Use of Krill Hydrolysate as a Feed Attractant for Fish Larvae and Juveniles

Abstract.— We determined the effect of krill hydrolysate as a feed attractant in three freshwater fish species: yellow perch Perca flavescens . walleye Stizostedion vitreium . and lake whitefish Coregonus clupeaformis . Growth trials were conducted using a commercial trout starter diet (control) and the diet that was coated with liquid krill hydrolysate. The krill hydrolysate coated diet increased growth of yellow perch juveniles by 31% compared to control diet (average final wet weight, 734 ± 33 mg and 559 ± 82 mg, respectively). Moreover. weight gains were not significantly different than for tish Id exclusively live Artemiu nauplii. Similar results were obtained with walleye juveniles fed either a trout starter diet or 5% krill hydrolysate coated diet (8.9 ± 0.25 g and 11.6 ± 5.1 g wet weight, respectively). The food conversion ratio (FCR) was lower in fish fed the control diet, although not significantly different (2.95 ± 0.18 and 3.69 ± 0.39. for control and coated diet. respectively). The effect of krill hydrolysate on dry diet ingestion rates of lake whitefish and yellow perch larvae was also determined using radioactive (¹⁴C) labelling. A commercial starter diet was coated with krill hydrolysate or the soluble fraction of krill hydrolysate was added to the experimental tank water. In both species. coating the diet with 5% krill hydrolysate resulted in significantly higher ingestion rates. Supplementation of krill hydrolysate soluble fraction to the tank water resulted in 200% increase in ingestion rate in comparison to control (uncoated starter diet), although it was not significantly different from krill coated diet and live Artemia nauplii ingestion rates.     

The effect of dietary lecithin and lipase,as a function of age,on n-9 fatty acid incorporation in the tissue lipids of Sparus aurata larvae

The present study tested the effect of dietary lecithin and exogenous lipase on the incorporation of oleic acid in the tissue lipids of gilthead seabream larvae (Sparus aurata). Two of four microdiets were prepared by the addition of [¹⁴C]oleic acid as free fatty acid (FFA) to diets containing either 5% cuttlefish liver oil (CLO) or 5% soybean lecithin. Glycerol tri[1-¹⁴C]oleate was similarly incorporated in two other diets identical in lipid (4% cuttlefish liver oil, 1% soybean lecithin) and non-lipid composition but differed in that one contained a supplement of 0.05% porcine lipase. The effect of these diets was tested by following the incorporation of the label (dpm/mg larvae DBW) in the neutral and phospholipid fractions of seabream larvae at four different ages (21, 27, 32 and 45 days after hatching).A significant (p<0.05) effect of dietary lecithin on the incorporation of labelled FFA in both larval neutral and phospholipid fractions was demonstrated at all ages. This was particularly pronounced during early development (day 21) where fish fed the lecithin supplement incorporated 6.75 times more label than the diet containing [¹⁴C]oleic acid in CLO. The dietary lecithin enhancing effect diminished with age but was still significant at day 45 (2.17 times more label). In addition, the label was considerably higher in the phospholipid fraction compared to the neutral lipid, reflecting the high demand for membrane synthesis during rapid growth. Lecithin fed larvae demonstrated a higher consumption rate and efficiency of incorporation than fish consuming the cuttlefish liver oil diet, suggesting an emulsifying function for dietary phospholipid.In contrast, the supplementation with lipase showed a clear effect only in older fish where 45 day old larvae fed the lipase diet demonstrated a 3.42 times increase in radioactivity in their tissue lipids. This late lipase response may be the result of an insufficient level of dietary lecithin (M) and a short intestinal length being ineffective, in the early larval stages, in incorporating labelled free fatty acid from dietary glycerol tri[1-¹⁴C]oleate breakdown.     

Intensive rearing system for fish larvae research II: Artemia hatching and enriching system

Live food such as Artemia is considered to be an essential part of any marine finfish hatchery. Standard methods were developed for hatching and enhancing the nutritional value of the Artemia nauplii by using different enrichment products. Although there is a variety of commercially available products in the market, further research on more specific enrichments for solving specific nutritional deficiencies in fish larvae is still required. A simple, compact and reliable experimental system was developed for these nutritional experiments. The system was built as a compact, all-in-one system with eight 50-l conical tanks in a water bath. The system reduces variation between the replicates (tanks), otherwise resulting from individual heaters and aeration. It reduces the manpower and time needed for harvesting and to re-establish the system on a daily basis by the ability to harvest, wash and refill all the tanks at the same time with the same volume of water. The system has been used for a variety of experiments, comparing commercial and experimental enrichments, bacterial monitoring and evaluation of different Artemia procedures.     

