Algae meals may provide fishmeal, oil replacements for carnivorous fish

Replacing some fishmeal and oil use with algae meal may boost the weight gain of carnivorous fish and alter fish fatty acid profiles while supporting fish survival, say researchers.

Whether algal meals could be used in place of fishmeal or soy protein concentrate (SPC) and fish oil in the diet of farmed striped bass was the question posed by an international team of researchers from Mexico and the US.

“The present study sought to evaluate the use of the heterotroph S. limacinum and the autotroph Arthrospira sp. in feeds for juvenile hybrid striped bass,” ​the researchers said.

In the feeding trials, the researchers showed that the algal-based ingredient could support fish production, and that fish receiving diets with 30% and 50% replacement of fishmeal, fish oil and soy protein concentrate had higher weight gain than those on a control diet. Fish on the algal-based diets also had higher levels of docosahexaenoic acid (DHA) in their tissue.

“The combination of Arthrospira sp. and S. limacinum meals can replace a significant proportion of fish-derived feedstuffs in hybrid striped bass feeds, promoting suitable growth performances with up to 50% replacement under these conditions, and promoting the accumulation of DHA in fish tissues, which would ultimately benefit consumers,”​ they added.

Why replace fishmeal and oil?​

Aquaculture production is one way to support the increasing global demand for seafood, but there are challenges especially in the limited supplies of fishmeal and fish oil needed to generate feeds for carnivorous fish, the researchers said.

Fishmeal provides a high level of protein and balanced amino acids and fish oil brings long-chain polyunsaturated fatty acids (LC-PUFA), they said. However, limited availability increases the price for these feed ingredients.

Alternative feed ingredients are being tested for use in feeds for carnivorous fish, they said.

“Alternative sources of protein to fishmeal frequently include vegetable or animal meals, such as soybean meal, soy protein concentrate, corn gluten meal, blood meal or poultry by-products, among others, while soy, canola, or linseed oils are some of the sources frequently used to replace fish oil,”​ they added.

“Replacement of fishmeal and fish oil, however, is often limited by potential problems associated with insufficient levels of essential amino acids or fatty acids, the presence of anti-nutritional factors or poor palatability,”​ the researchers said.

Feed ingredients made from microalgae are of increasing interest as some species of algae have high levels of needed nutrients including proteins and lipids, they said.

“Arthrospira sp., formerly called Spirulina, has a high protein content, in addition to essential fatty acids, vitamins, minerals and polysaccharides,” ​they said. “Schizochytrium limacinum on the other hand, is an exceptionally good source of docosahexaenoic acid (DHA, 22:6n-3).”​

Microalgae also can be raised in controlled processes making some strains sustainable to generate and use in place of fishmeal and oil, they said. Arthrospira sp. meal has been used in diets for tilapia, parrot fish, rainbow trout and red drum, while S. Limacinum​ has provided a fish oil alternative in diets for giant grouper and S. ocellatus.​

Hybrid striped bass is a carnivorous fish increasingly raised in aquaculture scenarios, the researchers said. However, little is known about the use of microalgae-based feed ingredient in diets for the fish.

Feeding trial highlights​

In the feeding trial, 216 juvenile hybrid striped bass had a two week- acclimation period in a recirculating production system on a diet with 40% crude protein and 12% crude fat, the researchers said. Fish were then transitioned to the trial’s control diet, which included fishmeal (FM), soy protein concentrate (SPC) and fish oil (FO) for two weeks.

Following the acclimation process, fish received one of six diets for a six-week period, they said. The diets included the control, and “five more diets were formulated to replace 10, 20, 30, 40 and 50% of FM, SPC, and FO in the control diet by untreated meals derived from Arthrospira sp. (Spirulina) and S. limacinum.”​

Experimental feeds also were supplemented with lysine, DL-methionine and taurine to match levels found in the control diet, they added.

Fish were weighed and sampled at the start of the feeding trial for whole-body analysis and remaining fish were weighed weekly during the feeding trial, the researchers said. Fish also were weighed at the end of the feeding trial.

Fish survival and feed use were determined at the end of the feeding trial and growth performance, hepatosomatic index (HSI) and protein efficiency ratio (PER) were calculated, they said. Select fish were harvested, weighed, measured, dissected and liver weight, intraperitoneal fat, condition factor and fillet muscle were recorded.

Collected fish also were analyzed for crude protein, crude fat, ash, and whole-body moisture were determined, they said. They also were checked for fatty acid presence.

Results ​

Survival rates were the same for fish on all diets, and weight gain was similar for fish on several diets, however, fish on the 30% and 50% replacement diets outweighed and had larger thermal growth coefficient (TGC) than those on the control feed, the researchers said. 

Condition factor, HSI and intraperitoneal fat were similar for fish on all diets, but muscle ratio (MR) was much lower for fish on the control diet than those on the experimental feeds, they said. Feed use indices were similar for fish on all the diets.

“The largest PER (2.70 g g−1) was observed in fish fed the 40% replacement diet, and the lowest values were observed in those fed the control (2.43 g g−1) and the 10% replacement diet (2.50 g g−1); similarly, the largest [protein retention] PR (53.1%) was observed in fish fed the 40% replacement diet, and the lowest (45.5%) in the control group,”​ they said.

Fish on the 30% replacement diet had the largest amount of crude fat and the fish with the least were on the 50% replacement diet and the control, the researchers said. Other proximate composition areas including crude protein, moisture and ash were similar for all fish.

Fish on the replacement diets also had different fatty acid composition and displayed increasing levels of palmitic acid, total saturated fatty acids and DHA, they said. However, eicosapentaenoic acid (EPA), oleic acid and other monounsaturated fatty acid levels in fish fell as more fish oil was replaced.

“Fish fed the control diet showed the highest n-3/n-6 ratios in whole-body tissues, indicating that, in spite of the contribution of DHA from S. limacinum meal to the total n-3 fatty acids, as a general trend, replacement of FO decreased the rest of the n-3 fatty acids, e.g., EPA, eicosatretraenoic acid (20:4n-3), stearidonic acid (18:4n-3), and alpha-linolenic acid (18:3n-3),”​ they added.

Source: Aquaculture​

Authors: M. Perez-Velazquez, D. Gatlin III, M. González-Félix, A. García-Ortega, C. de Cruz, M. Juárez-Gómez, K. Chen