צפוף באקווריום - על מצוקת הדגים בשבי

[מגיש החדשות]

מעט מאוד ידוע על הצרכים של דגים המוחזקים בשביה: גם בתחום המדע רווחת בעלי-החיים זהו נושא הזוכה לעניין מועט יחסית. מחקר שפורסם בספטמבר 2011 בכתב העת "Journal of Applied Animal Welfare Science", בחן את השפעת הצפיפות על דגי מידאס (Amphilophus citrinellus), דגים ממשפחת האמנוניים, הפופולריים לגידול באקווריומים ביתיים.

המחקר נפתח בהערתו של החוקר, ד"ר רונאלד ג. אולדפילד, על חוסר הידע לגבי צרכיהם של דגים. הוא מציין שבקרב אקווירומיסטים דגי המידאס ידועים כדגים תוקפניים ואלימים – עד כדי כך, שפעמים רבות ממליצים להחזיק אותם בבידוד מדגים אחרים. אך התוקפנות נתפסת לרוב כתכונת אופי טבעית של הדג, ולא כביטוי למצב מצוקה הנובע מתנאי השבי הבלתי טבעיים שבהם הם מוחזקים – כפי שחושפים ממצאי המחקר.



המחקר נערך ב- 114 דגי מידאס צעירים שנקנו בחנות חיות. בקבוצת ניסוי אחת הדגים הוחזקו באקוויריום בגודל קבוע, כששינויים בצפיפותם נערכו על-ידי הוספת דגים לקבוצה. בקבוצה השנייה מספר הדגים נשאר קבוע, והצפיפות שונתה על-ידי החזקת הדגים במיכלים בגדלים משתנים. כדי לבודד משתנים מתערבים, במחקר נוצלו דגים צעירים בלבד, בשלב שלפני התבגרותם המינית, והם נצפו מחוץ לשעות ההאכלה (כדי שרמת התוקפנות תושפע רק מהתנאים הסביבתיים, ולא מתחרות על אוכל או על נקבות). מסקנות המחקר מצביעות על כך שהתנהגויות אגרסיביות, כגון תקיפת דגים אחרים, ניפוח הזימים, או שמירה קנאית על מקומות מסתור מבודדים, נוטות להחמיר לאו דווקא כתוצאה ממגע עם מספר גבוה של דגים אחרים, אלא גם ובעיקר מנפח מים מצומצם המסופק לכל דג. במרחבים גדולים, הדגים דווקא מסוגלים להסתדר היטב גם בקבוצות גדולות: כאשר דגים הוחזקו בתנאים המדמים נהרות טבעיים הם לא נטו כלל להתנהגות תוקפנית, גם לא בקבוצות גדולות, אלא ליצירת להקות שבהן שחו במשותף. זאת בניגוד חד לאופן התנהגותם על-פי רוב בתנאי שבי, שבהם הדגים נוטים להסתגרות טריטוריאלית במרוחק זה מזה, ומתרחקים מפני הזכר הדומיננטי בקבוצה.



מסקנות המחקר מצביעות על כך, שגורלו של הרוב המוחלט של דגי מידאס בשבי הוא עגום למדי: אקווריום ביתי ממוצע קטן בערך פי עשרה מהאקווריום הקטן ביותר שבו הדגים לא גילו התנהגות תוקפנית במחקר. בראיון לניו יורק טיימס לגבי המחקר ציין ד"ר אולדפילד כי "אם אנשים מחזיקים כלבים בתנאים כאלו, הם נשלחים לכלא."

המחקר אמנם מתייחס לדגים המוחזקים כדגי נוי, ולא לניצול הנפוץ יותר של דגים, בתעשיית המזון. אם זאת, יתכן שיש במסקנותיו בכדי לספק תובנות גם לגבי תעשייה זו. דגי אמנון, שהם בין הדגים הנפוצים לגידול בבריכות דגים מלאכותיות, הם בנים לאותה משפחה שאליה משתייכים דגי המידאס, והצפיפות שבה הם מוחזקים חמורה הרבה יותר מהצפיפות המקובלת באקוויריומים: לעתים קרובותהמרחב שניתן להם גדול רק מעט יותר מנפח גופם, וכמעט שאינו מאפשר להם שום תנועה מבלי להיתקע בדג אחר. לרוע המזל, רווחתם של דגים המנוצלים בתעשיית המזון מעוררת דאגה פחותה אפילו עוד יותר מזו השמורה לקרוביהם בתעשיית דגי הנוי.

כתבה זו פורסמה לראשונה במגזין אנונימוס ומפורסמת כאן באדיבות המגזין.

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