Proteolysis by juvenile sea bass (Dicentrarchus labrax) gastrointestinal enzymes as a method for the evaluation of feed proteins

Protein digestibility by gastrointestinal homogenates of Dicentrarchus labrax, was investigated in 5 feeds in relation to their amino acids composition and their ability to sustain growth of D. labrax post larval juveniles. Gastric proteolysis was found to contribute <25% of the total proteolytic capacity. Correlation was found between intestinal proteolytic capacity and the feed protein content of three pairs of amino acids. The sum of basic amino acids, arginine + lysine in the feed protein exhibited a positive correlation with susceptibility to proteolysis. The sum of the acid amino acids glycine and proline showed a negative correlation.Comparison of the intestinal proteolytic enzymatic activities in 3 growth stages of this species revealed similar profiles. Post larval and large juveniles had similar proteolytic capacities when compared on the basis of equal activity on an artificial substrate of Trypsin. Specific growth rates of post larval fish fed on these 5 feeds correlated positively with their protein digestibility as measured with large juvenile's intestinal homogenates. The results suggest that in this species, the efficiency of feeds in sustaining growth at the post larval stage can be estimated by measuring the feed protein digestibility by the proteolytic system of larger sized juveniles.     

Intensive rearing system for fish larvae research: I. Marine fish larval rearing system

Larvae nutrition and in general larvae culture is considered to be the ‘bottle neck’ for marine finfish culture. Fish larvae rearing experiments investigating nutritional factors or rearing protocols are carried out in various systems, from small beakers to very large commercial tanks, making it difficult to compare data across systems.

A continuous supply of live or dry feeds and a controlled environment, i.e. temperature, filtration, photoperiod, oxygen and pH, are essential for any experimental or commercial system. These environmental factors are best controlled automatically in order to minimize variations between tanks. However, only a few automatic systems have been developed for marine finfish hatcheries.

An experimental larval rearing system was developed to reduce variability amongst tanks (due to manual feeding and other parameters) and enhance control of environmental parameters while reducing the workload. The system includes 24 conical tanks with the option of either an up-welling or bottom draining flow through water delivery system. The inlet water passes through a gas exchange column that saturates the water with dissolved oxygen and stabilizes the pH. The system was originally designed for nutritional experiments using formulated feeds. The use of an up-welling water inlet method extends the suspension time of inert particles in the water column and also helps to suspend very small or passive swimming larvae. However, when the system is used to grow-on larvae or juvenile fish it can easily be switched to bottom draining to provide self-cleaning water dynamics for high organic loads.

A unique outlet filter was developed that eases the daily routine of replacing screens when enriched live food is used. This filter can be exchanged with a screened standpipe and outlet surface skimmer when the bottom draining flow characteristics are engaged.

The system is fully controlled by a single programmable logic controller (PLC). The PLC controls the light intensity, photoperiod, dimming time, live food and algae pumping intervals, substantially reducing labor requirements.     

Effect of varying dietary lipid and protein levels on growth and reproductive performance of female swordtails Xiphophorus helleri (Poeciliidae)

We conducted a study to determine the effect of dietary protein and lipid levels on the growth and reproductive performance of a freshwater ornamental species, the swordtail (Xiphophorus helleri). Two protein levels (20% and 30%) with four lipid levels (8%, 12%, 16%, 20%) within each protein levels were tested through formulation of practical diets labelled as 20P8L, 20P12L, 20P16L, 20P20L, 30P8L, 30P12L, 30P16L and 30P20L respectively. Results showed that dietary protein level significantly influenced final weight, weight gain and specific growth rate, while dietary lipid did not influence any of these growth parameters. More specifically, increasing dietary lipid levels from 8% to 12–16% in both 20% and 30% protein levels significantly improved swordtail growth performance. Dietary protein levels positively influenced gonadosomatic and hepatosomatic indexes. Both dietary protein and lipid significantly influenced female muscle protein content. Significantly highest fry production was obtained from diets 30P12L and 30P16L, respectively, while diet 20P8L resulted in the lowest fry production. This present study indicates the dietary protein and lipid requirements for female swordtails for optimized growth and reproductive performances to be at 30% and 12% respectively.     

