Hatchery and growth performance of two trout pure breeds, <i>Salvelinus alpinus</i> and <i>Salmo trutta fario</i>, and their hybrid

An allelic cross between Salmo trutta fario and Salvelinus alpinus was carried out under controlled hatchery conditions. Survival,to the eyed stage was significantly lower for the hybrid than for both purebreds. There were significant differences in survival in the eyed and yolk sac stages and from fertilization to the first feeding (p0.05). The hybrid did not display heterosis with respect to any hatchery property. During the first 45 days of nursing, there were significant differences between the purebreds and the hybrid in terms of weight gain, survival, feed conversion ratio and specific growth rate (p0.05). The hybrid was slightly heterotic (+1.69) with respect to survival however no heterosis was observed in any other property to the first feeding stage

Inhibitory effects of ammonia and urea on gill carbonic anhydrase enzyme activity of rainbow trout (Oncorhynchus mykiss)

The effects of ammonia and urea on branchial carbonic anhydrase (CA) enzyme which plays a key role in ionoregulation, osmoregulation and acid-base balance of rainbow trout (Oncorhynchus mykiss) were investigated. CA activity of the control group for ammonia and urea was determined as 1285.7 +/- 67.9 and 1261.7 +/- 60.8 EU/mg protein, respectively. The CA enzyme activities of the other groups were measured at 1, 2 and 3 h after ammonia and urea applications. The corresponding activities of ammonia were 774.9 +/- 68.8, 732.1 +/- 48.6 and 768.1 +/- 59.5 EU/mg protein, respectively and that of urea were 769.3 +/- 58.9, 638.2 +/- 147.7 and 1108.1 +/- 61.1 EU/mg protein, respectively. The differences between the initial CA activities for the controls was not significantly (P > 0.01). The CA activities were significantly (P < 0.01) inhibited both in ammonia and urea group. However, the ammonia inhibited more than urea since there was significant differences between final values of gill CA activities. (C) 2004 Elsevier B.V.. All rights reserved

Effect of nisin on biogenic amines and shelf life of vacuum packaged rainbow trout (Oncorhynchus mykiss) fillets

Nisin is a lantibiotic exhibiting antimicrobial activity against a wide range of Gram-positive bacteria, or some Gram-negative bacteria when used in combination with other preservative agents. The objective of the present work was to study the effect of a nisin treatment on biogenic amines occurrence and shelf life of refrigerated (4°C) vacuum packaged rainbow trout samples. For this purpose samples were divided in two batches: the experimental batch (CB-N), consisting of samples immersed in sterilized broth formulated with soy milk 1.4% (v/v) and whey powder 11.2 % (w/v) dissolved in deionized water with addition of nisin (500 mg L-1); the control batch (CB), consisting of samples immersed in the former broth without addition of nisin. A positive effect of nisin resulted on colour stability; in fact, the global colour index ΔE remained constant during the storage of treated rainbow trout samples, while it increased in the control. However, the behaviour of microbiota, texture, smell and biogenic amines were comparable between fillet samples treated with nisin broth and with control medium (without nisin). No inhibitory effects of nisin on biogenic amines accumulation was observed; conversely, the decline of histamine content (about 30 %), observed only in fishes of the control batch, may be correlated to the presence of histamine-degradating bacteria (Pseudomonas species). Further studies are necessary to investigate nisin action mechanism on the colour, an important physical characteristic involved in the product quality and consumer acceptability