Supplementation of tryptophan and lysine in Diplodus sargus larval diet: effects on growth and skeletal deformities

Amino acids are the building blocks for growth and the major energy source during fish larval stages. Deficient amino acids can be supplemented in the diets, overcoming problems such as low growth rates and skeletal deformities. In this study, three experimental diets were tested: a balance diet supplemented with lysine, a balance diet supplemented with tryptophan and a control with no supplementation. Trials were conducted with Diplodus sargus larvae from 1 to 25 days after hatching (DAH). A microencapsulated diet was introduced at 15 DAH in co-feeding with live feed and from 20 DAH larvae were fed only this diet. The effect of the supplemented diets was assessed in terms of survival, growth rate, skeletal deformities, ammonia excretion and activity of amino acid catabolism enzymes. The results showed a similar survival in all treatments. However, larvae given tryptophan supplementation had a lower weight on 25 DAH. No significant differences were found in ammonia excretion, frequency or type of deformities or enzymatic activity. Tryptophan and lysine supplementation failed to improve larval growth, survival or larval quality.     

Development of deformities at the vertebral column in Diplodus sargus (L., 1758) early larval stages

One of the bottleneck problems of Diplodus sargus farming is a high incidence of skeletal deformities at the vertebral column. In this study, the pattern of vertebral deformities were determined in three different larval batches from 2 to 30 days after hatching (DAH). During this period, 60 larvae per spawn were observed at 2, 8, 13, 15, 18, 21, 23, 25, 27 and 30 DAH and the different types and frequency of vertebral column malformations were registered. Deformities started from 8 to 13 DAH, when the percentage of deformed larvae rose from approximately 5% to 40%. At 15 DAH, skeletal malformations had frequencies up to 80% of the observed larvae. Serious malformations such as kyphosis, scoliosis and lordosis were observed at 18 DAH but seldom in percentages higher than 15%. Vertebral fusions and compressions especially affected the preurostyle region. Abnormal shape vertebrae were more frequent between vertebrae 15 and 21. Other malformations observed were hypertrophic vertebrae, more common in the trunk and caudal regions, reaching percentages higher than 50% in the former. This study has useful information concerning skeletal malformations at the vertebral column of D. sargus larvae, as it identifies the main deformities observed and the ages of highest incidence.     

Peptide molecular weight distribution of soluble protein fraction affects growth performance and quality in European sea bass (Dicentrarchus labrax) larvae

Dicentrarchus labrax were fed from 10 to 40 days posthatching with six microdiets differing in the inclusion level (60 g kg^‐1 and 120 g kg^‐1) and type of protein hydrolysate (PH; yeast, YPH; pig blood, PBPH; pig red blood cells, PRBCPH). A microdiet containing 120 g kg^‐1 fish PH (FPH) was used as a control. PH differed in their amino acid (AA) profile and molecular weight distribution and therefore the tested microdiets too. The estimated content in FAA and di‐ and tripeptides in the FPH microdiet was 2 g kg^‐1 and 44 g kg^‐1, respectively. FAA estimated levels in YPH and PBPH microdiets were 26 g kg^‐1 and 53 g kg^‐1, whereas levels of di‐ and tripeptides were 30 g kg^‐1 and 60 g kg^‐1, respectively. The estimated levels of FAA in PRBCPH microdiets were 8 g kg^‐1 and 17 g kg^‐1, whereas estimated levels of di‐ and tripeptides were 11 g kg^‐1 and 22 g kg^‐1, respectively. Results revealed that FPH may be replaced by alternative PH from yeast and pig blood products, as fish fed those diets performed, in terms of growth, survival, digestive function and incidence of skeletal deformities, as well as those fed the FPH microdiet. Using YPH, PBPH and PRBCPH, the inclusion level of PH in microdiets might be reduced to a half with respect to current practices using FPH.     

