
“Given the trend toward lower dietary n-3 PUFAs with increasing incorporation of PBM protein, the comparable levels of n-3 PUFAs in whole body tissues among all diet treatments are noteworthy and may suggest that dietary n-3 PUFA requirements were met under all diet treatments.”
This supports the idea that growth inhibition in the 100% PBM protein diet may have been due to an amino acid deficiency. Fish fed the 50% PBM protein diets showed much higher whole body EPA, DHA, and n-3 PUFAs than the fish fed the others diets, but this was possibly due to the inadvertent selection of bigger fish for fatty acid analysis in that diet treatment.
The PBM used in the present study had higher lipid content than the FM, so less fish oil was added as PBM was increased in the diets to maintain the diets isolipidic.
Hence, the diet replacing 100% FM protein with PBM protein contained 1.2% less fish oil than the high FM based control diet. Since PBM is low in n-3 PUFAs, the substitution of PBM protein for FM protein and the incremental reduction of fish oil reduced EPA and DHA levels in the diets.
“However, growth performance was not impaired up to a substitution level of 90% PBM protein. The EPA and DHA levels for the diets replacing up to 90% FM protein with PBM protein met or exceeded the minimum recommended dietary levels for other marine fish, such as Red Seabream Pagrus major and Yellowtail Seriola quinqueradiata (Sargent et al., 2002).”
A significantly lower n-3 to n-6 PUFA ratio in the whole body of Black Sea Bass fed PBM-based diets compared with the fish fed control FM protein diet was also observed in this study. Replacing FM protein with PBM protein in the diets of Black Sea Bass also did not affect the ratio of DHA to EPA (0.84–1.01) found in the whole body, a level which was above the dietary requirement for Yellowtail (0.5) (Sargent et al., 2002).
No recommended level of EPA or DHA in the diet for Black Sea Bass has been published. However, based on the EPA and DHA levels in the diets in this study and the reported requirements for other marine species, sufficient EPA and DHA were provided in all the diets replacing FM protein with PBM protein.
Also, the apparent digestibility coefficients (ADC) of protein ranged from 82% to 84%, which is similar to values reported for other species.
The results demonstrated that FM protein can be replaced by feed-grade PBM protein in juvenile Black Sea Bass diets at levels as high as 81.8% without adversely affecting survival, growth, feed utilization, fish biochemical composition, or ADC of protein or lipid. Poultry byproduct meal is a highly effective protein source for alternative protein-based feed formulation for Black Sea Bass.
This is a summarized version developed by the editorial team of Aquaculture Magazine based on the review article titled “EVALUATION OF POULTRY BY-PRODUCT MEAL AS AN ALTERNATIVE TO FISH MEAL IN THE DIET OF JUVENILE BLACK SEA BASS REARED IN A RECIRCULATING AQUACULTURE SYSTEM” developed by MATTHEW R. DAWSON, MD SHAH ALAM, WADE O. WATANABE, PATRICK M. CARROLL and PAMELA J. SEATON – University of North Carolina Wilmington.
The original article was published in NORTH AMERICAN JOURNAL OF AQUACULTURE in FEBRUARY, 2018.
The full version, including tables and figures, can be accessed online through this link: DOI: 10.1002/naaq.10009