The effect of dietary phosphatidylcholine and its constituent fatty acids on microdiet ingestion and fatty acid absorption rate in gilthead sea bream, Sparus auratus, larvae

This study tested the effect of the level of dietary phosphatidylcholine (PC) and its constituent medium-chain fatty acids on microdiet ingestion (μg diet larva⁻¹ h⁻¹) and the absorption rate of the free fatty acid [¹⁴C]16:0 (pmole larva⁻¹ h⁻¹) in 15, 20, 21, 25, 26, 30 and 31-day-old gilthead sea bream, Sparus auratus L., larvae. Fish were fed four microdiets (A, B, C and D): microdiet A contained no phospholipid (PL), while microdiet B included 10 g kg⁻¹ Artemia nauplii PL (3.7 g kg⁻¹ PC). Microdiets C and D contained 10 g kg⁻¹ purified saturated PC dimyristoyl (C_14:0) and polyunsaturated PC dilinoleoyl (C_{18:2[cis]−9,12}), respectively.
Larvae from one or both of the PC microdiets demonstrated significantly higher ( P < 0.05) ingestion rates (μg diet larva⁻¹ h⁻¹) than the non-PL microdiet control in 15, 21, 22, 25 and 26-day-old larvae and the Artemia PL microdiet in 15, 22 and 26-day-old larvae. However, microdiet ingestion and fatty acid absorption rate appeared to be independent of the associated medium carbon chain saturated or polyunsaturated fatty acid moiety of the PC diets. Apparent absorption, as measured by the retention of radio-labelled [¹⁴C]16:0 following 8 h of non-labelled microdiet feeding, was possibly related to feeding.     

The effect of vitamins C and E in (n-3) highly unsaturated fatty acids-enriched Artemia nauplii on growth, survival, and stress resistance of fresh water walleye Stizostedion vitreum larvae

This study aimed to evaluate the effect of enriching Artemia nauplii with vitamin C (ascorbyl-6 palmitate) or vitamin E (α-tocopherol acetate), 20% w/w, together with a mixture of concentrated eicosapentaenoic acid (EPA, 20:5 n-3) and docosahexaenoic acid (DHA, 22:6 n-3) on the growth, survival, and stress resistance of fresh water walleye Stizostedion vitreum larvae. Either cod liver oil (CLO) or EPA/DHA ethyl esters concentrate was used as lipid sources in the Artemia enrichment. Walleye larvae were fed ad libitum for 40 days. At day 40, submersion in salt water (25 g L⁻¹) was performed to evaluate larvae resistance to stress. EPA and DHA levels in walleye juveniles fed EPA/DHA-enriched Artemia increased significantly, by an average of 650% compared with fish fed non-enriched Artemia . A significant increase was found for vitamins C (71.8 ± 1.0 and 42.7 ± 1.2 μg g⁻¹ wet weight (WW)) and E (17.0 ± 3.7 and 6.5 ± 0.9 μg g⁻¹WW) concentrations in fish fed enriched and unenriched Artemia , respectively. Growth was comparable throughout treatments, whereas survival was significantly higher in fish fed CLO-enriched Artemia nauplii compared with fish fed Artemia nauplii enriched with EPA/DHA concentrate. The addition of vitamin C increased fish survival by 1.4-fold compared with fish fed Artemia enriched with only EPA/DHA concentrate. The survival of the latter was similar to control fish ( Artemia without enrichment). The supplementation of vitamin E did not affect fish survival significantly. Stress tests revealed that the resistance of walleye larvae to salinity changes increased when Artemia enrichment was supplemented with vitamin C. However, walleye larvae fed CLO-enriched Artemia had the best performances in the stress test.     

The use of squid protein hydrolysate as a protein source in microdiets for gilthead seabream Sparus aurata larvae

In the present study, the use of predigested proteins as an ingredient of microdiets offered to gilthead seabream larvae was tested. The protein source (freeze-dried squid powder) was hydrolysed with protease (trypsin and pancreatin). Different levels of raw squid protein and hydrolysate (100% protein, 50% protein/50% hydrolysate, 100% hydrolysate) were added to the microdiets to produce a dietary protein level of 65%. For comparison, cofeeding of Artemia nauplii and microdiet as well as microdiet supplemented with pancreatin were also offered to the larvae. The final average dry weights of 32-day-old larvae were 1.65 ± 0.04 mg, 1.38 ± 0.06 mg and 1.13 ± 0.1 mg, respectively, for larvae cofed 0%, 50% and 100% hydrolysate microdiets and Artemia nauplii. Survival of larvae was not affected by protein source. The survival of larvae cofed Artemia nauplii and microdiet was significantly higher than that of larvae fed exclusively on microdiet (68% and 80%, respectively). These results suggest that the use of hydrolysate (at 50% greater) as a protein source in diets for seabream larvae is not to be recommended.