Effects of variable egg incubation temperatures on the embryonic development in Arctic charr Salvelinus alpinus

An evaluation of different thermal regimes during incubation of Arctic charr Salvelinus alpinus L. egg was conducted with regard to embryo survival and development. The study consisted of two major parts: In experiment A, a range of commonly used thermal regimes, constant and variable ranging from 2.7°C to 7°C, were tested for differences in embryo survival and developmental status of newly hatched alevins. Experiment B assessed the timing of a shift from autumn (6°C) to winter temperature (2.5°C) and its effect on embryo survival and the occurrence of spinal deformities in newly hatched alevins. In general, incubations that were initiated at temperatures below 3°C resulted in significantly higher mortality rates and spinal deformity frequencies than other treatments. Hence, Arctic charr eggs require an initial warmer period for unimpaired embryonic development. A general negative correlation was found between the duration of this warmer period (6°C) and both mortality rates and frequency of spinal deformities. The total absence of the 6°C period had the most detrimental effect, with deformity frequencies at least four times higher than all treatments with an initial warmer period. The upper incubation temperature threshold was not reached in the study. The highest temperature tested (7°C) did not result in excess mortality or increased deformity frequency. Higher incubation temperature resulted in less developed alevins at hatching, i.e. alevins were smaller with more yolk remaining. However, measurements on alevins from incubations at variable temperatures revealed different temperature effects on growth and yolk consumption during different parts of embryonic development.     

Effect of different sources and levels of dietary phospholipids on performances and fatty acid composition of pikeperch (Sander lucioperca) larvae

The aim of this study was to evaluate the effects of dietary phospholipids (PL) sources (fish gonad G‐PL and soybean lecithin S‐PL) and levels (50 and 90 g kg^?1 dry matter) on the performances and fatty acid (FA) composition of pikeperch larvae. From day 10 to day 34 posthatching (p.h.), larvae were fed with three isoproteic and isolipidic microdiets. The best results of growth and skeletal development were related to a high phospholipid level regardless of their origin and FA profile. Jaw deformities seemed associated with high dietary highly unsaturated FA (HUFA) level. The optimal level of eicosapentaenoic acid and docosahexaenoic acid (EPA + DHA) for pikeperch larvae appeared to be around 12 g kg^?1 (dry matter) associated with a PL level around 90 g kg^?1. FA composition of diets and larvae revealed a better incorporation of arachidonic acid, EPA and DHA into PL fraction especially in larvae fed with soybean PL. Moreover, 34‐day‐old pikeperch larvae may have capability of converting 18 carbon n‐3 FA into the n‐3 HUFA. Hence, for pikeperch larvae, PL from plant origin were as efficient as those from marine fish origin.     

Diet and water temperature affect growth and body deformities in juvenile tench Tinca tinca (L.) reared under controlled conditions

The experiment was designed to determine the combined effect of fish diet and water temperature on juvenile tench Tinca tinca (L.). Three diets were used: commercial dry diet for fish Aller Futura (diet F); frozen Chironomidae larvae (diet C); and Aller Futura substituted with Chironomidae at a ratio of 3:2 (dry weight; diet FC). Daily food rations and duration of the experiment were adjusted to temperatures of 20°C, 23°C and 26°C based on a correction factor q equal to 1.000, 0.779 and 0.609 respectively. The experiment lasted 92, 72 and 56 days for the respective temperatures. No mortality occurred. The highest relative growth rates were found at 26°C in diets F and FC. The lowest food conversion ratio of 1.12–1.22 (recalculated for dry weight of feed diet) was determined in fish fed diet F at 23°C and 26°C. A high value of condition index appeared to be the early warning of decreasing biological quality of fish and deformities. The lowest incidence of fish with deformities (IDef) was found in groups fed diet C (<1%), while the highest (90%) in fish fed diet F at 26°C. A lower share of dry diet in the fish food and a lower water temperature led to a lower IDef. Thus, amount of dry feed in fish diet was the major factor inducing body deformities, while water temperature only modified the effects of the dietary factor. Diet C at 23–26°C was the most cost‐effective of the tested combinations of diet and temperature.     

A balanced amino acid diet improves Diplodus sargus larval quality and reduces nitrogen excretion

Fish larvae present high amino acid requirements due to their high growth rate. Maximizing this growth rate depends on providing a balanced amino acid diet which can fulfil larval amino acid nutritional needs. In this study, two experimental microencapsulated casein diets were tested: one presenting a balanced amino acid profile and another presenting an unbalanced amino acid profile. A control diet, live feed based, was also tested. Trials were performed with larvae from 1 to 25 days after hatching (DAH). Microencapsulated diets were introduced at 8 DAH in co-feeding with live feed and at 15 DAH larvae were fed the microencapsulated diets alone. Results showed a higher survival for the control group (8.6 ± 1.3% versus 4.2 ± 0.6% and 3.2 ± 1.8%) although dry weight and growth were similar in all treatments. The proportion of deformed larvae as well as the ammonia excretion was lower in the group fed a balanced diet than in the unbalanced or control groups (38.3% deformed larvae in control, 30% in larvae fed unbalanced diet and 20% on balanced diet group). Furthermore, larvae fed the microencapsulated diets presented higher docosahexaenoic acid and arachidonic acid levels. This study demonstrates that dietary amino acid profile may play an important role in larval quality. It also shows that balanced microencapsulated diets may improve some of the performance criteria, such as skeletal deformities, compared to live feeds.     

Morphological and histological characterization of an ectopically mineralized structure in a gilthead sea bream Sparus aurata with opercular deformation

In this study, we describe an abnormal ectopically mineralized structure (EMS) that was found inside the skull of a juvenile Sparus aurata that also showed a bilateral opercular deformation. The overall phenotype and tissue composition were studied using micro‐CT scanning and histological analyses. The ectopic structure occupies a large volume of the brain cavity, partially extruding into the gill cavity. It shows a dense mineralization and an extracellular matrix‐rich phenotype, with variation in both the morphology and size of the cell lacunae, combined with an irregular fibre organization inside the matrix. This study is the first to report such an EMS in a juvenile teleost fish, where the tissue does not resemble any other connective tissue type described in bony fish so far. The tissue phenotype seems to rule out that the EMS corresponds to a tumorous cartilage. Yet, it is rather reminiscent of a highly mineralized structure found in cartilaginous fish, where it is suggested to be associated with damage repair.     

Tyrosine and phenylalanine supplementation on Diplodus sargus larvae: effect on growth and quality

Phenylalanine is the precursor of tyrosine, which is involved in the synthesis of several molecules with key roles in the regulation of metabolism and growth, stress response and pigmentation. In this study, three experimental diets were tested: an amino acid (AA) balanced diet supplemented with phenylalanine, another supplemented with phenylalanine and tyrosine and a non‐supplemented AA balanced diet. Rotifers were enriched with liposomes encapsulating free AA in order to obtain a balanced AA profile. The experimental diets resulted in similar larval survival, growth, enzyme activities of AA catabolism and nitrogen excretion in all treatments. High levels of skeletal deformities were registered and significant differences were found between the control and the phenylalanine treatment for the percentage of vertebral compressions in the trunk region of the vertebral column (30% in the control and 5% in the phenylalanine group). A significantly higher survival to a temperature stress test was found for larvae fed the diet supplemented with phenylalanine and tyrosine. The results suggest that supplementation of phenylalanine/tyrosine in fish diets may be useful in order to reduce skeletal deformities and mortalities caused by stress. The present study confirms that AA requirements may be sufficient for covering growth and survival but insufficient to cover other metabolic processes.     

Effects of two culturing techniques on the growth, survival and larval quality of Dentex dentex Linnaeus, 1758

Common dentex larvae were reared using two culturing techniques, mesocosms and intensive rearing, to determine the principal culture parameters involved in the differences observed in growth, skeletal deformations and survival between the two rearing techniques. In growth, only dry weight of larvae of 40 days post‐hatching (dph) from mesocosms was significantly higher than larvae from intensive rearing. Significant differences were observed in survival at 40 dph (6.58% in mesocosms and 1.58% in intensive rearing) and in the incidence of skeletal deformations, both for percentage of deformed larvae and for some deformation types such as those related to vertebral column and to the caudal complex. Initial larval density and initial prey density and quality are the factors suspected to affect growth and survival performance, while skeletal deformities might also be affected by tank hydrodynamics.